KNEX EDUCATION Real Bridge Teachers Guide 78680

78680
REAL BRIDGE
BUILDING
Teacher’s Guide
Real Bridge Building
V3-03/11 Text:
©2011 K'NEX Limited Partnership Group Dr. Alex Wright
and its licensors. AW Education, Wrexham, LL12 7LR. U.K.
K’NEX Limited Partnership Group Acknowledgements:

P.O. Box 700 The author would like to thank Matthew
Hatfield, PA 19440-0700 Haines (M.S. Educational Technology,)
Assistant Principal, Souderton Area High
K’NEX is a registered trademark of School, Souderton PA, for his valuable
K’NEX Limited Partnership Group. contributions; these helped align the
Protected by International Copyright. activities in this Guide to US Science and
All rights reserved. Technology curricula. Additionally, Reader
#4 draws on material developed by him for
Visit our website at www.knexeducation.com use in a Technology Education curriculum
Email: abcknex@knex.com unit on Structures.
Phone: 1-888-ABC-KNEX (Toll Free)
A NOTE ABOUT SAFETY:

Safety is of primary concern in science and Caution students to keep hands and hair
technology classrooms. It is recommended away from all moving parts. Never put fingers
that you develop a set of rules that governs in moving Gears or other moving parts.
the safe, proper use of K’NEX in your
classroom.
www.knexeducation.com
1-888-ABC-KNEX
Table of Contents
TABLE OF CONTENTS
Introduction 2-3 6. Spanning Gaps: Beams or Arches? 103-105

7. Investigating Cantilevers 106-113
How to Use the K’NEX Real Bridge 4 8. Investigating Suspension Bridges 114-117
Building Curriculum Materials
SECTION II:
Readers 5-35
CASE STUDY OF A BRIDGE DESIGN
1. What Is The Function Of A Bridge? 5-6
Teacher’s Notes 118-121
2. Bridges and Forces 1: 7-8
The Basics
Table of Contents
3. Bridges and Forces 2: 9-13
SECTION III:
Beams and Columns
A BRIDGE CONSTRUCTION PROJECT:
4. Stress, Strain, Stiffness and 14-17
AN EXERSICE IN TEAMWORK
Young’s Modulus
PLANNING AND IMPLEMENTATION
5. Making Strong Structures 18-23
6. Different Types of Bridges 24-35
SECTION I: SKILL BUILDERS SECTION IV:

Teacher’s Notes 36-80 WORKING AS DESIGN ENGINEERS:
An Overview 36 THE K’NEX PEDESTRIAN BRIDGE
1. Building a Bridge Can’t Be All 37-39 PROJECT
That Difficult, Can It? Teacher’s Notes 125-127
2. Investigating 2-D Shapes: 40-44 Design Engineering Guidelines 128-132
Rectangles and Squares For Students (For Photocopying)
3. Investigating 2-D Shapes: Triangles 45-49 Suppliers Price List and Order Form 133
4. Strengthening 2-D Shapes 50-54 (For Photocopying)
5. Making 3-D Frame Structures: 55-61
Cubes
6. Spanning Gaps: Beams or Arches? 62-67 SECTION V:
7. Investigating Cantilevers 68-74 AN INTERDISCIPLINARY ACTIVITY
8. Investigating Suspension Bridges 75-80 FOR REAL BRIDGE BUILDING
Student Inquiry Worksheets

(For Photocopying) GLOSSARY 139-141
1. Building a Bridge Can’t Be All 81-82
That Difficult, Can It?
2. Investigating 2-D Shapes: 83-86 ADDITIONAL READING/
Rectangles and Squares RESOURCE LIST FOR STUDENTS 142
3. Investigating 2-D Shapes: Triangles 87-90
4. Strengthening 2-D Shapes 91-95
5. Making 3-D Frame Structures: 96-102 USEFUL WEB SITES 143
Cubes

1
Introduction
Overview As students use this K’NEX set they will

This Teacher’s Guide has been developed have the opportunity to acquire skills through
to support you as your students use the a hands-on, inquiry-based approach to
K’NEX Education Real Bridge Building Set to information and concepts. Working
investigate famous bridges from around the cooperatively, students are encouraged
to interact with each other as they build,
world. Using the K’NEX materials provided
investigate, problem solve, brainstorm,
and maintaining a comprehensive journal will
discuss, and evaluate scientific and
enable your students to develop their knowledge technological design principles in action.
and understanding of structures through the
context of seven different bridge designs with
varied histories. The materials included in this
Guide offer you a wide choice of activities
TEACHER’S GUIDE
Intended as a resource for the teacher, the
Introduction
and extensive background information to

Guide contains the following sections:
enhance your understanding of the scientific,
technological, and mathematical concepts • How to Use the K’NEX Real Bridge
related to the bridges your students will be Building Curriculum Materials: This
studying. The resource information is provided schematic offers a visual overview of the five
for your benefit as you present the materials and types of activities included in the Guide and
to assist you in answering student questions that suggests a roadmap that you may wish to
may arise during discussions in the classroom. follow as you introduce them into your
The versatility of the K’NEX Real Bridge Building classroom. The schematic demonstrates
Set allows it to be used across a wide range how the activities can be used sequentially
of grade levels and subject areas, including or individually in the manner that best fits
college-level civil engineering classes. As a your own teaching program for this area of
the curriculum.
result, you may find that some materials
included in this Guide are less suitable than
• Readers: These provide background
others for the middle school learner. You are information on the factors engineers take
the best judge of what is appropriate to meet into consideration as they design bridges.
the needs of the students you serve. Topics covered by the six Readers include
the engineering principles that have been
applied to allow bridges to support the
K’NEX REAL BRIDGE BUILDING loads they must carry, the materials used
This K’NEX construction set is designed to assist in their construction, and an overview of the
students in their study of the history, function, characteristic features of the main types
structural design, geometry and strength of of bridges. Fully illustrated with diagrams
bridges. An investigation of bridges will help and photographs, the Readers are designed
students learn and experiment with the forces for use by both teachers and students; those
affecting all structures. They will also investigate that include concepts more appropriate
concepts related to the physical properties of for upper grade levels have been identified.
materials and their application in the placement, It is anticipated that the Readers will be
design, and construction of bridges. Bridge photocopied and made available for
building requires complex engineering solutions assigned reading or as resources for
that are based on sound mathematical and research projects.
scientific concepts.
2
Introduction
• Teacher’s Notes: These are provided for • Additional Reading/Resource list for
Section I: Skill Building; Section II: Case Students: A short reading list to take your
Study of a Bridge Design; Section III: A students further and for them to use in
Bridge Construction Project; Section IV: research projects.
Working as Design Engineers; and Section V:
An Interdisciplinary Activity for Real Bridge • Useful Web Sites: This list is intended
Building. Student objectives are identified for use by the teacher, but it could be
and scripts, with background notes, are reproduced and made available to students
provided to assist you, the teacher, as you for research. The sites were active at the
present each activity associated with the time of going to press.
bridge models. Most of the activities can
be completed in 30-45 minutes after the • CD-ROM of Building Instructions: This
bridges have been constructed. Bridge contains the Building Instructions files for
construction can be a time consuming task each of the K’NEX Real Bridges and acts
Introduction
but the rewards, in terms of the cooperative as a supplement to the colored Building
learning and problem solving aspects of the Instruction booklets that accompany the set.
project, as well as the pride derived from the The files may be printed and distributed to
successful completion of one of the massive students to facilitate group construction of
bridges, are deemed well worth the effort the model bridges.
and the time. There are also extension
activities that can be used to explore in
greater depth the concepts associated with STUDENT JOURNALS
the various activities. We recommend that
It is expected that students will have journals
you review your curriculum and state
available to record information, thoughts, and
standards to identify which of the activities
investigations. They should be encouraged
provided in the Guide best meet the needs
to enter their initial thoughts as they begin each
of your students.
inquiry. These initial thoughts may be amended,
based on their on-going inquiry and analysis,
• Student Inquiry Sheets: These are provided
until the student is able to draw informed
for Section I: Skill Builders and Section IV:
conclusions. The students’ journal entries
Working as Design Engineers. In the Skill
will assist them as they make connections
Builders section, each Inquiry Sheet provides
between the behavior of their models during
an introduction to the activity, a materials list,
experiments and the bridges the models
step-by-step guidelines for undertaking the
represent. In addition, their written responses
investigation, and a series of questions to
will encourage the use of newly learned
help students focus their observations.
vocabulary associated with structures, and
Students are expected to record their
will provide an opportunity for them to write
observations in their journals, using
across the curriculum. The journals also
annotated drawings and notes (see below).
offer a place for students to practice drawing
The Inquiry Sheets should be photocopied
annotated diagrams of bridges and their
so that, at a minimum, every group of 2-3
structural components. Finally, the journals
students has a copy.
serve as an assessment vehicle for the
bridges unit.
• Glossary: A comprehensive list of key terms
and definitions associated with structures, in
general, and bridges, in particular.

3
4
How To Use The K'NEX
Real Bridge Building Curriculum Materials
Bridge Construction: An Exercise in

III Teamwork, Planning and Implementation IV
II Working as Design
A project team of 4 – 6 students must plan • Analyze the building plans
Case Study of a and organize their activities to complete the of a K’NEX Real Bridge model. Engineers: The K'NEX
Bridge Design construction of a large-scale K’NEX Real Pedestrian Bridge Project
• Assign tasks and roles to
Bridge model within a limited time scale.
team members.
A collaborative investigation for They adopt the roles of construction engineers
A whole class activity in which
who must turn 2-D designs into 3-D reality. • Work collaboratively to:
4 - 6 students. Students investigate teams take on the roles of design
To complete the task students must: • Formulate a construction plan.
and evaluate the design of a named engineering companies.
• Implement the construction plan.
bridge. The K’NEX Real Bridge
• Evaluate their performance.
Building set provides examples of Students develop a range of key
7 famous bridge designs, some of skills through working on a design
which needed innovative engineering project in which they:
solutions to solve the problems caused
by the location and the need to safely • Design a bridge to meet a
span longer and longer gaps. Provides client’s specifications and
opportunities for cross-curricular I company profit parameters.
links to:
• Draw plans.
• Information Technology – using the Skill Builder Activities • Cost the project to include
Internet for searches within set materials and construction time.
Progressive investigations to develop students’
parameters; working as part of a
knowledge and understanding of the following: • Plan its construction, in
team on a multimedia presentation.
competition with other
• Geography - the impact of bridges class-based companies.
on local economies, and on human Key Concepts Key Skills
and ecological environments. • The effect of forces on 2-D and • 3-D spatial awareness.
3-D shapes and materials. • Team building skills.
• History - tracing the technological • Use of triangulation to strengthen • Problem solving skills.
developments in bridge design and frame structures. • Modeling, testing, evaluating
construction materials. • Strength of structures and materials. and modifying their ideas as
• Civics – understanding the planning • Stress, strain, stiffness and part of the design process. V
process and funding issues involved Young’s modulus. • Interpreting 2-D drawings to make Interdisciplinary Activity
in large-scale projects. • Using technical and scientific vocabulary 3-D models and to make their
in context. own 2-D drawings and plans from
Using the Real Bridge Building
• How key concepts are applied in the 3-D models.
set as a foundation, this activity
design and construction of structures
allows science and mathematics
– Real Bridges.
teachers or technology and
mathematics teachers to work
together to enhance students’
understanding of the math and
science concepts related to
suspension bridges.
Starting Point
Reader 1
What is the function of a bridge?

INTRODUCTION It was functional because it was designed to
open so that ships could pass through and it
A bridge is a structure used to cross some
form of barrier, making it easier to get
from one place to another. From earliest times
was also relatively inexpensive to build, yet
many thought the design ugly, with one critic
barriers such as rivers made it difficult for asserting that it resembled ‘an upside down
travelers and traders to carry goods by the rat trap.’1 By the time the funds had been
shortest, quickest and safest route. People raised to build the bridge, the design had
on foot, of course, could wade across a evolved into an aesthetically graceful
Reader 1
shallow stream or use stepping-stones, but suspension bridge, linking the city of San
these solutions were less suitable for heavily Francisco to the Marin Peninsula, while its
loaded, wheeled vehicles attempting to cross construction, during the 1930s, led to the
deep, fast flowing rivers. Any historical study rapid growth in prosperity of both the city
of bridges, therefore, demonstrates the ways and the formerly rural region to the north.
in which human ingenuity and resourcefulness
have been applied to their design and
construction in order to improve the movement THE BRIDGE BUILDER’S
of people and goods from place to place.
DILEMMA: HOW TO MAKE
Today, engineers design and build bridges LONGER AND STRONGER BRIDGES
that range in size from superstructures
The earliest bridges were probably fallen
crossing wide estuaries to small pedestrian
trees or stone slabs placed across small
bridges spanning busy roads, from bridges
streams or gaps – what today would be called
connecting countries and cultures to those
a simple beam bridge. (Note: the word ‘beam’
linking different parts of a building, and from
is derived from an Old English2 word for ‘tree’.)
structures joining chains of islands to elevated
This is the simplest form of bridge, constructed
sections of highways linking one part of a
from a horizontal beam supported at each
transportation system to another. Whatever
end by piers. A beam may be defined as a
they carry – motor vehicles, trains, pedestrians,
horizontal structure that is subject to bending
animals, pipelines, or open channels of water –
and deflection. A beam supported at only
every proposed bridge presents a different set
one end, such as is used in a diving board or
of challenges to the structural engineers who
bookshelf, is called a cantilever beam. The
design and construct them.
piers may be columns or pillars or some form
of natural foundation.
DESIGN FACTORS
A bridge’s final design will be determined
not only by the nature of the barrier to be
crossed, but also by the economic, social,
environmental and aesthetic requirements of
the communities that it will serve. The original
design for the Golden Gate Bridge in California,
for example, was a cantilever bridge, with
a modified center section lifted by cables.

5
Reader 1
Fig. 3: Strengthening a beam by making it thicker
As the need arose to carry heavier loads across

wider and wider barriers, the science and
Reader 1
technology associated with bridge building

developed. People soon discovered that simply
making the beam longer did not bring the
desired solution to the problem of crossing
a wider barrier – long beams tend to bend, Shear
or sag, in the middle.
Fig. 4: The bridge itself is too heavy
The problem with the bridge shown in Fig. 4

is that it has been thickened so much that its
own weight has become greater than the
internal strength of the material from which it is
made. Although it looks strong, it is unable to
support its own weight and it will fail (collapse
or fracture) or, at best, it will be very weak.
Fig. 1: Long beam Fig. 2: Short beam
bending remains rigid The weight of all the materials used to make
a bridge is called the dead load and this must
be taken into consideration when calculating
Short beams are stronger than long beams the load bearing capacity of the bridge. The
of the same thickness, so why not make the weight of all the objects carried on a bridge is
beam thicker? called the live load. The dead load and live
load together provide an estimate of the
Increasing their thickness or depth can working load.
certainly strengthen beams. This action,
however, creates yet another problem. When the total load capacity is taken into
By thickening and extending its length, the
consideration, the longest single span for a
beam becomes much heavier, more difficult to
beam bridge is approximately 80 - 100 meters.
construct, and more costly to transport into
position. A point will also be reached when the A beam bridge, therefore, could not be used
beam is so long and heavy that the material in every location and in order to cross wider
from which it is made can no longer support barriers, new bridge designs were needed.
its own weight, causing it to bend even before
it has to support a load. 1. http://www.pbs.org/wgbh/amex/goldengate/index.html
2. Old English: Words that have been in use before
AD 1150.
6
Reader 2
Bridges and Forces 1: The Basics

DESIGNING A STABLE STRUCTURE Look at Fig. 1, which shows a truck crossing
a simply supported beam bridge
A successful bridge or structure is one that
does not collapse, but how can engineers
be confident that their design will not have the Beam
same disastrous results as the Tay Rail Bridge
in Scotland, which collapsed during a storm
while a train was crossing it, or the Tacoma A
Load
Reader 2
Narrows Bridge in the U.S.A. that literally shook
itself apart? The answer lies in making sure
that the strength of the bridge, including the B
Columns/Piers
materials from which it is made, is able to
support all the forces that may act on it. Fig. 1: Action and reaction in the bridge
From Newton’s Third Law of Motion you know

As the truck crosses it, the bridge does not
that for every action there is an equal and
bend. This is because the resistance from
opposite reaction. In other words, if you push
internal forces in the beam balances the
against a wall (action) it pushes back against
weight of the load acting on it – the reaction
you (reaction). Nothing moves. The harder you
of the beam.
push, the harder the wall pushes back. Still
nothing moves. At all times the forces cancel
Now consider what is happening to the
each other out – they are equal in strength and
bridge piers:
opposite in direction. Because no movement
takes place, the action and reaction forces can • At A, the weight of the beam and load push
be said to be balanced or in equilibrium. vertically down on the piers, which in turn
push back against them with an equal force –
If, however, you can push the wall down, the the reaction of the piers.
forces are no longer balanced – the action is • At B, the total weight of the bridge and
now greater than the reaction and movement load pushes against the foundations of the
takes place in the direction of the greater pier, which in turn push back with an equal
force. The result is the wall moves or breaks. and opposite forcethe reaction of the
Applying this concept to a bridge, if the action foundations.
(load) is greater than the reaction (the strength
of the bridge), movement will take place in the Failure will occur, however, if at any place
direction of the larger force – the bridge will on the structure, the vertical forces pushing
collapse. (Newton’s Second Law of Motion.) down become greater than the ability of the
structures to push up. Imagine, for example,
Estimating all the load forces that may act on what might happen if the ground below one
a bridge is not an exact science. Structural of the pillars could not take the load.
engineers know how to design structures that
will successfully support loads and they know The challenge for the engineer is to design a
the strength of the materials from which it will bridge so that all the forces acting on it are
be made, but it is very difficult to know the equal and opposite in direction. When this has
size of natural forces that may act against been achieved, the forces are in equilibrium and
their structure. These they can only estimate. the bridge is structurally stable.

7
Reader 2
WHAT OTHER FORCES ACT ON • What other load factors must they take into
consideration? For example, environmental
LARGE STRUCTURES SUCH AS loading caused by, among other things,
BRIDGES? high winds, currents, or snow build-up on
the structure.
Additional considerations that engineers must
factor into their design calculations include
• What factor of safety should they establish
the shock load, which results from a sudden,
so that it takes into account a worst-case
high impact, such as a train or heavy truck
scenario? For example, a traffic accident that
crossing a bridge, and environmental load,
causes all lanes on a bridge to be filled with
resulting from the effects of strong winds,
stationary traffic, combined with heavy snow
rain, ice and snow build-up, river and tidal
and high winds. To account for such an
currents and earthquakes. Some bridges,
Reader 2
event an engineer might increase the values

such as cable-stayed and suspension bridges,
for loads acting on parts of the structure by
are not designed for train traffic because of
5 times, as a factor of safety.
their susceptibility to shock load, while the
Tacoma Narrows Bridge in Washington State
• How the materials they might use behave
collapsed because engineers did not fully take
when subjected to large forces or stresses.
into account the environmental effect on the
A material becomes stressed when a force
structure of wind blowing at a constant speed
is applied to it and, as a result, may change
for a long period of time.
in length and so become strained. (See
Reader 4 for a more detailed discussion of
these terms.)
QUESTIONS AN ENGINEER
WILL NEED TO ASK
People expect a bridge to be safe at all times,
no matter how long it is or what the weather
and other environmental conditions are like.
Since these are issues confronting all structural
engineers, what types of technical information
do they require before they begin their
calculations? The following are some questions
they will need to ask:
• What is the maximum distance that the

bridge must span?
• What type of rock will underlie the bridge

supports? For example, will the piers or
towers be constructed on soft sedimentary
rocks or on resistant igneous or
metamorphic ones?
• How large a working load is the bridge

expected to carry?
8
Reader 3
Bridges and Forces 2:

Beams and Columns
FORCES ACTING ON BEAMS • Torsion: a force that acts to twist a material.
Example: wringing out a wet cloth.
I f you stand on a plank of wood it may bend,
but if you jump up and down on it you may
find it breaks. This is because jumping up and
• Shear: forces that act in opposite directions
against a material. Example: the cutting
down produces larger forces than just standing action of a pair of scissors.
Reader 3
still. Simply standing on the beam creates a
static load while jumping up and down creates
dynamic loading.
Fig. 2: Compression Fig. 3: Tension

(squeezing) (stretching)
Fig. 1: Long beam bending
As the name implies, static loads do not move.

An example of a static load is the weight of a
roof on a building. Dynamic loads, by comparison, Fig. 4: Torsion Fig. 5: Shear
move and change and produce much greater (twisting) (sliding)
forces in structures. The effect of a person
jumping up and down may increase the load
Stress can cause a decrease in length
on the beam by as much as 6 times. Although
(compressive stress) or an increase in length
bridges and other structures may be designed
(tensile stress). The result of compressive
to support mainly static loads, the effects of
stress is compression and the result of tensile
dynamic loads such as wind and moving traffic
stress is tension. While compression and
must also be taken into account.
tension are the most common forces affecting
bridges, torsion and shear can also occur.
External forces acting on parts of a structure,
or structural members, are called stresses.
When an external force (load) presses down on
They include:
a beam, compression and tension forces are
• Compression: a force that acts to squeeze produced – the top edge of the beam is put
a material. Example: stepping on a soda can. under compression, while the bottom edge is
• Tension: a force that acts to stretch a put under tension. If the load is large enough,
material. Example: pulling a rubber band. the beam will bend. Bending is the result of
excessive compression and tension in a
horizontal beam or column.

9
Reader 3
Subjecting a beam, or any material, to an one side. Draw a horizontal line equidistant from
external force causes the internal forces that the top and lower edges.
hold the molecules of the material together
to react. They resist being pushed apart or Neutral
squeezed together. As the external forces Axis
increase, there is a similar increase in the
opposing forces from the molecules being
pushed apart or squeezed together.
Think about what happens when you stretch

a rubber band. As you stretch it, you can feel
a force working in the opposite direction
Neutral
Reader 3
(the reaction, or resistance, of the material). Axis

If you remove your stretching force the rubber
band will go back to its original size. On the
other hand, if you continue to stretch the rubber
band it will continue to get longer until a point is
reached when it will stretch no further. Continue
to increase the stretching force and the band Fig. 6: Using foam rubber to demonstrate compression
snaps. Its breaking point has been reached. and tension lines in a beam
The same process is at work in a beam –
Place the foam rubber strip between two
a point will be reached when the external forces
blocks of wood or books. Either add a load or
become greater than the ability of the material’s
push down at the mid-point. As the beam bends
internal forces to resist and it will break (fail).
the effects of compression and tension can be
seen. The lines on the upper edge will move
The ability of a material to resist being
closer together while those on the lower edge
changed in shape is called stiffness. Stiffness
will move further apart.
can be used as a measure of the strength of
a material. For example, compare the amount
If a single section of the beam is examined in
of force that is needed to bend a piece of
more detail it is possible to see that compression
steel, which has a high stiffness value, with
is greatest at the top edge and tension is greatest
the amount needed to bend a piece of rubber,
at the lower edge. At the neutral axis, the beam is
which has a low stiffness value. Much more
neither in compression nor in tension and its
force is needed to bend the steel than the
length remains the same.
rubber and using this measure we would infer
that steel is a stronger and more suitable
material for building a bridge than is rubber. Compression is greatest at
top edge as demonstrated
by a decrease in the width
NOTE: Students in upper grade levels may want of the segment.
to explore this concept further in Reader 4.
Neutral Axis
You can see compression and tension in
action in a simply supported beam. A simply
Tension is greatest at lower
supported beam is one that is supported at edge as demonstrated by
both ends, as shown in Fig. 6 below. Use a an increase in the width of
the segment.
rectangular strip of solid foam rubber with
equidistant parallel vertical lines drawn along
Fig. 7: The effect of bending stresses in a simply
supported beam
10
Reader 3
Concentrated load
Compressive
forces
Tensile forces
Strain
Fig. 10: A long thin beam showing excessive bending

Fig. 8
Reader 3
In a cantilever beam the opposite situation Excessive bending or deflection can occur in
occurs, with tension on the upper edge and long, lightly loaded beams. For example, in long
compression on the lower edge. spans using wooden beams.
A useful website to visit to explore these

concepts further is:
http://www.pbs.org/wgbh/buildingbig/bridge/
basics.html (b) From shear forces
Short heavily loaded

HOW MIGHT BEAMS FAIL beams may be subject to
If the compressive and tensile stresses are too shear failure near the points
great for the material from which the beam is where they are supported.
made, it will fail.
(a) From bending

Load
Fig. 11: Failure due to shear forces
WHAT THICKNESS OF BEAM WILL

BE NEEDED TO SPAN A GAP
Hairline cracks caused WITHOUT BENDING?
by tension in the beam.
Structural engineers use an equation called the
span-to-depth ratio to help them estimate the
Fig. 9: Thick beam failure
thickness, or depth, of a beam they might use
to span a gap.
The strength of the material in tension and
compression has been exceeded. For example, Length of beam (span)
although concrete is strong under compression, Span-to-Depth Ratio =
Depth of beam
it is weak under tension.

11
Reader 3
How does the ratio help calculate the Suggested Reading For
dimensions of a beam needed to span
a barrier? Upper Grade Levels
For a material with a span-to-depth ratio of
25:1, for example, an unsupported beam used FORCES ACTING ON COLUMNS,
to span 25m would have to be 1m in depth. PIERS AND WALLS
To cover a span of 50m, unsupported, the
Columns, pillars, bridge piers and walls are
thickness (depth) of the beam would have
examples of vertical supports designed to take
to be increased to 2m.
vertical loading.
Although it is a simple equation, there is a
Vertical loading means that the compression
Reader 3
limiting ratio for each type of construction

stresses produced by the load act axially along
material. This is because the properties of
the length of a column. Both compression and
materials (including the ways in which they
tension are the result of axial forces acting on
respond to compression and tension) are
a structural member.
different. The span-to-depth ratio for steel,
for example, should not exceed 25:1, while
the ratio for wood cannot exceed 12:1. This
means that steel has a higher span-to-depth
Compression
ratio than wood so that, for a given depth of
bridge beam, a steel bridge can span a longer Tension
gap than can a wooden one. There are also
limits on the ratio for different designs of beam
bridges, so that the ratio used for a simply
supported beam will differ from the one used
for a cantilever beam.
This web site highlights Pre-Stressed Girder

Bridges:
http://www.cpci.ca/?sc=bs&pn=
prestressedgirderbridges
Fig. 12: Axial forces acting vertically and horizontally
on columns
How a column behaves depends on the strength

and stiffness of the material it is made from and
its slenderness ratio. The slenderness ratio is
the ratio of the height of the column to its width.
12
Reader 3
Load B: Long, slender columns

These tend to buckle before the deformation
becomes permanent. If the force is released
before permanent buckling occurs, the column
Load will return to its original shape, as could happen
with long bamboo canes.
C: Intermediate length column

Kneeling will occur when some areas give
Fig. 13: Height and the slenderness ratio way before buckling occurs, as may occur in
a tubular steel chair leg.
Reader 3
Increasing the height of the column increases
the slenderness ratio but the load bearing The slenderness ratio for pre-stressed concrete
capability of the column decreases. For is about 10:1 which means a 10m tall column
example, a short piece of dowelling will not of pre-stressed concrete would have to be
bend under a large load but a long piece 1m in diameter and for every 1m increase in
bends easily. Generally a short, wide column height, the diameter of the column must
can support a greater load than a long, increase by 10cm.
slender one.
How do structural engineers use this ratio to
Columns can fail under compression by compare materials?
crushing (A), buckling (B), or kneeling (C).
The slenderness ratio value for steel is 40:1,
while that for pre-stressed concrete is 10:1.
This means that a 10cm diameter column of
A B C steel can support the same compressive forces
(load) as a 40cm diameter column of concrete.
Columns will also bend first in the weakest
direction, so a square column with its
symmetrical dimensions will be stronger than a
rectangular one with asymmetrical dimensions.
Considerations such as these must always
be factored into the calculations made by
engineers as they develop their design for a
structure.
Fig. 14: Column size and the effects of compression
A: Short, wide columns

The main factor here is the strength limit of the
material. Brittle materials such as concrete
may crumble and break, while softer materials
such as those used to make a soda can, will
crush without first buckling or bending.

13
Reader 4
Stress, Strain, Stiffness

and Young’s Modulus
Suggested Reading For produce extremely small, measurable, changes
in the structure.
Upper Grade Levels Only
Structural engineers must also design bridges
that are not only able to resist deformation by
PROPERTIES OF MATERIALS USED IN
Reader 4
large stresses but which are also flexible and

MAKING BRIDGES AND OTHER able to change. Changes of temperature, for
example, will cause bridge materials to expand
LARGE STRUCTURES and contract, while bridges built in areas subject
It is important for structural engineers to know

and understand how the materials they plan
to use behave when subjected to any type of
to seismic activity should be able to flex in
response to earth movements.
force. From previous Readers you will know

that when forces are applied to a material, it STRESS
will become stressed. As a result of stress, the
It is much easier to pull and break a thin thread
material may change in length. When the length
than a thick rope, or to walk across deep snow
of a material has been changed it has become
using snowshoes than without them. A person
strained. Compressive stress produces a
wearing snowshoes will spread the load over
shortening in length while tensile stress
a much larger area, reducing the stress on the
causes an increase in length. The result will be
snow and as a result he or she will not sink into
compression or tension in the material. Some
the snow very far. Without snowshoes the
materials are strong under compression –
stress on the snow is high and the person sinks
wood, reinforced concrete, steel, stone, bricks
much deeper. This demonstrates the concept of
and some plastics; other materials are only
point load versus distributed load.
strong under tension – rope, string, paper, steel
cables and wood (when cut along the grain).
You might assume that small loads will have

little effect on the massive steel girders that
make up a bridge, or the bricks in the wall of
a house. In fact, all structures and materials
are deformed to some extent when loaded.
Some changes are so small they cannot be
seen unless measured using very accurate
equipment; others are more obvious. When
you squeeze a sponge, stretch a rubber band
or walk across a plank, for example, the effects
can be clearly seen. The effects of the weight
of people on a steel girder in a building or on These examples also highlight two key points
the legs of the chair, however, are not usually about stress. The amount of stress to which a
visible to the naked eye and yet they do material is subjected, whether it be thin thread,
14
Reader 4
snow, a plank of wood, a brick, or a steel Stress values for different materials vary widely.
girder, depends on (i) the size of the force (F) Some examples are given in Fig. 2. Note: the
and (ii) the area (A) over which it is applied. higher the value, the greater the resistance of
the material to external forces.
Force (Newtons)
Stress =
Area (m2)
Fig. 2: Examples of stress
values for common materials
• A force applied over a small area produces
high stress. Material Stress value MN/m2
Steel 400 - 1000
Reader 4
• A force applied over a large area produces
Cast iron 150
low stress.
Wood 100
Aluminum 70
Consider, for example, the foundations of a
bridge column:
STRAIN
Strain is a measure of the change in length
caused by stress. Values for strain are obtained
by putting a material under tension and
Column measuring the change in length produced by
a load. The change in length is then compared
to the original length.
Foundations Change in length

Strain =
Original length
Fig. 1: The small area immediately below the column For example: Ropes and steel cables stretch
base will be subject to high stress levels whereas the when used to lift heavy loads. When lifting the
much larger area of the foundations will be subjected same load, a 5m rope may increase in length
to low stress. by 0.04m, whereas a steel cable, with the same
diameter and lifting the same load, may increase
If the concrete column in Fig. 1 has a in length by only 0.0006m.
cross-sectional area of 0.1m2 and is being The strain values:
compressed by a load of 100,000N the stress
on the column can be calculated as follows:
Rope
Force (Newtons) Strain = Change in length = 0.04m = 0.0080
Stress =
Area (m2) Original length 5m or 0.80%
= 100,000N = 1MN/m2
0.1m2 Steel cable
Strain = Change in length = 0.0006m = 0.00012
(NOTE: 1MN = 1Meganewton = 1,000,000N; Original length 5m
1MN/m2 = 146 psi) or 0.012%

15
Reader 4
Strain values are often expressed as WHAT DO STRESS-STRAIN

percentages. The much lower value for the
CURVES TELL US?
steel cable tells us that steel is a stronger
material than rope because it showed a greater
The steepness of the slope is the key.
resistance to its length being changed.
This graph (Fig. 3) has a steep slope, which
indicates that a very large stress, or load, is
When designing structures it is very important
needed to produce a small change in length
to know how stress affects the length of a
(strain). Steep slopes are typical of strong
material. A graph of stress against strain
and stiff materials such as metals.
provides additional information.
Fig. 3: Graph of stress against strain

From the origin (O) to point E, the material
obeys Hooke’s Law. In other words, the
Reader 4
extension of the material is directly

proportional to the load. (The strain is
proportional to the stress).
E B
Y: 4MN
Yield Point
Stress
3MN
2MN
Stress
0 1MN
Strain
Strain
O-E: In the straight part of the graph, the change
in length is proportional to the applied load Fig. 4: The gray areas show the increase in length
(Hooke's Law). In this part of the graph, materials (strain) caused by the values of the tensile stress in the
usually return to their original shape once the load boxes. As the tensile stress increases, so the increase
is removed. Materials that behave in this way are in length increases so that the dotted line joining all
said to be elastic. the bars is a straight line. In other words, the increase
is proportional to the stress.
E: Elastic Limit
Beyond this point the material cannot return to its Many materials are elastic, provided they are
original length and will be permanently deformed. not stressed beyond point E (the elastic limit).
This means that when the stress is removed, the
Y: Yield Point material will return to its original length – just like
The material has been permanently strained. a rubber band.
B: Breaking Point
If the material is stressed beyond the elastic
If the stress increases beyond this point the
material breaks. limit, a point is reached at Y (yield point) when
a marked increase in length can occur, and even
when the stress is removed, the material will not
return to its original length. The material has
been permanently strained, as shown in Fig, 5
on Page 17.
16
Reader 4
YOUNG’S MODULUS
By comparing the slopes of the straight-line
parts of the stress-strain graphs, it is possible
to compare the relative stiffness of different
Fig. 5: This material has been stretched beyond its materials. The measure of the stiffness of a
elastic limit (dotted line) and is permanently strained. given material is known as Young’s modulus
or the modulus of elasticity.
If the stress is continued, the material will
eventually break. Point B on the graph shown in The symbol used to represent Young’s modulus
Fig. 3 represents the material’s breaking stress is E and can be simply calculated as:
point.
Reader 4
Stress
Different materials produce different Young’s Modulus =
Strain
stress-strain graphs.
Example:
Steel A sample of mild steel produced a strain of
0.002 when subjected to a stress of 420MN/m2.
Aluminum
Young’s
420MN/m2 = 210,000 MN/m2
Modulus = Stress =
Stress Concrete (E) Strain 0.002
Wood
When designing structures, engineers use
Young’s modulus to help choose the right
material for a particular structure.
(See Fig. 7 below.)
Strain
Fig. 6: Stress–strain graphs Fig. 7: Young's modulus values for some

common materials used in structures.
The steeper the slope of the stress-strain Material E MN/m2

graph, the stronger and stiffer the material. Steel 190 - 210,000
Some materials, such as bricks and concrete, Wrought iron 190,000
have a steep slope but break before they reach Cast iron 83 - 170,000
their elastic limit. They are very difficult to Titanium 110,000
stretch and they snap easily. Such materials are Aluminum Alloy 70 -79,000
said to be brittle. On the other hand, a ductile Granite 40 - 70,000
material is one that can be stretched without Concrete 17 - 31,000
sudden failure, for example metals such as Softwoods 11 - 14,000
steel.

17
Reader 5
Making Strong Structures
O ne of the many factors that structural

engineers must consider when undertaking
a project, is cost. Thickening a cable or beam,
• Can paper be used to make structures?
What are its strengths and weaknesses?
(increasing its cross sectional area,) may allow

that part of the structure to support a much
greater load before it reaches its breaking
point, but doing this may also increase both
the weight and cost of the structure. Engineers,
Reader 5
therefore, must find ways of making structures

lighter while using less material, or using Fig. 1a
materials in different ways to make them strong.
Their goal is to use the minimum amount of Paper Forces
material possible to keep down costs and still
meet strict safety standards.
Some materials are strong under compression

– wood, reinforced concrete, steel, and some
plastics, for example; others are strong under Fig. 1b
tension - rope, string, paper, and wood – when
cut along the grain. By combining materials it
is often possible to get the benefits of both. This test demonstrates how paper is strong
Many bridges, for example, are constructed under tension but weak under compression.
from reinforced concrete. Concrete, a cheap
material, is strong under compression but • Is it possible to change the structural
weak under tension. Steel is strong under properties of materials?
both conditions, but it is expensive to produce.
Long steel bars are not rigid, but may bend
under their own weight. Reinforced concrete
has steel bars running along its length and so
is strong under both tension and compression.
This makes it a good choice for many types
of structures because it is relatively cheap to
produce, is rigid, and is strong under tension
and compression.
Experimenting with the properties of reinforced

concrete is not usually possible in the classroom,
but testing the properties of paper, cardboard,
wood, drinking straws or even spaghetti, under Fig. 2: Limp paper
different conditions, demonstrates how materials
can be modified to make them suitable for use
When held between your hands, a sheet of
in structures.
copy paper flops down – it is not very rigid.
When folded, however, it has different properties.
18
Reader 5
Paper tubes, used in the right way, however,

can make quite strong structures. Similarly,
hollow steel tubes are often used in structures
to provide strength, while keeping the amount
of steel used, and hence costs, to a minimum.
The ability of a tube or column to support a

load depends on a number of things including
the shape of its cross-sectional area and its
length. For example, a short, wide tube will be
Fig. 3: Making paper rigid
able to support larger loads than a long, thin
one; a square column will support a larger load
The sheet of paper is now rigid and can than a narrow rectangular one of the same
Reader 5
support some surprisingly heavy loads. Try test- cross-sectional area.
ing its load bearing capacity.
By changing its shape, we can make what at
first appears an inappropriate material into one
that can be used to make strong structures.
Balsa wood and spaghetti do not come to mind

as strong bridge building materials, but used in
the right way, quite strong bridge structures,
able to support many times their own weight,
can be made from these materials.
Fig. 4a Fig. 4b Fig. 4c SHAPES USED IN STRUCTURES

4 shapes are commonly used in structures:
Paper columns squares, rectangles, triangles and arches.
Rolling a sheet of 8.5” x 11” (or A4) paper

to make a tube produces a structure that is
surprisingly strong. Try to compress (squeeze)
it along its length (axially). You may want to
discover what type of load the tube of paper
can carry before buckling (failing). Paper
composites are actually used to make parts of
passenger aircraft because they are strong but
very light.
• What types of load can the tube of paper

carry before buckling (failing)?
Tubes, even paper ones, are strong under

compression and tension, but not strong in
resisting bending forces (see Fig. 4c).
Fig. 5: Shapes commonly used in structures

19
Reader 5
• What happens to these shapes when STRENGTHENING A SQUARE -

forces are applied to them?
TRIANGULATION
RECTANGLES Materials such as wood, concrete and steel
are strong under compression. In the activities
When a rectangle or square is squeezed from
described below K’NEX Rods behave as if they
corner to corner, their shapes are changed.
are strong materials. By adding a diagonal
They now become parallelograms and therefore,
brace to a square so that the forces act
on their own they are unstable shapes to use in
axially (along its length), the square can be
structures.
strengthened and reinforced. It is now a
rigid, stable structure.
A brace is a strengthening or reinforcing

Reader 5
component of a structure.
Fig. 6
Diagonal
Brace
Fig. 10: Strengthening triangles

Fig. 7
Fig. 6 & 7: Pushing at a corner - using K’NEX models.
By creating triangles (triangulation), square can

Key be strengthened and reinforced so that they do
not change shape when forces are applied to
their corners. Braces that resist compression
are called struts and those that resist tension
are called ties.
Fig. 8
Fig. 9
Fig. 8 & 9: Loading the top - using K’NEX models Fig. 11: Tension acting on the tie
The force or load causes both the top and the

sides to bend, with the sides bending outwards.
20
Reader 5
Fig. 13: Forces applied to the sides of triangles
Reader 5
If, however, a load or force is applied at one of
the angles, the triangle does not bend because
the two sides are squeezed and the base is
stretched. The forces acting on the triangle are
Fig. 12: Using string to create a distributed around the whole structure, not just
stable rectangular structure
on one side.
A single, rigid brace on a square can be replaced

by two non-ridgid cables or ropes. Tightly tie
string to the corners of your square as shown
above. If you use your hands to place a force on
the shape as shown by the dark arrows on the
drawing one of the strings will resist the force
thus strengthening the square. If you use your
hands to place a force on the shape (in direction
of big arrows) the other string will resist the force
thus strengthening the square. In a real-world
application of this principle, steel cables are
used in place of the string in your model. They
can strengthen both square and rectangular
components of structures.
TRIANGLES
If a load or force is applied to one of the sides of
a triangle, the side may bend inwards. The side
is the weakest point in a triangular structure.
Fig. 14: Force applied at the angle of a triangle
Used in the right way, triangles are the most

stable and rigid shapes that can be incorporated
into the design of a structure.

21
Reader 5
When designing structures, engineers try

to eliminate any bending forces acting on
structural members as this can produce
weaknesses; instead they attempt to exploit
the strength of materials when under either
compression or tension.
Fig. 15b
ARCHES
Arches have been used in structures for
thousands of years. Many arched bridges and Fig. 15a and Fig. 15b: Forces acting on an arch
aqueducts built by the Romans are still in use
Reader 5
today – a testimony to their strength.

If, however, the sides are buttressed by
external supports, these will push back with
a reactive force and stop the sideways thrust.
With the addition of these external supports –
called abutments – all the forces will be acting
to compress/squeeze the whole arch together.
This results in a very strong structure.
Fig. 16: Strengthening an arch
When a load is applied to the top of an arch,

Arches, however, do have their limitations. If the
the top moves down, while the sides tend to
arch span is too large in relation to its height,
move outwards. In other words, compressive
the structure is weakened because much larger
forces applied to the top of the arch produce
reaction forces from the abutments are needed
thrust at the base.
to balance the sideways thrust of the arch.
Engineers are concerned with the ratio of the arch

span and the height (or rise) of the arch – the
span-to-rise ratio. In general, the span-to-rise
ratio for steel arches is in the region of 30:1, which
means for every 1m rise there can be a 30m
increase in the span.
Fig. 15a
22
Reader 5
Modern arch bridges, such as the Sydney

Harbour Bridge, are made from steel frames
because steel allows the construction of longer
arch bridges than those made from stone.
The largest single span arches today are
approximately 250 meters wide.
Reader 5

23
Reader 6
Different types of bridges
If you have ever looked at bridges while

traveling in your local area, or on trips to more
distant places, you may have identified many
different designs. The Chesapeake Bay Bridge,
for example, looks very different from the
Golden Gate Bridge, and while the Golden
Gate has some similarities to the Dames Point
Bridge, it bears no resemblance to the Astoria
Reader 6
Bridge. Or does it? In fact most bridges have

developed from just two basic designs – the
beam and the arch.
Fig. 1: Forces in a beam bridge

BEAM BRIDGES
The pillars
or piers
supporting
the weight
of the bridge
are under
compression.
• Construction and materials

The beam bridge supports its own weight
and its load on upright, or vertical, piers. It
is typically used to span narrow distances Long beams are much weaker than short
over small streams or rivers, or over beams of the same thickness.
highways. While wood and stone were
commonly used for this type of bridge
construction in the past, modern beam
bridges are usually constructed from steel
and reinforced concrete.
• Forces acting on the bridge

The forces acting on a beam bridge tend to
compress the top but stretch (place under
tension) the bottom of the beam. The piers
supporting the weight of the bridge are
under compression.
Fig. 2: Long beams are weaker than short ones
24
Reader 6
Increasing the thickness of the beam can make • Construction and materials
this type of bridge stronger and more rigid. A truss bridge is a type of beam bridge in
This, however, not only increases the cost, which the beam is constructed from a lattice
but can also make the bridge much heavier. of straight sections, usually made from steel,
A point will eventually be reached when the that are joined together to form a series of
bridge cannot support its own weight and it triangles (triangulation). Constructing a beam
will fail. (See Fig.4 in Reader 1.) There are, using triangles offers three advantages:
therefore, only a limited number of sites (i) the beam can be thicker
where a simply supported beam bridge can (ii) the weight of the beam is not significantly
be used successfully. increased
(iii) the technique creates a strong, rigid
structure.
Reader 6
TRUSS BRIDGES
Early truss bridges included just a few triangles
and were made from wood (see Fig. 3 & Fig. 4).
Fig. 3: King Post Fig. 4: Queen Post

truss design truss design
As better materials, such as wrought iron

and steel, became available, trusses became
more complex, incorporating larger and larger
numbers of triangles in their designs. In some
cases the beam is “bow shaped,” thicker in
the middle to provide greater strength where a
simple beam would bend the most, and thinner
at either end, where it bends least.

25
Reader 6
Fig. 5a: Problem: The bridge bends and is weak

Reader 6
Fig. 5b: Solution 1: Push up from below
While the addition of trusses can increase the

strength of a beam, truss bridges also have Fig. 5c: Solution 2: Pull up from above
limits on their maximum practical length. The
longest steel truss girder bridges are around
500m long.
Available Options
1. Using multiple spans and
LONGER BRIDGES supporting piers
A long, simply supported beam bridge will bend
in the middle when loaded. Engineers have
CONTINUOUS SPAN BRIDGES
attempted to overcome this problem in two
ways. They have designed bridges so that the
weak point in the structure (where it bends) is
either pushed up from below by a pier or pulled
up from above by cables or some other method.
These two techniques have resulted in a variety
of bridge designs, capable of spanning longer
distances, but still based on the beam.
A different approach to spanning wider barriers,
one that has been in use for more than 2000
years, is to use an arch structure. What follows
is a brief overview of the design options
available to engineers taking on a new bridge
building project. Photo Courtesy of the Chesapeake Bay Bridge-Tunnel
26
Reader 6
Instead of using a long, single span that is Each pier is firmly embedded in bedrock and
likely to bend in the middle, engineers can build the deck extends out on either side of the
bridges using many small beams that are joined supporting pier. Imagine yourself standing with
together. The Chesapeake Bay Bridge-Tunnel both arms held out horizontally – your arms are
in the U.S.A. is constructed in this way and is acting as cantilevers. The weight of a cantilever
known as a continuous span bridge. The bridge system is supported by its piers, which
bridge, (and tunnel), extends across the shallow in turn must be supported by the bridge
Chesapeake Bay, for about 26 kilometers, but foundations and the bedrock.
the longest single span is only 30 meters.
In the cantilever system, the weight of the deck
(and/or the anchors/counterweights) on the
landward side of the pier balances the weight
Reader 6
of the deck extending over the gap. A good
analogy to help you think about this is a
seesaw – if you make one arm of a seesaw
longer you must then increase the length of
the other arm by the same amount to keep it
balanced, or you must add weight to the
shorter arm.
Keeping the forces balanced allows the beam

to extend far over the gap with a minimal
amount of additional support. The beam can
be balanced either by:
1. Extending each span outwards, away from

the pier to make a T-shaped structure – like a
giant seesaw.
2. Using Cantilevers 2. Adding counterweights, or anchors, at the
CANTILEVERS BRIDGES ends of the cantilevers, where they meet the
A cantilever bridge is another variation of a shore – like a parking lot barrier. The anchors
beam bridge. In this type of bridge there are serve as weights at one end of the system,
usually two beams, extending out from so the part of the beam extending beyond
opposite sides of a barrier. Each cantilever the pier, over the gap, can be made longer.
beam is supported by one pier only. Often
an additional beam is suspended on the two
beams to form an even longer span.
Additional Beam
Cantilever Cantilever
Pier Pier
Fig. 6

27
Reader 6
Cantilevers in Action Even more strength could be added by pulling

the beam upwards at the same time. The supports
To see cantilevers in action you will need
above the beam are subject to tension and help
5 books of an equal size (or wood blocks).
balance the compression forces acting on the
Stand two books vertically – these represent
lower supporting struts.
the supporting piers. Lay a book, horizontally,
on each of the piers – these represent the
This is the basis of the design for the Forth
cantilevers. Each pier and cantilever should
Rail Bridge. (See diagrams/photographs below.)
look like a letter T. Now connect the two
cantilevers by balancing another book across
the gap or by moving the two cantilevers
together so that they meet. It may be necessary
to counterbalance the horizontal beams when
Reader 6
a load is applied to one end.
Fig. 9
Fig. 7
Adding struts below the cantilever will provide

additional support. The struts are joined to the
bridge’s piers and are subject to compression.
If, however, the struts are long and thin they
might bend and buckle and so additional
support could be needed.
Fig. 8
28
Reader 6
Note the additional bracing The massive tubes take the

and struts to keep the forces weight of the bridge and are under
from buckling the main compression. They are also held
structures. up by the narrow top members.
Reader 6
Fig. 10
The Forth Rail Bridge, crossing the wide estuary of the Firth of Forth near Edinburgh, Scotland
is one of the world’s largest cantilever bridges. It was constructed of steel in 1890 and has a
length of approximately 2500 meters. Its central span between the two cantilevers, however, is
only 100 meters wide.
In this example the rail decking is supported from below by struts and from above by ties.
Additional support is provided by a latticework of triangles above and below.
Like the Forth Rail Bridge, many cantilever

structures have a triangular shape. These
include roofs for train and bus stations,
sports stadiums, some carports and even
bookshelves.
Jacques-Cartier Bridge, Montreal, Canada:

a cantilever bridge that incorporates a
supporting steel truss structure.

29
Reader 6
3. Using cables to pull up

from above
A. SUSPENSION BRIDGES
The use of suspension bridges quite possibly
dates back to pre-history – vines in forested
areas may have been used to construct
footbridges across narrow valleys. Today, Anchorages
suspension bridges form some of the longest
bridges in the world. Fig. 11
Reader 6
Trusses
• Constructions and Materials
Modern suspension bridges use steel cables
strung between two towers, which support
the weight of the bridge. The cables pass
Anchorage
over the tops of the towers and their ends
are anchored in the bedrock. The decking
is suspended from vertical cables, called
suspenders (or hangers), which hang down
from the main cables. The road decking itself
may be gently arched, with a truss structure
to provide additional strength and rigidity.
Cables
Suspenders
Towers
30
Reader 6
• Forces acting on the bridge B. CABLE-STAYED BRIDGES

The design of suspension bridges, like any Cable-stayed bridges include design elements
other type of bridge, must ensure that the from both cantilever and suspension bridges:
forces acting on the structure are balanced the road decking of the bridge is the cantilever
and are working together in harmony. structure, suspended by cables from a tower.
With a suspension bridge, the cables and Each tower supports a balanced portion of the
suspenders are under tension as they are deck by way of its cables. While the design
always being stretched, while the towers are idea is not new, this type of bridge became
under compression because the cables and increasingly popular from the mid-20th Century
the weight of the road decking push down onwards, largely due to developments in
on them. construction materials (pre-stressed concrete).
Reader 6
They are also relatively inexpensive to build
because, unlike a tower-to-tower suspension
bridge, they do not require anchorages. As a
result, a cable-stayed design is often selected
for locations where, in the past, a medium sized
(under 1000 meters) suspension bridge would
have been built. It is also worth noting that
advances in technology have resulted in the
Fig. 12: Forces acting on a suspension bridge construction of cable-stayed bridges with
lengths over 2500 meters.
The Humber Bridge: Total length - 2220 meters
The very longest bridges built today are

suspension bridges, capable of spanning
lengths of 4000 meters. The Akashi Bridge,
linking the Japanese islands of Shikoku
and Honshu, for example, has a length of
3,911 meters.

31
Reader 6
Reader 6
• Construction and Materials

Cables, attached to a tall tower, are used
to support the bridge road decking. The
cables run directly from the tower to the
deck. Towers are typically constructed from
concrete or steel, while the cables exhibit
great variety in their design. (See Fig. 14.)
• Forces acting on the bridge

All the cables are under tension and the
tower, which is under compression, supports
the total weight of the bridge and everything
on it.
Fig. 14: Cable designs
NOTE: We encourage you to visit

www.brantacan.co.uk/cable_stayed.htm
where you will find a helpful summary comparing
the features of cable-stayed bridges with those
Fig 13: Forces acting on a cable-stayed bridge of suspension bridges.
32
Reader 6
4. Using arches • Construction and Materials

The arch draws its strength from the ability of
ARCH BRIDGES blocks of stone, (or concrete, bricks, wood,
The arch was used in structures built by ancient or steel), to withstand very large forces of
Egyptian and Chinese engineers, as well as in compression. These forces hold the stones
the buildings, bridges and aqueducts together between the abutments of the bridge.
constructed by the Romans.
In the arch bridge, the forces of compression
are spread (dissipated) from one block to
the next, along the curve of the arch towards
its ends (abutments) and into the ground.
The ground, in turn, pushes back on the
Reader 6
ends of the arch, creating a resistance that
is transferred from one block to the next until
the keystone, or central block, is reached.
When the arch bridge is made from masonry
blocks, their shape is critical. Blocks (called
voussoirs) must be wedge-shaped, as it is
this shape that makes it possible for the arch
to hold itself up. The wedge-shape ensures
that each block is caught between neighboring
blocks, preventing it from falling. If the blocks
were rectangular, they could slip out of place,
causing the bridge to collapse.
Fig. 15: Forces acting on an arch
All parts of an arch bridge are under compression

– from the weight of the bridge deck pushing
out along the curve of the arch and from the
resistance of the ground pushing back (reactive
force) on the abutments. Tension, by comparison,
is a minor force in an arch, even on its underside,
although the steeper the curve of the arch, the
more tension is likely to be present.

33
Reader 6
The use of abutments is a critical design

feature of the arch bridge. Note how both ends
of the Victoria Falls Bridge, which spans the
Zambezi River and links Zambia and Zimbabwe,
abut against the rock face of the ravine. These
abutments prevent the ends of the bridge from
thrusting outward.
Many older arched stone bridges were

constructed from multiple arches. For example,
Reader 6
the original London Bridge, the Ponte Veccio

in Florence, Italy and the Old Bridge in
Beziers, France.
Fig. 16: Old London Bridge
With time, bridge materials improved and arch bridges were made with cast iron, steel and,
more recently, with concrete. The longest single span arch bridges are around 500 meters in length.
34
Reader 6
Moving Bridges
BASCULE BRIDGES A castle drawbridge
The word BASCULE is French and means
‘seesaw.’ A bascule bridge is often used to
cross rivers and canals and can be opened to
allow the passage of ships. Its central span is
divided into two sections called leaves. The
ends of the leaves must be counterbalanced A drawbridge is a variation of a bascule bridge.
to reduce the effort needed to raise them. Both types of bridge use the principle of the
Each leaf is in fact a rotating cantilever. lever to operate.
Reader 6
The movable sections rotate upward to open
the bridge and are operated by a system of
counterweights, gears and motors. The
counterweights themselves are typically made
from concrete and are normally located below
the roadway. A motor operates the opening
mechanism; it turns the gears that move the
counterweights down, while the leaves pivot
up and open a passage for shipping.
A bascule bridge opening for shipping
Bridge Disasters
Engineers must be concerned about safety
at all times but occasionally bridges fail.
When bridges collapse lives are at stake
and the economy of a region may be affected.
Tower Bridge, crossing the River Thames in It is therefore crucial for structural engineers
London is a bascule bridge. Each bascule is to investigate and learn from past mistakes
approximately 33 meters (100 feet) long and in order to avoid similar disasters happening
each has a 422 ton counterweight attached at again.
one end.
Investigate further by visiting the following
web sites:
http://eduspace.free.fr/bridging_europe
/disasters.htm
http://www.engr.utexas.edu/wep/COOL/
AcidRiver/allaboutbridges_Disasters.htm
Tower Bridge, London, England.

35
Skill Builder
Teacher’s Notes
An Overview for the Teacher
It is often assumed that all students know how

to use construction kits simply because many of
those used in schools have their origins as children’s
By following the K’NEX Building Instructions when
making the K’NEX Real Bridge models, students also
learn how to interpret 2-D drawings to make 3-D
toys. Differences in opportunities and interests, models and to make their own 2-D drawings and
however, resulting from gender, race/ ethnicity, plans from 3-D models.
socio-economic background, and ability will mean
that such knowledge is far from universal in the Skill Builder activities are presented as a collection
classroom. With this in mind, teachers may want to of practical investigations. Working through these
provide opportunities for all students to become activities enable students to develop their knowledge
familiar with the different components that make up a and understanding of basic concepts relating to
SECTION I
kit, with the techniques used to fit them together, and structures, in general, and to bridges, in particular.
with ways to identify them when trying to interpret In addition, students are encouraged to use different
building instructions. It is also important for students resources, including the Internet, to investigate and
to recognize both the advantages and limitations of evaluate the design and construction of bridges, and
construction kits when used to model, test, evaluate to develop team building and problem solving skills.
and modify their ideas as part of the design process.
The activities outlined in the Skill Builder section can
When designing and making their own models, be used sequentially or individually in the manner that
students need to develop their sense of spatial best fits your own teaching program for this area of
awareness. The capability to visualize structures the curriculum.
and/or working mechanisms is a skill that has to be
learned and this can be best achieved by working SUMMARY
in a 3-D environment. In addition, designing and Objectives
creating, whether using a construction kit or not, Students will learn to:
requires students to have a knowledge and • Become familiar with K’NEX building
understanding of the properties of the materials techniques and components.
with which they will be working, how they join or fit • Explore how K’NEX components join together
together and how they move in three dimensions. to make simple 2-D and 3-D shapes.
The K’NEX construction system is easy to use, • Construct 3-D models from 2-D drawings.
but it is recommended that students be given • Develop a knowledge and understanding
some free building time to explore and investigate of stable and unstable shapes and simple
the components before starting structured activities. structures.
The activities outlined in the Skill Builder section
• Use technical and scientific vocabulary in context.
are designed to familiarize students with K’NEX
components and to develop a K’NEX technical
Key Skills
vocabulary that everyone can understand and use
Students will learn to:
when describing their designs and their models.
• Understand and apply key concepts relating
Concurrently, students will have the opportunity to
to structures.
learn the technical and scientific vocabulary needed
to discuss and describe the concepts they observe • Develop 3-D spatial awareness.
and use in different bridge designs and structural • Work as part of a team.
design problems. Throughout the Skill Builder
section, opportunities are presented to reinforce • Problem solve.
students’ prior learning and to develop further their • Use K’NEX resources effectively.
knowledge and understanding of how structures
are designed and made.
36
Skill Builder 1
Teacher’s Notes
Building a Bridge Can’t Be All

That Difficult, Can It?
INTRODUCTION Teams of 2-3 students are presented with 3
challenges:
T his is a ‘free building’ activity in which no
prior knowledge of bridge construction is
assumed. Students are provided with a limited
• Design and build the longest bridge, without
a load, that will not fail.
set of resources and are given a limited ‘design • Design and build the longest bridge capable
and create’ task to carry out. Their performance of carrying a small load.
in this activity establishes a baseline measure of • Design and build the longest bridge that
SECTION I
their knowledge and understanding of structural can support a small load without sagging
engineering concepts and it is against this that or bending.
individual progress can be monitored as they
work through this part of the curriculum.
MATERIALS
OBJECTIVES Each group of students will need
• 15 K’NEX Rods (any length)
• To establish the baseline knowledge and
understanding of construction technology of • 15 K’NEX Connectors (any type)
the students through a limited investigation. • K’NEX Real Bridge Building Instructions
Booklet (Page 2)
• By discussion, to help students identify some
• 50g and 100g weights/slotted masses
of the key problems that must be solved by
structural engineers when designing and • Rulers
building structures.
• To introduce and use in context the technical

and scientific vocabulary associated with
VOCABULARY
physical engineering. beam, load, dead load, live load, span, bending,
sagging, rigid, fail, failure, strength, design
The activity can also be used as an introduction specifications, structure
to the design process. A limited task to be
completed within a set time, with limited
resources, is a reflection of real life engineering CHALLENGE I
design. The students will learn not only through • Using only the specified materials, students
trial and error, but also through reflection and design and make the longest bridge. It does
discussion about how well their design worked. not have to support a load, but it must not fail.
They will also discover that designing and
making structures involves considering many • The bridge does not have to be a free-
factors in order to successfully confront the standing structure, but can simply span the
challenges of the project. gap between two desks or two chairs.

37
Skill Builder 1
Teacher’s Notes
• Students can use a maximum of 15 K’NEX • What ideas were rejected/accepted and
Rods (of any length) and 15 Connectors the reasons for their decisions?
(of any type) in their bridge construction. • How their bridge performed against their
expectations/the design specification.
• Maximum thinking and building time allowed:
20 minutes. • What changes they made to the bridge
structure during construction to make it
meet the design specification.
CHALLENGES II AND III Given that the students only have a small
• Allow a maximum of 15 minutes for each number of components to work with, the
challenge. most likely bridge constructed will be a simple
II. Using only the specified materials, beam bridge.
students design and make the longest
SECTION I
bridge that can span a gap and support In attempting to make a long bridge they should
a 100g load at its mid-point? find that the beam will soon start to sag under
its own weight (dead load) and a bridge more
III. Using only the specified materials, than 7 or 8 of the longer K’NEX rods in length
students design and make the longest may be so weak as to break under its own
bridge that can support a 50g load weight.
without sagging or bending? Students should also discover:
• In order to carry a load (live load) a bridge
Question: must be structurally strong enough to
Of the three bridges each group has made, support both the dead load and the live load.
which is the strongest?
• Long span beam bridges have a lower load
bearing ability when compared to short
span beam bridges made from the same
PROCESS pieces and to the same design.
WHOLE CLASS
K’NEX structures, along with many other
• Allow a few minutes for students to select
structures, are likely to fail where structural
their construction materials from the K’NEX
components are joined together. It is at the
Real Bridge Building set.
joints or connections that stress forces focus.
Any weakness here will result in structural
• Before starting their ‘design and create’
failure. Careful observation of the connections
challenge, students may be introduced to the
in their K’NEX model will show how they may
K’NEX building tips shown on Page 2 of the
be forced apart by bending forces.
Real Bridge Building Instructions Booklets.
WORKING IN GROUPS 2-3 ASSESSMENT

• After the construction and testing,
• Students should be encouraged to spend a
students should provide a short report of
few minutes discussing how they might
approximately 100 words on the strengths
tackle the challenge before starting to build.
and weaknesses of each of their 3 bridges.
• They should be asked to record their ideas
and observations. They may want to address
some of the following areas:
38
Skill Builder 1
Teacher’s Notes
WHOLE CLASS Reference Material for Upper Grade Levels

• Discuss the merits and issues raised by the • Reader # 4: Stress, Strain, Stiffness and
success and failure of each group’s design. Young’s Modulus.
• What did the students learn about bridge

structure and function? How and where did EXTENSION ACTIVITIES
their structures fail? To extend the activity you may find it useful
for students to investigate some famous bridge
• Why is it important for the beam to remain disasters such as the Tacoma Narrows Bridge
rigid when subjected to a load? in 1940; the Quebec Bridge 1907, 1916 and
the Tay Railway Bridge 1897. Film footage and
• What changes might they make to strengthen photographs of the Tacoma Narrows Bridge
their design so that the beam will remain rigid failure is available on a number of web sites.
SECTION I
over a longer distance, even when a load
passes over it? http://www.ketchum.org/bridgecollapse.html
Provides references to a number of bridge
• How do structural engineers solve the collapses, video footage of the Tacoma
problem of maintaining a stiff bridge span Narrows Bridge and graphics of the Tay
structure over long distances? Refer the Railway Bridge disaster.
students to the photographs in the K’NEX
Real Bridge Building instruction booklets or
visit www.brantacan.co.uk.
• Discuss how most people take it for granted

that a bridge will not sag when they drive or
walk across it. Would the students feel safe
using a bridge that sagged? Automobiles
and trucks would also find it difficult to use
such a bridge. Additionally, it is not only
the live and dead loads that must be taken
into consideration but also environmental
loads such as wind, snow, ice and currents
of water.
• You may also wish to introduce the importance

of the choice of materials in bridge design.
Explain how the ability of engineers to design
and construct longer and longer bridges only
advanced with the discovery and use of new
technologies and materials. Wood and stone
were superseded by cast iron, wrought iron
and then steel. Today many bridges are
constructed using reinforced concrete and/or a
combination of different materials. Understanding
the physical properties of materials and how
they behave when subjected to different types
of forces is essential knowledge for any
successful structural engineer.

39
Skill Builder 2
Teacher’s Notes
Investigating 2-D Shapes

Rectangles and Squares
INTRODUCTION THE INVESTIGATION
• To make as many different sized rectangles
In this activity students investigate the
effects of forces acting on rectangular frame
structures. The activity also offers a context
and squares with the available components
and to investigate the effects on them of
within which to introduce technical vocabulary external forces.
relating to structures and the forces acting
SECTION I
on them. • Each team selects blue, red and gray Rods

and an assortment of Connectors from which
they will construct 3 different sized squares
and 1 rectangle. The rectangle should be
OBJECTIVES made using blue and either red or gray Rods.
Students will:
• Investigate the effects of forces on rectangular
and square shapes.
SAFETY NOTE: Please refer to the beginning
of the Guide for information on the safe use
• Learn, understand and use technical
of rubber bands in the classroom. Protective
vocabulary correctly.
glasses/goggles should be worn during the
activities described below. This is sound safety
practice for the science/technology classroom
MATERIALS or lab.
• K’NEX Real Bridge Building set(s)
• A piece of solid foam rubber approximately PROCESS
30 x 6 x 6cms (12 x 2 x 2”) WORKING IN GROUPS 2-3
• Marker • Explain how a rectangle is one example of
• Rubber bands – at least 12.5cms (5”) long a frame structure, made by joining together
a number of parts or members.
• Access to the Internet
• Discuss how the strength of a structure
lies in its ability to resist being distorted or
VOCABULARY deformed when external forces are applied
stable, unstable, strength of structures, strength to it.
of materials, frame, structure, member, strut, tie,
compression, tension, shear, distort, stress, • Use simple drawings on the board and/or
compressive stress, tensile stress, equilibrium, use the Student Inquiry Worksheets
lateral applied forces. to introduce the investigations and the
vocabulary to be used.
40
Skill Builder 2
Teacher’s Notes
• Students will use their models to carry out To help visualize what is happening, it is useful
a simple investigation of the strength of to place a rubber band, under a small amount
rectangular frame structures. of tension, in line with the applied forces.
Additional stretching or relaxation of the band
• They should be encouraged to record their shows lines of compression or tension in
observations through drawings, using the structure.
directional arrows to indicate
compression Suggestion: Use 4 yellow Rods and 4 blue
and tension , Connectors. Hook the ends of the rubber band
and write notes, using the correct technical over the prongs of the opposite Connectors.
vocabulary. Use a rubber band that is at least 3/4 the length
of the diagonal of the quadrilateral. If you use
the arrangement suggested above you will need
EXPECTED OUTCOMES a rubber band that is approximately 12.5cms
(5”) long.
SECTION I
Applying external forces to squares and
rectangles will affect their shape, especially of
those with longer sides. Students should find
that as external forces are applied, the joints on WORKING IN GROUPS 2-3
the K’NEX Connectors begin to open. At this • Ask: Does the addition of more squares or
point no further pressure should be added rectangles make the structure stronger?
to the structure.
• Each group should make a chain of squares
or rectangles and investigate the effect of
external forces on this structure. (Additional
K’NEX Rods and Connectors will be needed).
For example:
Shearing forces
Students will discover that a chain of repeating

shapes does not increase the stability of the
structure. It will still distort when subject to shear
and that even small downward forces at its
Compression forces center will cause it to bend. They should also
note that the joints on the bottom are forced
open indicating that this part of the structure is
under tension.
WHOLE CLASS
• Review student results.
• Rectangles and squares are easily distorted
by external forces and are therefore
Tension forces unstable structures.

41
Skill Builder 2
Teacher’s Notes
• Joints are often weak points in many IMPORTANT SAFETY NOTE: If the structure
structures and are points where structural is squeezed too hard the joints may snap open
failures may occur. ejecting one or more connecting Rods from
the structure. While this effect demonstrates
• K’NEX structures, along with many other a dramatic failure of the structure, students
structures, are likely to fail where structural should be instructed not to exert too much
components are joined together. It is at the force because of the potential hazard from
joints or connections that stress forces focus. the ejected rods. Wearing protective
Any weakness here will result in structural eyewear is advised.
failure. Careful observation of the connections
in their K’NEX model will show how they may
be forced apart by bending forces.
EXTENSION ACTIVITY
• You may wish to introduce the concept of
SECTION I
• Explain that rectangles and larger polygons

are unstable because external forces strong and weak structures at this point.
acting on them easily distort their shapes. The strength of a structure is measured by
This can be explained in terms of balanced the size of the external forces needed to
and unbalanced forces as determined by make it break or fail. For example: rectangles
Newton’s First Law of Motion. This states and squares are weak or unstable structures
that an object will remain at rest unless it is because their shapes can be distorted easily
acted on by a force that makes it move in when forces are applied.
the direction of the applied force.
Reference Material for Upper Grade Levels
• When a student pushes a structural member • Reader #4: Stress, Strain, Stiffness and
in a K’NEX square/rectangle, that member Young’s Modulus
will move from its rest position, resulting in
the distortion of the square. The shape,
however, will only be distorted if the applied THE INVESTIGATION
external force is larger than the structure’s Students will carry out a simple investigation
ability to push back against it. The movement to find out what happens when compression
of the structure will be in the direction of the and tension forces are applied to a structural
larger force. member – in this case a plastic K’NEX Rod.
The forces are applied by gently squeezing a
• How do structures/inanimate things K’NEX rectangle by hand. The students should
push back? try with different sized rectangles/squares.
Demonstrate by allowing students to stretch
rubber bands. As the students pull the ends
apart they feel a force working in the opposite
direction.
PROCESS
What happens to their K’NEX models when WORKING IN GROUPS OF 2-3
they remove the external force? It returns to • Ask: From the students’ experiences
its original shape. If, however, the size of the in Skill Builder 1 can they predict what
applied force is the same as the structure’s might happen?
resisting forces, the forces acting in the
structure remain balanced, their net sum • Students push the sides of their K’NEX
equals zero. The structure is stable and will rectangle inwards (lateral applied forces)
not change shape. and observe the effect on the shape.
42
Skill Builder 2
Teacher’s Notes
When external forces are applied at right angles

to the long axis of structural members, they
bend in a similar way to a beam bridge. The top
and bottom members may also be affected.
An earlier activity referred to the need for

structural engineers to have an understanding
of the physical properties of materials. This
knowledge enables them to predict how those
materials may behave when used in structures.
This may also be a relevant time to introduce

Forces are applied at right angles to the long the ideas relating to strength of materials.
axis of the side members. The strength of a material is a measure of
how much force must be applied to it to make
SECTION I
• Next, ask students to place the K’NEX model it break or fail.
vertically on the desktop and push down on
one of its edges. You may wish to explain that the way in which
In other words, the external force is applied a structural member behaves is dependent on
along the axis (axially) of a K’NEX rod. how the external forces are applied. Ask the
students to consider the following situations:
1. Force is applied at right angles to the long

axis but the internal forces operating in the
beam are not strong enough to resist.
Expected outcome: The structural member
bends. Bending causes compression on one
side of a structural member and tension on
the other.
• Demonstrate to the class compression and

tension in a beam using a piece of foam
rubber marked along one side with parallel
lines equidistant from each other, as
shown below.
WHOLE CLASS Neutral

• Review student results. Axis
• Ask: Did the shapes behave as you

expected? Describe and explain your
observations.
• Students should observe that long structural Neutral

members bend more easily than shorter ones. Axis

43
Skill Builder 2
Teacher’s Notes
As the beam bends, the lines on the top WHOLE CLASS

surface of the beam move closer together Discuss whether rectangles and squares are
showing that the top of the beam is being good shapes to use in structures.
squeezed, or is under compression, while
those on the lower surface are stretched Ask: How can weak rectangular frame
further apart, showing that the bottom is structures be made into strong structures?
under tension. At the neutral axis of the
beam it is neither in compression nor tension.
2. Force is applied axially. EXTENSION OF CONCEPTS

Expected outcome: Applying force to the
edge of a K’NEX square does not make it
(OPTIONAL)
move because two things are happening: In a follow-up to this lesson you may wish to
SECTION I
2.1. A student’s downward pushing force is expand on the concepts of stress, strain and
balanced by an upward force (reaction) from elasticity in materials.
the table. The harder the student pushes
down, the more the desk pushes back. The For example:
K’NEX model does not move; it remains Stress as a measure of how much the atoms/
at rest. molecules in materials resist being pushed
together or pulled apart by external forces of
The net difference between the downward compression and tension. It is a measure of how
and upward forces is zero. Put another way, much force is being applied per unit of area of
the forces acting on the K’NEX model are in the material.
equilibrium. Under these conditions, the Stress = Force/Area
K’NEX rectangle is stable.
Strain as a measure of the how far the
2.2. The K’NEX structural members in the molecules of a material are being squeezed
model are squeezed between two external together or pulled apart by the external
forces, one from the student and the other forces of compression or tension. To measure
from the desk. So why is it not squashed? strain, the change in length of the material
It is, by a very small amount. Structural produced by external forces is compared with
members are at their strongest when external its original length.
forces act axially. If these forces do not act Strain = Change in length/Original length
axially then the member will be subjected to
both compressive and tensile forces that may All materials will show a change in length when
cause it to bend, resulting in possible failure put under strain. This change in length may be
of the structure. quite large, as with a rubber band or extremely
small, as in a steel block. When the strain is
Stress in materials removed, the material will return to its original
Every material is made up of atoms and/or length (Reference: Hooke’s Law).
molecules that are packed together. The atoms/
molecules set up internal forces that resist Elasticity as the amount of strain a material will
compression and tension. These internal forces take before it becomes permanently distorted.
are called stresses. Compressive stress Elasticity provides a measure of the stiffness
prevents a material from being squeezed and of a material.
tensile stress prevents it from being stretched
or lengthened. How well a material resists
external forces is a measure of its strength.
44
Skill Builder 3
Teacher’s Notes
Investigating 2-D Shapes - Triangles
INTRODUCTION SAFETY NOTE: Please refer to the beginning

of this Guide for information on the safe use
In this activity students investigate the effects
of forces acting on triangular frame structures.
The activity also offers a context within which
of rubber bands in the classroom. Protective
eyewear should be worn during the activities
to introduce technical vocabulary relating to described below. This is sound safety practice
structures and the forces acting on them. for the science/technology classroom or lab.
OBJECTIVES PROCESS
SECTION I
Students will: WORKING IN GROUPS OF 2-3
• Investigate the effects of external forces on • In this activity the students will carry out a
triangular shapes. simple investigation into the strength of
triangular frame structures. Use simple
• Investigate how triangles are used to make drawings on the board and/or the Student
strong, light structures. Inquiry Worksheets to introduce the
investigations and the vocabulary to be used.
MATERIALS • Explain that a triangle is another example of

• K’NEX Real Bridge Building set(s) a frame structure, made by joining together
a number of parts or members.
• Rubber bands (assorted sizes)
• Ask each group to construct a range of
different sized triangles and to investigate
VOCABULARY what happens when they apply force to the
corners and sides.
stable, unstable, strength of structures, strength
of materials, frame, structure, member, strut,
• Different sized right-angled triangles can be
tie, compression, tension, shear, distort, stress,
made using the components available. The
compressive stress, tensile stress, equilibrium,
students should be encouraged to investigate
lateral applied forces
the effects of forces on triangular shaped
structures by applying a force at (i) the apex
and (ii) the sides.
THE INVESTIGATION
• To make as many different sized triangles
as possible with the available components 1. Vertical Applied Force
and to investigate the effects on them of
external forces.
• Each team selects 3 K’NEX Rods of each kind

and 3 Connectors of each main type.

45
Skill Builder 3
Teacher’s Notes
With a vertically applied force, the triangle’s • Replace the rubber band with a red K’NEX
shape remains the same, demonstrating that Rod and push down again. The sides of the
triangles are strong, rigid structures that do not triangle do not spread apart and the student
distort easily under this type of load. will feel a much stronger reaction force acting
against his/her finger. In this case the internal
2. Lateral Applied Force tension forces produced by the K’NEX Rod
molecules as they resist being forced apart,
equals the tensile stresses produced by load.
In this example:
The total internal

The total downward
external force = reaction force in the
opposite direction
SECTION I
A laterally applied force, however, may cause the

sides of the triangular structure to bend inwards.
Short Rods are better at resisting such bending The sum of the external and internal forces is
forces than long Rods. See Important Safety zero and so the triangle is in equilibrium and
Note: Skill Builder 2. is stable.
• Replacing the base K’NEX Rod with a rubber In reality the tensile strength of a K’NEX Rod
band demonstrates how forces act in a is so large that the joints of the model will
triangular frame structure. We suggest using spring open causing a dramatic failure of
a triangle constructed from 2 yellow Rods, 1 the structure.
red Rod and 3 blue Connectors. A 12.5cm (5”)
rubber band can replace the red Rod by • A rubber band replacing one side can also
hooking its ends over the large gaps in the demonstrate a side under compression.
blue Connectors.
• When a force (load) is applied – in this case

pressing down with a finger at the apex of
the triangle – the apex acts like a hinge and
the two sides spread apart. The rubber band
is stretched and demonstrates that this part
of the structure is under tension. The students
should feel a force pushing back on their
finger. This is the reaction force and is Note: When replacing the K’NEX Rod, the rubber band
produced by the tension forces that are should be under a small amount of tension.
created in the rubber band as its molecules
resist being pulled apart. The force stretching • Ask the students to describe the effects
the rubber band is the tensile stress. of compression on the sides of a triangle
using the correct vocabulary. For example:
compression; compressive stress; equilibrium;
stable; reaction; internal and external forces.
• Extend the activity by asking each pair to

make a short chain of triangles. (Additional
K’NEX Rods and Connectors will be needed).
What happens when external forces are
applied to this structure?
46
Skill Builder 3
Teacher’s Notes
For example: • Now ask your students to find the longest

linear structure they can make using triangles
that will not sag under its own weight or a
small load. It may be easier and faster if
groups simply combine their models together
to make longer bridge sections.
• How does this structure compare to the

simple beam bridge structure they made in
• Students should discover that a framework the Skill Builder #1 Challenge?
or lattice of triangles (also called a truss,)
produces a very strong structure and that
even quite large forces cannot easily distort
its shape. EXPECTED OUTCOMES
Students may be surprised to find that they
SECTION I
Rubber bands replacing the members (shown can build a single span about 1m in length that
above,) can be used to help students visualize remains rigid even when loaded. The beam,
some of the forces acting on this structure. The however, is likely to twist easily because of the
rubber bands should be under slight tension and effects of torsion and may need support. Simply
can be held in position by hooking them round rotating their structure through 90-degrees
the prongs of the blue Connectors. reproduces a long simple beam bridge enabling
the students to compare the two types of
• If one student places one end of their truss structure.
on the edge of a desk and holds the other
end in their hand, their partner can exert a • Can they explain the differences in the
force (load) at the middle of the lower long performance of the two structures?
edge. As the load is applied, the rubber bands
will stretch and pressure can be felt on the • The students should be encouraged to
other partner’s hand. record their observations through drawings,
using directional arrows to indicate
• Ask your students to draw and record those compression
parts of the structure (members) that are and tension ,
under compression and tension when a load and write notes, using the correct technical
is applied to the central section. vocabulary.
For example: WHOLE CLASS

• Review with the students the way in which
the long K’NEX bridges they constructed in
Skill Builder #1 sagged in the middle. You
may want to demonstrate using a selection
of gray K’NEX Rods. Encourage the students
to think about why the structures sagged.
• Gravity acts to pull down on the beam and

makes it bend or sag. (This is in effect the
The broken arrows represent the
reaction of the desk/hand.

47
Skill Builder 3
Teacher’s Notes
weight of the beam, or the dead load.) • Ask: Does making a beam thicker have any
To resist this bending or sagging effect, disadvantages when building a bridge?
compression forces develop in the top and Look for answers that mention (i) adding
tensile forces develop in the bottom sections weight and (ii) adding cost to the structure.
of the beam. A beam will continue to sag until
the forces within it balance the forces due • Explain how a beam can be increased in
to gravity – action and reaction. (Science depth, without significantly increasing its
reference: Balancing Forces/Newton’s Third weight, by using struts and ties to produce
Law of Motion). If the internal forces in the a latticework of triangles called a truss.
beam are greater than the force of gravity, the Trusses use the principle of triangulation
beam retains its stiffness and remains rigid. If, to achieve rigidity in a structure.
however, gravitational forces are greater than
the internal forces in the beam, it will break. A truss structure allows the forces that operate
SECTION I
within it to be distributed across its framework

• Explain how a beam can be made stiffer and enables engineers to make structures rigid
and more rigid by increasing its thickness without making them heavier. By extending the
or depth. truss sideways it is possible to make structures
that are not only long and rigid, but also light
• Demonstrate using equal lengths of different in weight.
sized square section wood/balsa wood or
dowelling. Find and record on the board the • If appropriate you may wish to introduce the
maximum load each piece can support; ask concept of the span-depth ratio as applied
students to plot load against section area and to beams and how it allows engineers to
interpret their results. estimate a suitable thickness for the beam.
(Please refer to Reader #3: Bridges and
Forces 2 for more information on this topic.)
Section Area
Data Table
Section Area Section Area Section Area Section Area
"1" "2" "3" "4"
Maximum load
supported
Maximum load
supported
Square-section area
48
Skill Builder 3
Teacher’s Notes
BACKGROUND RESEARCH AND • http://bridgecontest.usma.edu/tutorial.htm

An excellent web site: The West Point Bridge
INVESTIGATION USING INFORMATION
designer software allows students to design
TECHNOLOGY SOURCES: virtual bridges. (Note: you will need to down
Provide time for the students to explore the load the software first.) Students could then
following web sites: realize their virtual designs using their K’NEX
Real Bridge Building sets.
• “Building Big” at http://www.pbs.org/wgbh/
buildingbig/lab/index.html • Separate groups could construct bridge
This is an excellent site containing “Labs” spans using different truss construction
for students to investigate different types of patterns and compare their load bearing
forces, the effects of forces on shapes and capabilities. Which pattern gives the strongest
materials, and loads on structures. The web structure over the longest span? Did their
site is highly visual and covers many key virtual design behave as expected?
concepts in a simple and effective way.
SECTION I
• Ask the students to select at least one
• www.howstuffworks.com/bridge example of each application and produce
A good general website on bridges, with a short, illustrated report of no more than 250
a helpful section on truss construction. words on how truss construction has been
used in the design of their chosen structure.
• Ask the students to identify the types
materials used in the construction of different
types of bridges and other large structures.
What is the function of the materials they
identify and what forces must the materials
withstand in their named structures? How do
their physical properties make them suitable
materials for their intended function?
• Students could be asked to write a short

report of 200 – 300 words each on: “How
materials/structures behave when subjected
to external forces.”
EXTENSION ACTIVITY
How trusses are used in large structures
• Refer your students to the K’NEX Real
Bridge Building models and building
instructions and Internet web sites
such as www.brantacan.co.uk and
www.howstuffworks.com/bridge to
investigate the advantages of using
trusses in large structures.

49
Skill Builder 4
Teacher’s Notes
Strengthening 2-D Shapes

INTRODUCTION THE INVESTIGATION
T his activity is a progression from Skill
Builder #2: Investigating 2-D Shapes –
Rectangles and Squares and Skill Builder #3:
• To investigate how rectangular frame
structures can be strengthened to resist
compression, tension and shear forces
2-D Shapes – Triangles, in which students use at their corners.
the principle of triangulation to strengthen a
weak frame structure. The activity also offers
a context within which to introduce technical PROCESS
vocabulary relating to structures and the forces
SECTION I
acting on them. WORKING IN GROUPS OF 2-3

• Students select components from their K'NEX
Bridge Building set to make 3 different sized
squares and 1 rectangle.
OBJECTIVES
Students will: • Ask each group to build their K’NEX structures.
• Investigate how rectangular structures can be
reinforced by triangulation. • Review what happens when forces act on a
square/rectangular structure – Skill Builder #2
• Explore how triangulation can involve the use and a triangular structure – Skill Builder #3.
of compression members (struts) and tension
members (ties). • Review their suggestions from Skill Builder #2
as to how the square frame structure can be
strengthened to prevent it being distorted by
MATERIALS external forces. They should be reminded of
• K’NEX Real Bridge Building set(s) the role played by a diagonal brace (in this
case a K’NEX Rod) and should insert one into
• Rubber bands (assorted sizes) their frame structure and then apply external
• String (approximately 30 cm or 12 in) force. (See below: A1, A2 and A3.)
• Paper or light card
• Scissors
• Single-hole punch
A1
VOCABULARY
beam, triangulation, brace, diagonal brace, strut,
tie, compression, tension, members, stable,
unstable, stabilize, strong, rigid, stress, queen
post truss, king post truss, diaphragm
A2
50
Skill Builder 4
Teacher’s Notes
A3
EXPECTED OUTCOMES
• Students should discover that when force WHOLE CLASS
is applied in any of the situations shown • Ask:
above, the structure retains its shape and is • What shapes were present in A, but not
structurally stable. in B?
SECTION I
• How does the inclusion of triangles make
• This diagonal brace/member is called a
an unstable structure, such as a rectangle,
strut when under compression and a tie
stable?
when under tension.
• What forces are acting on the diagonal
• Replacing the base K’NEX Rod with a rubber member in A1, A2, and A3?
band demonstrates how forces act in a
triangular structure. (See Skill Builder #3 • Discuss how rectangular shapes can be made
for additional details.) structurally stable/stronger by triangulation.
Triangulation helps to create rigid structures.
• Students should be encouraged to record
their observations through drawings, using • You may want to discuss and have the
directional arrows to indicate students investigate the designs of the King
compression Post and Queen Post Trusses. They can be
and tension easily made using K’NEX components from
and written notes that incorporate the correct the Real Bridge Building set.
technical vocabulary.
• To remind students of the way in which

rectangles behave when unstable, ask them
to remove the diagonal member and repeat
the activity.
B
Fig. 1: Queen Post Truss
Fig. 2: King Post Truss

51
Skill Builder 4
Teacher’s Notes
• Ask the students to record these shapes in (ii) Construct each side using 1 yellow Rod
their journals and to explain which one is the and 1 blue Rod joined by 1 yellow
more stable structure and why. They should Connector. Complete the triangle by
then build and test the structures by applying adding a gray Connector at the apex.
some force at the corners of the triangles. (iii) Make the central rectangle be adding
2 blue Rods and 1 yellow Rod.
• Suggest they investigate a third design.
Figure 2.
(iv) Build the base using 2 yellow Rods joined
by 1 yellow Connector. At each end add a
light gray Connector.
(v) Construct each side using 2 blue Rods
joined by 1 yellow Connector. Complete
SECTION I
Fig. 3 the triangle by adding a dark gray

Connector at the apex.
SAFETY NOTE: Care should be taken not to (vi) Use a yellow Rod for the vertical column.
apply so much pressure that the Rods are
pushed out of their Connectors. Figure 3.
(vii) Using Figure 2, add 2 blue Rods.
• Building and testing these structures will show
that Fig.1 exhibits some instability. The central
part is an un-braced rectangle. Fig. 2, on the WORKING IN GROUPS OF 2-3
other hand, is composed entirely of triangles
and is more stable. • Ask each group to replace the K’NEX diagonal
member of their rectangle with a length of
• Explain that triangulation must be used string, test as before and observe what
correctly to create stable structures. happens to the string when forces are applied
Fig. 1 can be made stable (stabilized) by to the structure.
he addition of a diagonal bracing strut.
• Ask: What forces are acting in the structure
How to construct the shapes: and string?
(You may want to have a sample of each figure
pre-made for reference purposes.) Students
will need the following K’NEX pieces from their
Real Bridge Building set:
• 7 yellow Rods C
• 12 blue Rods
• 7 yellow Connectors
• 4 light gray Connectors
• 2 gray Connectors
Students should note:
Figure 1. C: The structure will change shape because
(i) The base is made from 2 blue Rods and string is strong under tension but not
1 yellow Rod (in the middle) joined by under compression.
2 yellow Connectors. At each end add a
light gray Connector.
52
Skill Builder 4
Teacher’s Notes
F: Place the square structure on a flat surface

and insert white Rods verticlly into the holes in
diagonally opposite coner Connectors. Punch
holes at each end of a strip of paper or thin card
D and fit them over 2 white Rods.
D: The structure does not change shape shape

because the forces are acting along the length of
the string.
G
You may want to explain that materials such
SECTION I
as string, rope and steel cabling are strongest
under tension – they have a high tensile
strength.
Having a high tensile strength means a material G: A similar exercise could be carried out with a
can withstand very large stretching loads before sheet of paper cut to the same size as the K’NEX
it breaks. This is the reason why steel cables are flexible square. In this case the paper is acting as
used in suspension and cable-stayed bridges. a tension member.
In this example, once the paper sheet is in place

it acts in the same way as the diagonal members
in A.
E
WHOLE CLASS
Discuss how these methods of reinforcing
structures are used in real structures.
E: The structure will retain its shape because in

whichever direction forces are applied, one of the
EXTENSION ACTIVITY
two string members will be under tension. Applying the concepts
This investigation requires teams of 4-6
students to examine the forces acting on
different parts of a K’NEX Real Bridge structure
while it is supporting a load.
F Because one K’NEX Real Bridge Building set

supports the simultaneous construction of any
two bridges, at any one time 8-12 students can
be involved in the construction of, for

53
Skill Builder 4
Teacher’s Notes
example, the Dames Point Cable-stayed Bridge

from Building Instructions Book 1 and the Firth
of Forth Bridge Rail Bridge from Book 2.
You can print additional copies of the Building
Instructions from the CD-ROM that accompanies
the set.
As part of their investigation students could be

asked to:
• Identify which parts of the structure are under

tension and compression?
• Which members are struts and ties?

SECTION I
• What parts might be removed without affecting

the load bearing ability of the structure?
• Which parts are essential to the load bearing

ability of the structure?
In addition, students could investigate

approved Internet web sites such as
www.brantacan.co.uk and
www.howstuffworks.com/bridge to explore
further the function of structural components
in bridges.
Students should be encouraged to make use of

their Information Technology skills to incorporate
photographs of structures downloaded from
approved Internet web sites into a written report
on their findings. They could also be encouraged
to use a digital camera to record their bridge
loading tests. Reports should be compiled from
at least two web sites and should be restricted
to no more than 500 words.
54
Skill Builder 5
Teacher’s Notes
Making 3-D Frame Structures - Cubes

INTRODUCTION • Appreciate that there are limitations to the
distances a simple beam bridge design
T he 3 activities outlined here continue the
progression from Skill Builders #3 and #4
in which students investigated 2-D shapes and
can span.
the use of triangulation to strengthen rectangular • Practice their planning skills while working
frame structures. In this series of tasks and as a team.
investigations they will explore 3-D frame
structures and investigate the effects of forces
acting on them. In Skill Builder 5C students will:
SECTION I
• Investigate how large structures, such as
Through discussions, maintaining journal notes bridges, apply the concepts explored in Skill
and report writing, the activities offer a context Builders 5A and 5B into their design so as to
within which to introduce technical vocabulary resist structural and environmental forces.
relating to structures and the forces acting
on them. • As part of a group of 4-6, undertake a longer
investigation (total time of 1-1.5 hours) of
There are also opportunities for students to the K’NEX Astoria Bridge model.
develop their Information Technology skills by
using Internet search engines to obtain, evaluate
and collate information for inclusion in a report. MATERIALS
• Building Instructions Booklet
OBJECTIVES
• Rubber bands (assorted sizes)
In Skill Builder 5A students will:
• Investigate how 3-D frame structures can be • String and scissors
reinforced/strengthened using: • Books or weights (10g-1000g)
(a) triangulation • Card
(b) tension members • Top loading/top pan balances – Skill Builder 5B
• Undertake a series of short investigations

(total time 20-30 minutes) working in small
groups of 2-3. VOCABULARY
strength, stability, beam, brace, diagonal,
member, strut, tie, compression, tension, shear,
In Skill Builder 5B students will: torsion, triangulation
• Investigate how long, rigid beams can be
constructed using triangulation.
• Understand that there is a relationship

between rigidity, span and depth of a beam –
the span/depth ratio.

55
Skill Builder 5
Teacher’s Notes
Skill Builder 5A • How did different forces affect rectangular

and square 2-D frame structures?
THE INVESTIGATION
1. To construct a cube from K’NEX materials. • Ask them to predict what they think will
happen to a 3-D square frame structure when
2. To investigate: (a) the load bearing ability these forces are applied.
of a cube structure and (b) the effects of
tension, compression, shear and torsion • Do they expect it to be stronger or behave in
on a 3-D frame structure. the same way as a 2-D square?
• Ask them to explain their answers.

PROCESS
WORKING IN GROUPS OF 2-3
1. USING TRIANGULATION
SECTION I
• Ask the students to select EITHER 12 blue

Rods, 8 blue Connectors and 8 dark gray WORKING IN GROUPS OF 2-3
Connectors OR 12 red Rods and 16 dark gray • Ask each group to test their predictions and
Connectors to make a K’NEX cube as investigate the load bearing ability of their
shown below. cubes by adding books or weights.
NOTE : One K’NEX Real Bridge Building set • What is the largest load the cube can support
contains enough parts to make 5 red cubes and without failing?
3 blue cubes simultaneously.
• Groups should compare the results from the
• You may find it useful to draw this shape on different sized cubes and note the results in
the board for students to interpret. their journals/workbooks.
• Ask the students to apply forces to the sides

of the cube as in Skill Builder #2 activities.
For example:
• This activity requires students to interpret the

drawing of a simple 2-D line drawing and
convert it into a 3-D K’NEX model. Draw
attention to the technique for joining the blue Shear forces
and the dark gray Connectors to form corner
joints. Refer to Page 2 of the Building
Instructions booklet if necessary.
WHOLE CLASS
Review the students’ findings and observations
from Skill Builder #2: Investigating 2-D shapes:
Compression forces
56
Skill Builder 5
Teacher’s Notes
of joint type to be used in large structures is very

important and must take into account the effects
of the different forces that act on it.
IMPORTANT SAFETY NOTE: If the structure

is twisted too much, the joints may snap open
ejecting one or more connecting Rods from
the structure. While this effect demonstrates
a dramatic failure of the structure, students
Tension forces should be instructed not to exert too much force
because of the potential hazard from the ejected
Rods. Protective eyewear should be worn.
SECTION I
WHOLE CLASS
Write questions for discussion on the board
and allow the class time to discuss their
observations within their group.
For example:
• Did the structure behave as predicted?
If not, why not?
Torsion forces • Why did you think the structure would
behave in the way you predicted?
• Ask each group to record whether or not their • How might you make your cubes into
cube behaved as they had expected it to and stronger structures?
their explanations for their observations. They
should use the correct technical vocabulary
in their notes and include drawings, using
directional arrows to indicate
WORKING IN GROUPS 2-3
compression • Ask the students to modify their models by
and tension adding EITHER a gray Rod (for the red cube)
or the yellow Rod (for the blue cube). They
should be encouraged to test their structure
after adding a Rod to one or more faces of the
EXPECTED OUTCOMES cube and then record their findings in their
Students should discover that a cube frame journal.
structure is able to support large loads when
the structure is vertically loaded. The weight of It is not possible for K’NEX Rods to be added
the load acts through the vertical sides – along to all of the faces of the cube – there is a limit to
the long axis of the K’NEX rods (or axially). As the number of places that the Connectors can
demonstrated in Skill Builder #2, K’NEX Rods interlock at one time.
are strong when under compression and so the
K’NEX cube is able to support quite large loads.
Other forces, however, cause the frame to

distort. The weak points are at the fixed joints,
which can snap open and break. The selection

57
Skill Builder 5
Teacher’s Notes
2: USING TENSION MEMBERS

• Explain how large structures are subjected to
environmental forces, such as wind, which
can produce torsion effects in them.
• Ask students to consider the effects of high

winds on structures such as the Astoria, the
Golden Gate, The Dames Point and the
The solid lines show where 2 K’NEX diagonal Sydney Harbour bridges.
members may be added to the structure.
No connection points are available to insert a • Ask them to consider the effect of wind on
diagonal member in the plane shown by the
SECTION I
structures with gaps between their members?

broken line.
You can easily demonstrate the effect of wind
The faces with the added diagonal braces by using an electric fan to blow over/move
have been strengthened by triangulation. a small K’NEX structure or a cardboard box.
Other faces can still be easily distorted. Frame Some of the bridge models with large surface
structures, therefore, make use of triangulation areas, such as the Dames Point Bridge, may
for increased strength and to prevent distortion. be seen to move under such conditions. You
may also want to refer to Chapter 9 in Mario
Salvadori’s The Art of Construction, which
WHOLE CLASS outlines some simple experiments that can be
• Review how frame structures can be undertaken in the classroom to demonstrate
reinforced and strengthened by triangulation. the effects of wind on structures.
Discuss how the addition of K’NEX Rods as
diagonal members increased the rigidity of Skill Builder #4 activities introduced students to
the K’NEX cube structure. the use of tension members to strengthen and
reinforce frame structures.
• Refer students to the K’NEX Real Bridge • Ask each group to use string as tension
Building Instructions and/or built models of members to make their structure more stable.
bridges with through-frame structures such Refer the students to Skill Builder #4
as the Forth Rail Bridge, the Astoria Bridge, examples C, D and E if necessary.
the roadway of the Golden Gate Bridge and
the arch span of the Sydney Harbour Bridge;
ask them to notice how triangulation is used Example: Using tension members.
to produce strong, rigid structures that span
long distances.
• Provide factual background information

by comparing the vital statistics of these
bridges with the longest single span in
Chesapeake Bay Bridge (K’NEX Real Bridge
Building Instructions).
58
Skill Builder 5
Teacher’s Notes
Skill Builder 5B to strengthen the structures to create, for

Extending the Activity - example, a simple Warren truss construction.
Making long beam bridges
THE INVESTIGATION
1. To work in teams to construct a 70cm to
80cm bridge span, using a chain of cubes
or rectangles.
2. The beam bridges made by any two teams • Team A can only use the white Rod as their
will be of different depths or thickness. depth measure.
• Team B should use the yellow Rod as their

depth measure. Team B’s beam should be
THE PROCESS twice the depth of team A’s beam.
SECTION I
WORKING IN PROJECT TEAMS OF 4-6
Time for construction: Approximately 15 minutes. Team A
• Each project team should first be encouraged
to plan how they will construct their beam
bridge. They should consider the human Team B
resources they have available and how to
use them effectively. Students could be
introduced to the idea of developing a simple
flow chart to identify the tasks and the order • Once each beam bridge is completed, it is
in which they must be completed. loaded at its mid-point. The load bearing
ability of each bridge can then be compared.
• Questions to ask: The simplest test is to find the load at which
1. How many K’NEX components will they one or both bridges start to sag or break.
need? They should use their previous
experience of making cubes to estimate • Before starting the test each team should be
quantities. asked to predict the results of the test and
2. How will they plan and organize the the reasons for their prediction. For example,
construction of their beam bridge? Team A’s un-reinforced bridge may support
What parts can be pre-assembled and up to 700gm before failure occurs, whereas
used as sub-assembly units? For example, the reinforced structure may support loads of
joining together yellow Connectors to make around 1Kg.
the bridge joints? Pre-assembly of cubes?
Or if the team is large enough, can they • It may be useful for students to measure the
form two teams of sub-contractors each load on the bridge by placing each end on a
making half a bridge? top loading/top pan balance. Each top pan
balance acts as a bridge pier. The loading on
3. What is the specific job of each team
each pier can be traced as the load moves
member, including final assembly?
from one side of the bridge to the other. This
activity will demonstrate to students that the
• Depending on available time, this activity
loading on each pier is greatest when directly
could be separated into two parts. In the
over each one and at a minimum when in the
first part the beams are not strengthened
middle of the bridge span. The maximum
and in the second part triangulation is used
loading on the beam will be at its mid-point.

59
Skill Builder 5
Teacher’s Notes
IMPORTANT SAFETY NOTE: On failure the INTRODUCTION

joints may snap open ejecting one or more • Working in groups of 4-6, students will
connecting Rods from the structure. While this construct a model of the Astoria Bridge.
effect demonstrates a dramatic failure of the The Astoria Bridge is an example of a truss-
structure, students should be instructed not to cantilever construction.
exert too much force because of the potential
hazard from the ejected Rods. Protective • Students will be expected to apply skills
eyewear should be worn at all times. learned from previous Skill Builder activities.
• Each team will construct, test and observe

WHOLE CLASS what happens to the structure when it is
loaded at different points along its length.
• The students should be given time to evaluate
SECTION I
their own results and those of other teams.

Members from each team should be asked to
give a short presentation on their investigation MATERIALS
and include explanations of their observations. • K’NEX Real Bridge Building set(s)
• Book 2 Building Instructions for the Astoria
• This activity may be used to introduce or Bridge (duplicate copies of the instructions
reinforce the concept of the span/depth ratio can be printed from files on the
as used by structural engineers to estimate accompanying CD-ROM)
the depth of a bridge span for a given
working load. Note: Two models of the Astoria Bridge can be
made simultaneously from 1 K’NEX Real Bridge
• From previous activities – Skill Builder #1 – Building set.
students will be aware that short beams have
a greater load bearing capability than long
beams of the same depth. This activity
extends the application of the concept to ADDITIONAL RESOURCES
truss bridge constructions. • Internet access for students to carry out
research on their selected bridge.
Skill Builder 5C
Applying the Concept - THE PROCESS
Investigating a Real World Structure WORKING IN TEAMS OF 4-6
• Teams apply the planning and sub-assembly
experience they gained in Skill Builder 5B
The following activity may be carried out at this to the construction of the large K’NEX
point or may be incorporated into one of two bridge model.
larger activities such as:
• Once completed they should use the model to
• Section II: Case Study of a Bridge Design investigate, identify and answer the following:
and/or 1. What were the structural engineering
• Section III: Bridge Construction - concepts used in the bridge design and
An Exercise in Teamwork, Planning and how were they applied?
Implementation 2. How does the K’NEX bridge model behave
when loaded in different positions?
60
Skill Builder 5
Teacher’s Notes
3. What happens to the bridge structure 4. Why is the main bridge span slightly arched
when loaded? and not straight? What does the arch add
4. Does any part of the bridge structure to the structural strength of the bridge?
move? How is movement minimized in the 5. What alternative designs were considered
real bridge? for this bridge site and why they were
5. How rigid is the bridge structure? Does it rejected?
twist easily? 6. In your opinion, is the bridge a successful
6. How would you modify the K’NEX bridge structure? Why or why not?
design to prevent the structure twisting?
7. Would you use the K’NEX model design Some useful Internet web sites for the
to make a full-scale construction? Explain Astoria Bridge:
SECTION I
your reasons.
8. How does the construction of your K’NEX This is a useful web site for the Astoria Bridge.
bridge model compare with that of the real
bridge? Use photographs obtained from the http://www.oldoregon.com/visitor-info/entry/
Internet and from the Building Instructions. astoria-megler-bridge/
• Each member of the team should write his/her You can obtain additional resources by entering
own report on the bridge design. The report Astoria Bridge – Oregon in a search engine.
should include a description of the practical
investigations and how the behavior of the
model differs from that of the real bridge.
• As part of their record keeping, students

could be asked to make scale drawings of
their K’NEX Real Bridge model from direct
measurements made on the actual model.
If time permits, the drawings could include
a plan as well as side and front elevations.
• Students might carry out an Internet

investigation on the Astoria Bridge using
some of the links provided below. These offer
some additional statistics and photographs
with which to analyze its construction.
Possible topics to investigate:
1. What challenges of location faced the

designer of the bridge and how were
they overcome?
2. What types of forces act on the bridge
and how does the design takes them
into account?
3. Why was this particular type of bridge
design chosen for this location?

61
Skill Builder 6
Teacher’s Notes
Spanning Gaps - Beams or Arches?

INTRODUCTION VOCABULARy
T he concepts and activities outlined here
continue the progression from those in
Skill Builder #5 and introduce students to the
load, strength, stability, beam, arch, brace,
diagonal, member, strut, tie, compression,
tension, shear, torsion, triangulation, span,
effects of external forces on two bridge designs. pier, guardrail, abutments, arch
In Skill Builder #6 students compare and contrast
a simple beam bridge with an arch bridge.
As in previous Skill Builder activities, technical
vocabulary can be introduced and students
THE INVESTIGATION
SECTION I
have the opportunity to develop their Information This is in two parts:

Technology skills. 1. Beams and arches:
Students, working in small groups of 2-3,
investigate the load bearing ability of two
different bridge designs: (a) a simple beam
OBJECTIVES and (b) an arch. Students will carry out a
Students will understand that: series of brief investigations, (20-30 minutes
• The practical length of a beam bridge is total time,) using a 500g load at the mid-point
limited, but an arch structure is stronger and of each model bridge and measuring the
can be used to span greater distances. amount of sag in the beam or arch. The
simple beam bridge will be a modified version
• Simple beam bridges are subjected to bending of one span of the K’NEX Chesapeake Bay
forces due to tension and compression. Bridge. Introducing the arch concept will
involve using a section of black decking from
• The predominant force acting on an arch the set and experiencing the forces involved
structure is compression. in the structure.
• The physical characteristics of the site and the 2. Applying the concepts:
intended use, affects the design of a bridge. The second part, involving larger teams of
4 to 6 students, investigates how structural
engineers have used the simple beam and
arch concepts to make real bridges. Students
MATERIALS will construct and test K’NEX models of the
• K’NEX Real Bridge Building set(s) Chesapeake Bay Bridge and the Sydney
• Building Instructions Booklet Harbour Bridge. This investigation also
provides opportunities for students to carry
• Rulers
out research using an approved Internet
• Slotted or other masses (10g-1000g) search engine.
• Sheets of white paper
Total time: 1.5 - 2 hours
• Additional copies of Building Instructions for
the Chesapeake Bay Bridge and the
Sydney Harbour Bridge models.
• Top pan balances (optional for Part 2)
62
Skill Builder 6
Teacher’s Notes
PROCESS • They should compare the maximum load,

amount of sag in the beam and amount of
1. Beams and Arches splaying of the piers (if any).
(a) A simple beam bridge
• The students should be encouraged to
• Ask the students to recall their first attempts
record their observations through the use
at constructing a bridge to span a gap. These
labeled drawings and directional arrows,
attempts were probably not very successful as
where appropriate. Notes should be included
they sagged in the middle, often before a live
using the correct technical vocabulary.
load was placed on the structure. Review the
ways that such structures can be strengthened:
using triangulation to create truss structures,
for example. WHOLE CLASS
Discuss the effect of increasing the length,
SECTION I
• Explain that in this Skill Builder activity they without additional support, on the load bearing
will first investigate an alternative way of ability of a simple beam bridge. Raise the issue
strengthening a long simple beam bridge. of the limitations that a simple beam bridge
Ask them to look at the photo of the presents when spanning wider barriers.
Chesapeake Bay Bridge-Tunnel shown on
P. 4 of Book 1 Building Instructions. Ask what
they notice about the characteristic features
of the bridge. How long is this bridge? Would (b) An arch
an unsupported structure be able to span WORKING IN GROUPS OF 2-3
this distance? • For this activity each group will need 1 piece
of black decking from the K’NEX Real Bridge
• Review how engineers have used piers to Building set and access to weights. Explain
support the structure – in effect they have that they will compare the load bearing
built a very large number of simple beam capacity of a simple beam and an arch. They
bridges and connected them to create a will also experience the forces acting on the
continuous span. arch as they manipulate the length of decking.
• Ask them to gently bend the piece of decking

WORKING IN GROUPS OF 4-6 into an arch shape. They should place their
• Half the team will build 2 sections of the hands on the desktop as they hold the shape
Chesapeake Bay Bridge while the other half in position and then relax their hold slightly.
will build the equivalent length, but without Ask:
the extra set of piers. • What do they feel?
• What happens to the arch once the
• Students will then place their model beam pressure from their hands is released?
bridges so that the piers are resting on sheets They should feel the two ends of the arch
of paper. They should draw the footprint of pushing outwards against their hands. To
the piers on the paper. maintain the arch shape they have to push
inwards. Students should take turns trying
• Ask them to add loads, incrementally, to this activity.
their bridges and notice what happens to the
decking and to the position of the piers. • To compare the load bearing capacity of a
simple beam with an arch, ask the students to
carefully add a 500g weight to the mid-point

63
Skill Builder 6
Teacher’s Notes
of the arched roadway. One student can hold

the ends of the arch in place, while a second
student adds the load. Ask them:
• To record any evidence of the arch sagging
or showing signs of failure.
• What happens to the arms of the arch as the
load is increased?
• What must they do to enable the arch to
keep its shape?
• What will happen to the arch if they
removed their hands?
• Can the arch support a 1Kg load?
SECTION I
• The students should then undertake a similar

investigation using the roadway as a beam
and compare their results. It can be supported
at either end on books or students can use
the piers they made in the first part of the
activity. They should be asked to load the
beam at its mid-point with a 500g weight
and record their observations. What is the
maximum load the beam can support?
Once this part of their investigation is completed,

groups should be given time to record their re-
sults and explain their findings.
• When designing a bridge or structure,
engineers try to eliminate a combination of
WHOLE CLASS compression and tension acting together in
• Discuss the results of the two different any structural member as this can lead to it
bridge investigations. bending. The result of a member bending
could be the whole structure fails.
• This may be a good point to review or
introduce the different types of forces acting • Materials are strong or weak when acted on
in and on beam and arch bridges, and the by tensile stresses or compressive stresses.
advantages and disadvantages of each design. By designing a structure so that members are
Alternatively, direct the students to the only under compression (struts) or tension
Readers #2, 3 and 4. (ties), bending effects can be greatly reduced.
• Facts to highlight: • Arch bridges are stronger than beam bridges

(i) Beam bridges are subjected to the because the whole structure is under
forces of tension and compression. compression. External load forces acting on
(ii) The ability of a beam bridge to resist the arch are dissipated along the curved
bending forces depends on the stiffness arms towards its ends and from there into
of the material from which it is made. the supporting sides. The reaction of the
supporting sides is to push back against the
(iii) The predominant force in an arch is
compression.
64
Skill Builder 6
Teacher’s Notes
arch creating a resistance that is transferred PART 2: APPLYING THE

along its length. All parts of the arch bridge
are therefore under compression – from the
CONCEPT - INVESTIGATING REAL
weight of the bridge deck pushing out along WORLD STRUCTURES
the curve of the arch and from the resistance
of the sides pushing back. Tension, by
INTRODUCTION
comparison is a very minor force in an arch, • Teams of up to 6 students construct a K’NEX
even on its underside. Bridge model of either the Chesapeake Bay
Bridge or the Sydney Harbour Bridge. They
• Early arch bridges were made from stone – will be expected to apply skills learned from
a material that is strong under compression. previous Skill Builder activities.
Many Roman arch structures are still standing
today and were made without mortar – a • Students should be made aware that although
testimony to the inherent structural strength the total length of the Chesapeake Bay
SECTION I
of the arch. The only things holding the blocks Bridge-Tunnel is approximately 24,140 m
together are the compression forces acting in (15 miles), the longest single bridge span is
the structure and the ability of stone to resist only 31m (102 ft). By comparison the single
compression. Arch bridges, however, need span of the Sydney Harbour Bridge is 504 m
strong supporting structures – abutments – long (1663 ft).
to keep the sides in place and so prevent the
arch from collapsing. • Two bridge models can be made
simultaneously from a K’NEX Real Bridge
• Remind the students of what occurred when Building set. Once teams have completed
they removed their hands from the sides of investigating their own bridge, they could
the arch in their initial investigation (P. 63). change places with another team and
Their hands had been acting as abutments. investigate the other bridge design.
Questions to ask:
• Where and at what types of locations/sites
are beam and arch bridges used? OBJECTIVES
• Why do the designs suit their particular For students to learn:
situations? • How location, site and intended use affects
the design of a bridge.
• Refer the students to the examples in the
K’NEX Real Bridge Building set – the • How arches are used in bridge designs.
Chesapeake Bay Bridge-Tunnel and the
Sydney Harbour Bridge. • The forces that act on beam and arch
structures.
The following activity may be undertaken at

this point or may be incorporated into one of
two larger activities such as:
ADDITIONAL RESOURCES
• Internet access for students to carry out
Section II: Case Study of A Bridge Design research on their selected bridge.
and/or
Section III: Bridge Construction –
An Exercise in Teamwork, Planning and
Implementation

65
Skill Builder 6
Teacher’s Notes
THE INVESTIGATION • Does any part of the bridge structure move?

• Each student team will construct, test and What causes this movement in the structure?
observe what happens to the structure when How is any similar movement prevented in the
it is loaded at different points along its length real bridge?
and identify the forces that act on it. K’NEX models are not anchored in any way
and so movement is likely to occur in the
• They will also research: bridge piers or, in the case of the arch, where
• The structural engineering concepts used the abutments would normally be. The
in the design and how they were applied. strength of any arch structure is found in the
• How the design has been influenced by the reaction of the abutments to the outward
physical characteristics of the site. horizontal forces produced by the arch. Refer
students to the web sites listed below to find
out how construction of the real bridges
reduced structural movement.
THE PROCESS
SECTION I
WORKING IN TEAMS OF 4-6 • As part of their record keeping, students

• Teams should spend time considering the could be asked to make scale drawings
most efficient way to construct the bridge of their K’NEX Real Bridge from direct
and to locate the background information measurements made on the actual model.
needed for their investigation. They should If time permits, the drawings could include a
also discuss how they might measure the load plan together with side and front elevations.
on the bridge and how to record movement in
the structure of the bridge when it is loaded. • The following questions could be asked of
the teams:
• When investigating how their K’NEX bridge • Would you use the K’NEX model design
model behaves when loaded in different to make a full-scale construction? Explain
positions, it may be useful for students to your reasons.
measure the load on the bridge by placing • Compare the construction of your K’NEX
each pier on a top pan balance. The loading bridge model with the real bridge. Use
on each pier can be traced as the load moves photographs obtained from approved
from one side of the bridge to the other. This Internet web sites.
activity will demonstrate to students that the
loading on each pier is greatest when directly • Team members might carry out an Internet
over each one and least when in the middle of investigation on the two named bridges using
the bridge span. The maximum loading on the some of the links below. These websites
beam will be at its mid-point. provide additional facts, statistics and
photographs with which to analyze the
• Students should be encouraged to determine bridge construction. Possible areas to
the maximum load each bridge can hold on a research include:
single span. They should note where and how • Design challenges caused by the physical
any failure in the structure occurs. conditions of the site and how they
were solved.
• They should consider what forces are acting • The types of forces acting on the bridge
on their model when it is under load and how and how the design accounts for them.
the bridge is affected.
• The challenges facing the construction
team and how they were solved.
66
Skill Builder 6
Teacher’s Notes
• Why this particular type of bridge design WHOLE CLASS

was chosen for this location. Review the students’ findings on:
• The alternative designs that were • How the two model bridges behaved
considered and why they were rejected. when loaded.
• If, in their opinion, the bridge is a successful • How each real bridge design was affected
structure. They should be prepared to justify by the loads they must support, the
their answers. distances they have to span and the
nature of the bridges’ locations.
Information on the Chesapeake Bay
Bridge-Tunnel can be found at:
http://www.cbbt.com/history.html ASSESSMENT
This site outlines the history of the Chesapeake
• Each member of the team should write a
Bay Bridge-Tunnel and shows photographs of its
SECTION I
report on the two bridge designs to include
construction.
the group’s practical investigations and how
the behavior of each model differs from their
http://www.pbs.org/wgbh/buildingbig/
real world counterparts.
wonder/structure/chesapeake_bay_brdg.html
Useful background information and statistics.
http://www.roadstothefuture.com/CBBT.html
Helpful information, links to other sites and
photographs of the bridge.
Information of the Sydney Harbour Bridge

can be found by visiting the following sites:
http://www.gids.nl/sydney/info.html
http://www.austehc.unimelb.edu.au/tia/
426.html Both sites give some interesting
information about the construction of the bridge.
http://www.bridgepros.com/projects/
SydneyHarbour/SydneyHarbour.htm This site
also provides links to similar arch bridges in other
parts of the world.
These sites were obtained from search engines

using key words such as, “Chesapeake Bay
Bridge Tunnel.”

67
Skill Builder 7
Teacher’s Notes
Investigating Cantilevers
INTRODUCTION The forces exerted on the root are dependant

on the size of the load (measured in Newtons)
T he investigations carried out so far have
involved simple beams. Beams are structural
members that are subject to bending forces, so
and the distance the load is applied from the
root (measured in meters). This turning force
that a simple beam supported at both ends is called the bending moment and can be
tends to bend in the middle. calculated as follows:
A cantilever is a beam that is supported at The bending

Force Distance
one end only. An example that most students moment = X
SECTION I
(Newtons) (meters)
can visualize at work is that of a diving board. (Newton meters)
A board with no load remains straight, but as the
diver moves to the free end of a springboard it
will bend downward. As in previous Skill Builder activities, there are
opportunities to introduce technical vocabulary
The cantilever principle is used in bridge and for students to develop their Information
construction as well as in a wide range of Technology skills using Internet search engines,
other structures, including sports stadium to obtain, evaluate and collate information for
roofs, balconies, carports, aircraft wings, inclusion in a report.
shelves, hinged doors and castle drawbridges.
One of the main limitations in making arched
bridges is that both sides of the arch act as OBJECTIVES
cantilevers until the span is completed. You
For students to learn:
may want students to research how cantilevers
• Cantilever beam bridges are subjected
influenced the construction of the Sydney
to bending forces due to tension and
Harbour Bridge. Cantilevers can also be seen
compression.
in nature – tree branches or human arms and
legs, for example.
• In cantilevers, tensile forces act on the
upper surface and compressive forces on
Two types of basic cantilevers are used in bridge
the lower surface.
designs:
1: Hinged cantilever: Tower Bridge. The beam
• How cantilevers are used in the design
is attached to a support by a hinge joint, which
of bridges.
allows the beam to rotate around the hinge.
2: Fixed cantilever: Firth of Forth Rail Bridge,

Astoria Bridge and cable-stayed bridges such
as The Dames Point Bridge. The beam is fixed
to its support in such a way that it is unable
to rotate. A load placed on the free end of
the beam tries to make the beam rotate in the
direction of the applied force, but because
the fixed end (or root) cannot rotate, the beam
bends downwards instead.
68
Skill Builder 7
Teacher’s Notes
MATERIALS PART 1:
• K’NEX Real Bridge Building set(s) INVESTIGATING A CANTILEVER
• Building Instructions Booklet - you will
need additional copies printed from the
THE PROCESS
accompanying CD-ROM WHOLE CLASS
• Slotted masses (100g) • Introduce the class to the concept of a
cantilever in action by asking them to hold
• Spring scales
the end of a length of black decking from
• String the K’NEX Real Bridge Building set (or a ruler)
• Rulers between their thumb and forefingers. Holding
it firmly with some pressure will make sure
• Top pan balances (optional) that the ‘beam’ remains level, but as soon as
they release the pressure it will start to bend
SECTION I
downwards.
VOCABULARY
cantilever, fixed and hinged cantilevers, root, • Adding a weight at the free end will help them
bending moment, load, strength, stability, understand how even more force must be
beam, brace, diagonal, member, strut, tie, applied to keep the beam level.
compression, tension
• Suggest they place the beam on an upright
book so that most of it is unsupported and
THE INVESTIGATION then find a way to make it balance. They
could then add a weight at the free end and
This is in two parts: then try to balance the beam again.
1. Investigating a cantilever
The cantilever will be made by modifying the • Explain that this is the principle of the
bridge raising mechanism from the K’NEX cantilever – the beam can extend unsupported
Tower Bridge model in Book 1, Page 41: for a considerable distance so long as at
Steps 24 – 28. One modification in Step 24 the opposite end there is a means to
is to replace the white Rods with gray counterbalance it.
Rods. This modification will help to multiply
the forces acting on the structure. Two • Explain that they will build a model of a hinged
mechanisms can be made from each cantilever and test its load bearing ability by
bridge model so that 4 groups of students observing the deflection or bend in the beam
(2-3) can work from 1 Real Bridge Building caused by placing a 100g load at its free end.
set simultaneously. They will then measure the force required to
Time: 30-40 minutes. raise the beam back to a horizontal position
by pulling back on the blue lever mechanism
2. Investigating how structural engineers of the model.
have used cantilevers to make real bridges
This will involve teams of 4-6 students Students can EITHER observe “cause and
constructing and testing K’NEX bridge models effect” and “feel” the forces needed OR make
that use the cantilever concept in their design. measurements of the deflection at the end of
This investigation also provides opportunities the beam and the forces, using a spring scale.
for students to carry out research using an
approved Internet search engine such as • Explain that they will investigate how longer
Google. lengths of the cantilever beam behave.
Total time: 1.5 – 2 hours.

69
Skill Builder 7
Teacher’s Notes
Increasing the length of the cantilever can For example:

be accomplished by inserting additional blue • What do they think might happen to the
Rods and yellow Connectors into the beam at cantilever beam as its length increases?
the hinged end. • What will be the effect on the vertical
support?
• You may want to discuss some of the technical
vocabulary at this point, such as free end, • What is the longest length of cantilever
root, bending moment/turning force and beam (not the vertical support) that can
introduce the mathematical equation used to support a 100g load without bending?
derive the bending moment (see above). • How will they measure the amount of
deflection of the cantilever beam and how
• The starting point for loading the cantilever will they record and present their results to
beam should be as close to the hinge (root) as make them easier to interpret?
possible. You may want to make a drawing on
SECTION I
• What position of the load maximizes the

the board similar to the one shown below. stresses on the cantilever beam?
Observations to be made are:
• Length of cantilever beam (L) • Did their bridge behave as they expected?
• Deflection at the free end of the beam (D) • Groups should be given time to record their
• Force required to return the main part of results and explanations of their findings,
the beam to a horizontal position (F) using the correct technical vocabulary,
• The effect of the cantilever beam on the before proceeding to the next part of the
vertical support. (S) activity. Drawings of models should also be
made – these should include descriptions
of the forces acting on the main parts of
L F the structure.
D
S
WHOLE CLASS
• Allow time for the class to discuss
their findings and provide explanations of
their observations.
WORKING IN GROUPS OF 2-3 • Ask how a long cantilever beam can be

• Allow students a few moments to familiarize supported to make a stronger structure.
themselves with the building instructions for What techniques have they used before to
the bridge raising mechanism of the Tower strengthen weak structures and how can
Bridge model, the changes to be made and they be applied here?
what they have to do.
• Once built, provide time for them to EXPECTED OUTCOMES

investigate the model before starting their • Students might be expected to find that as
investigations. They can discuss and the length of the cantilever beam increases,
comment on how they think the cantilever the bending moment also increases. The
will behave. maximum stresses occur in a cantilever beam
when a live load is placed at its free end and
they are minimal when the load is close to the
hinge or root.
70
Skill Builder 7
Teacher’s Notes
Compression and tension in a cantilever Use the extended beam length (made by
beam can be demonstrated using a length adding blue Rods and white Connectors) and
of sponge graduated vertically into equal incorporate a red Rod as a strut. The upper
spaces. As the sponge cantilever bends, the part of the Rod can be connected to a yellow
segments on the top become wider indicating Connector, while the lower end can simply rest
tension and those on the bottom decrease in in the angle.
size indication compression. For example:
SECTION I
• The weight of the beam itself (the dead load)
also has a significant impact on cantilever
bridge design. The K’NEX model should
demonstrate that the vertical support is also
subjected to bending forces. Using string as a tension member or tie.
DEMONSTRATION WHOLE CLASS

• Discuss and demonstrate how a cantilever • Two discussion points can be raised.
beam can be supported either by pushing up 1. The need for a tall tower to give enough
from below and/or pulling up from above. height for a tension member to be used.
2. A long cantilever puts bending forces
• Each group should then try for themselves. on the vertical support. How can this
be avoided?
• You may wish to review the need for balanced

WORKING IN GROUPS OF 2-3 forces within structures and how this might
For example: be achieved.
For example:
By joining two structures so the forces are
equal and opposite:
Add red Rod here

71
Skill Builder 7
Teacher’s Notes
This arrangement balances the bending forces PART 2: APPLYING THE

on the vertical support. Two models can be
simply joined together using Connectors. CONCEPT - INVESTIGATING
REAL WORLD STRUCTURES
INTRODUCTION
• Teams of up to 6 students construct a
K’NEX Bridge model of either the Firth of
Forth Rail Bridge or the Dames Point Bridge.
They will be expected to apply skills learned
from previous Skill Builder activities.
Here the two arms push against each other
SECTION I
and are similar to the two halves of an arch. NOTE: Although the Dames Point Bridge is
classified as a cable-stayed bridge, its design
contains both cantilever and suspension
WORKING IN GROUPS OF 4-6 bridge elements.
• Ask 2 groups of students to combine and
• Two K’NEX Real Bridges can be made
use both models to investigate the situations
simultaneously from a K’NEX Real Bridge
outlined above.
Building set. Once a team has completed
investigating their own bridge, they could
• At the completion of this part of their
exchange places and investigate the other
investigation, groups should be given time
bridge design.
to record their results and explanations of
their findings. Drawings of models should
include descriptions of the forces acting on
the main parts of the structure. OBJECTIVES
For students to learn:
• How location, site and intended use affects
the design of a bridge.
• How cantilevers are used in bridge design.

this point, or may be incorporated into one of ADDITIONAL RESOURCES
two larger activities such as: Access to the Internet to carry out research on
each group’s selected bridge.
Section II: Case Study of a Bridge Design
and/or
Section III: Bridge Construction – THE INVESTIGATION
An Exercise in Teamwork, Planning and • Each student team will construct, test and
Implementation observe what happens to the structure when
it is loaded at different points along its length
and identify the forces that act on it.
72
Skill Builder 7
Teacher’s Notes
• They will also research: • In their investigation of the Firth of Forth Rail
• The structural engineering concepts used in Bridge students should be asked to identify
the design and how they were applied. the main structural members that are under
• How the design has been influenced by the compression and tension. What happens if
physical characteristics of the site. members are removed from A or B?
A
THE PROCESS
• Combine 2 groups to act as a single team to
construct a K’NEX bridge model and then to
SECTION I
investigate and identify, for example: B
• How their K’NEX Bridge model behaves

when loaded in different positions. • In previous Skill Builder activities students
• Suggest that before teams join the halves learned how struts and ties are strongest
of the bridge together, they should test when forces are applied axially. When not
what happens when a small load is placed applied axially, struts can bend and buckle.
on one side. Can the students identify how the bridge
designer has braced long structural members
• What forces are acting on their model when to prevent the buckling and collapse of
it is under load and how do they affect it? the structure?
Do parts of the model move? How are
these potentially disastrous problems • It may be useful for students to measure the
solved in the real bridge structure? load on the bridge by placing each pier on a
top pan balance. The loading on each pier
• In their investigation of the Dames Point can be traced as the load moves from one
Bridge, student teams might replace some of side of the bridge to the other. This activity
the longer cables with string or long elastic will demonstrate to students that the loading
bands to help visualize the tension that on each pier is greatest when directly over
occurs when the structure is loaded. each one and at a minimum when in the
middle of the bridge span. The maximum
• In the completed bridge, the outer cables loading on the beam will be at its mid-point.
could be disconnected to see what happens
to the structure when a large load is placed in • Does any part of the bridge structure move?
the middle of the main span. The bridge will in What causes this movement in the structure?
fact collapse in on itself because the forces How is this type of movement prevented in
are no longer balanced. the real bridge?
• As part of their record keeping, students • K’NEX models are not anchored in any way
could be asked to make scale drawings and so movement is likely to occur in the
of their K’NEX Real Bridge from direct bridge piers. Refer students to the web sites
measurements made on the actual model. listed below to find out how construction of
If time permits, the drawings could include the real bridges prevented such movements.
a plan as well as side and front elevations.

73
Skill Builder 7
Teacher’s Notes
• You may want students to provide answers to • The alternative designs that were
the following: considered and why they were rejected;
• What is the maximum load each bridge can • If, in their opinion, the bridge is a successful
hold on a single span? Note where and structure. They should be prepared to justify
how any failure in the structure occurs. their opinions.
• Would you use the K’NEX model design to
make a full-scale construction? Explain The following general Internet web sites are
your reasons. useful for student research and photographs.
• Compare the construction of your K’NEX www.howstuffworks.com
bridge model with the real bridge. Use www.brantacan.co.uk
photographs obtained from approved http://encyclopedia.thefreedictionary.com/
Internet web sites. Cable-stayed%20bridge
Firth of Forth Rail Bridge web sites:

SECTION I
• Photographs of a cantilever bridge collapse,

the Koror-Babeldaob Bridge may be seen on: http://www.pbs.org/wgbh/buildingbig/
http://www.ketchum.org/bridgecollapse.html. wonder/structure/firth_of_forth.html
• Students might carry out an Internet http://www.pre-engineering.com/resources/

investigation on the two named bridges forth/forthbridge.htm
using some of the links below. These provide
additional facts, statistics and photographs Dames Point Bridge web sites:
with which to analyze its construction. http://www.bridgepros.com/projects/
Some topics to research: DamesPoint/DamesPoint.htm
• Design challenges caused by the physical
conditions of the site and how they
were solved. WHOLE CLASS
• The types of forces acting on the bridge Review the students’ findings on:
and how the design takes them into account. • How the two bridges behaved when loaded.
• Why this particular type of bridge design was • The way in which each bridge design was
chosen for this location. affected by the loads they must support,
the distances they have to span and the
• Both bridges are like giant seesaws. nature of the their locations.
How does the bridge design take into account
loads moving across them?
• The challenges facing the bridge construction ASSESSMENT
team and how they were solved.
• Each student should write a personal report
• Why is the main bridge span of the on the bridge designs that includes the
Dames Point Bridge slightly arched and not group’s practical investigations and how the
straight? What does the arch add to the behavior of each model differs from their real
structural strength of the bridge? world counterparts.
74
Skill Builder 8
Teacher’s Notes
Investigating Suspension Bridges
INTRODUCTION • Additional string for hangers (NOTE: String is

available in the K’NEX Real Bridge Building
In this Skill Builder students are asked to
investigate the technology of suspension
bridges. This will be the culmination of their
set but should not be cut.)
• Small masses (200g – 500g)
exploration into the ways in which engineers • Spring scale (optional)
have overcome the problem of spanning wider
and wider barriers.
VOCABULARY
SECTION I
The activities also present opportunities for
students to continue developing their technical Simply supported beam bridge, span, gap,
vocabulary, identifying and solving simple cable, hanger, tower, compression, tension,
problems, keeping journal notes and writing bending, dead load, live load, compressive
reports. They will also be expected to expand stress, tensile stress, front elevation,
their Information Technology skills through side elevation
the use of word processing and/or desk top
publishing, digital cameras to help record
information otherwise difficult to save, the THE INVESTIGATION
Internet for research, and presentation software
for report writing. This is in two parts:
1. Investigating a simple suspension
bridge model:
In this investigation students work in teams
OBJECTIVES of 4-6, to make and investigate a simple
For students to learn: suspension bridge model.
• Suspension bridges are subject to
compression and tension forces. They will review what happens to a long,
simply supported beam bridge and how the
• Towers must be subjected to axial suspension bridge design helps solve some
compression, cables and hangers to tension. of the problems associated with making
long beams rigid. This will involve them
• An imbalance of tension and compression in comparing the solution developed by the
a structural member causes bending. engineers responsible for the design of the
Chesapeake Bay Bridge-Tunnel with that
• Simple problem solving skills. developed for a suspension bridge such as
the Golden Gate Bridge.
Time: 45 minutes
MATERIALS 2. Investigating how structural engineers
• K’NEX Real Bridge Building set(s) have solved some of the problems
• Building Instructions identified in Part 1 through the examination
of a real world suspension bridge:
• Scissors
Continuing to work as part of a larger group,
students investigate how structural

75
Skill Builder 8
Teacher’s Notes
engineers have solved some of the problems attached to the Tower by passing the ends
identified in the first part of their Skill Builder of Rods forming the beam through the holes
activity. They will continue to construct and in the yellow Connectors. Some black Clips
then test their K’NEX Real Bridge model of can be added to keep the Rods in place.
the Golden Gate suspension bridge. This
activity also provides opportunities for
students to carry out research using an
approved Internet search engine.
Time: 1.5 hours
PART 1: INVESTIGATING A
SECTION I
SIMPLE SUSPENSION BRIDGE

THE PROCESS
WHOLE CLASS
• Review the different types of technologies
that have been used to span wider and wider
barriers – piers, trusses, arches, cantilevers.
Explain that the students will investigate the WORKING IN GROUPS 4-6
suspension bridge, which is essentially a • Allow the students a few minutes to familiarize
beam bridge with a large amount of additional themselves with their task and to plan how
support. This support allows suspension they will make their model.
bridges to span barriers of more than 3000
meters, compared to the simple beam bridge Suggested sub-assemblies for a group of
with its maximum span of 100 meters. 5 students:
Steps 1-5 x 2;
• Explain that they will begin by creating a Steps 6-7 (with modification) x 2
simple model of a suspension bridge. They Steps 8-11 x 2
will follow the Building Instructions for the
towers of the Golden Gate Bridge (Book 2, Steps 12-14 x 2
Pages 35-40: Steps 1-14) with a minor Beam x 1
modification. They will also be required to
construct a simple beam for the bridge. • Constructing the bridge – groups should ask
Any length of Rod may be used to achieve themselves the following:
the length of 120cm, but it is recommended • Who will make the towers?
that the width of the beam is one blue Rod. • Who will make the beam?
Yellow Connectors can be used for joining
the beam components. • Does everyone in the group understand
what they are expected to do?
• Tower Modification: In Step 7 a green Rod • How many K’NEX components will be
should be inserted on either side of the needed to make a beam 120cm long?
uppermost yellow Connector. Then another
yellow Connector is added on either side so • The 120cm beam is intended to simulate
that there are 3 yellow Connectors in a row, the long single spans used in suspension
joined by green Rods. The beam can then be bridge design.
76
Skill Builder 8
Teacher’s Notes
• Students work in their teams to investigate • The towers are effectively behaving like
the forces that must be accounted for when vertical cantilevers and are being subjected
designing suspension bridges. First, they will to considerable bending forces, as is
attached their beam to the towers, making the beam.
use of the modification to the towers noted
above, and then notice what happens when • You may wish to discuss how structural
a load is added to this long, simply engineers try to avoid the weakening effects
supported beam. of bending (when a structural member may
be subjected to excessive tension and
• Ask them to consider how they might compression forces).
overcome the problems they observe. Would
a cable-stayed solution work for a very long • Engineers try to design structures in which
beam bridge? the compressive and tensile stresses that
act on a structure are focused along lines of
SECTION I
• Students may have had experience of strength. For example, in beams and columns
cable-stayed bridge design. This simple – axial compressive force and in cables –
activity is also intended to demonstrate that tensile compressive forces.
over such a long span, the cable-stayed
solution is not a practical option and there • Suspending the bridge:
are limitations on the use of that design for In this part of the activity, the student teams
very long single spans. create a simple suspension bridge. They
should use the string from the K’NEX
• Ask: Real Bridge Building set as the main cable
• Is simply attaching a cable to the tops of and other pieces of non-K’NEX string can be
the towers and suspending the beam from cut to length as the hangers.
it the solution?
• What do the students think will happen? • Even when supported by a single hanger at its
mid-point, the beam halves may still show a
• Try it and see what occurs. small deflection, with or without a small load.
• What alternative designs can the students
suggest? • Additional hangers will be needed to fully
support the beam along its length. Adding
• Once this stage of construction is complete, more hangers to the bridge makes the beam
groups should be given time to discuss increasingly rigid.
the problems they encountered with their
structure and then record their observations, • By pulling on both ends of the main cable,
with explanations. A digital camera may be students can experience the forces needed to
useful to help students record information support the dead load of the bridge and any
that is otherwise difficult to retain. live load it is carrying.
• In addition, they should also note the need

for the main cables to be strongly anchored.
EXPECTED OUTCOMES In their model, they perform the role of the
• The students will find that the beam will anchorages, but how is this accomplished on
continue to bend as before but with the a real world suspension bridge?
added effect of the towers being pulled
inwards. • Ask what might happen to the Golden Gate
Bridge if one of the main cables broke?

77
Skill Builder 8
Teacher’s Notes
• Students should also note the towers do PART 2: APPLYING THE CONCEPT -
not bend. They should able to identify the
compressive and tensile stresses acting on
INVESTIGATING REAL WORLD
the cables and towers and explain how the STRUCTURES
materials from which they are made behave INTRODUCTION
when subjected to these stresses.
• In this activity the teams complete and then
investigate their model of the Golden Gate
• At the completion of this part of their
Bridge, applying skills learned from previous
investigation, groups should be given time to
Skill Builder activities.
complete the recording of their results and
their explanations before proceeding to the
• Two K’NEX Real Bridge models can be made
next part of the activity. A digital camera may
simultaneously from the one set. If only one
be useful to help students record information.
K’NEX Real Bridge Building set is available,
SECTION I
two groups of 4-6 students each may be

involved in this activity, while other students
WHOLE CLASS might carry out a research project on the
• Discuss the results of their investigations Golden Gate and other suspension bridge
and what they have learned about suspension designs. On completion of each activity the
bridges. You may want to raise some of the two groups can change roles, with the
following points: Internet group making use of the completed
• Where and in what types of locations are bridge model.
suspension bridges used?
• Why does this bridge design suit these
particular locations? OBJECTIVES
• What are the advantages and disadvantages For students to learn:
of suspension bridges? (For example: the • How the location/site and the intended use
effects of environmental loads.) of the bridge influences its design.
• Compare the advantages and disadvantages • The key features of a suspension bridge
of cantilever and suspension bridge designs. design and how the bridge design takes into
account the forces that act on it.
MATERIALS
this point or may be incorporated into one of • K’NEX Real Bridge Building set(s)
two larger activities such as: • Copies of the Building Instructions: Book 2
(available on the accompanying CD-ROM)
Section II: Case Study of a Bridge Design
• Slotted masses (10g-1000g)
and/or
• Access to the Internet to carry out selective
Section III: Bridge Construction – research on suspension bridges
An Exercise in Teamwork, Planning and
Implementation
78
Skill Builder 8
Teacher’s Notes
THE INVESTIGATION 9. Would the students use their K’NEX

• Students will construct, test and observe what bridge model design to make a full-scale
happens to their structure when it is loaded at construction? Ask them to explain
different points along its length. their reasons.
• It may be useful for students to measure the

load on the bridge by placing each tower on
THE PROCESS a top pan balance and to trace the loading on
WORKING IN GROUPS OF 4-6 each tower as the load moves from one side
• Each group should continue building the of the bridge to the other. This investigation
model of the Golden Gate Bridge from will help demonstrate to the students how the
Step 15. They should remove the parts loading on a bridge is not equally distributed
they used to modify the towers in the - it is greatest on each tower when directly
SECTION I
earlier investigation. over each one, and at a minimum when in the
middle of the span. The maximum loading on
• Suggested investigations for students to the beam, however, will occur at its mid-point.
undertake once the bridge construction
is completed: Notes about the K’NEX model bridge:
1. What are the structural concepts used in • The towers in the K’NEX Golden Gate Bridge
this bridge design and how are they model are in fact held together - Steps 21 and
applied? 30 in the Building Instructions. This does not
happen in real suspension bridges. The role of
2. How did the location of the bridge
these parts is to stabilize the model’s structure
influence its design?
when under load. Students could be asked to
3. How does their K’NEX bridge model comment on how the towers are stabilized in
behave when loaded in different positions? reality. What stops their bases from moving?
(Remove the components added in Steps
21 on Page 43 and Step 30 on Page 46 • When loaded at the mid-point of the central
of the Building Instructions when testing span, the two towers will bend as in the
the bridge). original investigation. What would they have
4. What happens to the towers when the to do to counteract this effect in their model?
bridge is loaded at its central point once How is this solved in the real bridge design?
the supporting structures are removed Refer students to:
(Steps 21 and 30)? http://www.brantacan.co.uk/
bridgedefs.htm#Susp for a diagram of a
5. What forces are acting on the bridge when
suspension bridge anchorage design.
it is under load and how do they affect it?
6. Do parts of the model move? How are • As part of their record keeping, students
these potentially disastrous problems could be asked to make scale drawings of
solved in the real bridge structure? their K’NEX Real Bridge using measurements
7. What is the maximum load the bridge can taken directly from their model.
support on its main span? Note where and
how any failure occurs. • Each member of the team should write a
report on the Golden Gate Bridge design.
8. If their suspension bridge is anchored It should include their practical investigations
more effectively will its load bearing ability and how the behavior of their bridge model
be affected? compares with that of the real bridge.

79
Skill Builder 8
Teacher’s Notes
INTERNET RESEARCH teacher’s guide, a transcript of the TV program,

Students should be asked to carry out animations, facts about the people and events
research on at least two different named involved in the bridge and a section incorporating
suspension bridges. They could be provided ‘bridge math.’
with the links cited below to obtain additional
facts, statistics and photographs for inclusion http://www.clifton-suspension-bridge.org.uk/
in their reports. Information on the historic Clifton Suspension
Bridge, Bristol, UK.
Some possible areas of research:
• The design challenges caused by the http://www.design-technology.org/
physical conditions of the site and how they suspensionbridges.htm
were solved. A good source of general information, with links
to other web pages on bridges and aspects of
SECTION I
• The environmental forces that act on design and technology.

suspension bridges and how these were
taken into consideration in the construction http://www.inventionfactory.com/history/RHA
of the selected bridge. bridg/sbtd/
• What happened when one design went Suspension bridge technical data. A very good
wrong? (The Tacoma Narrows Bridge site full of detailed background information,
disaster.) terminology and drawings to explain suspension
• The challenges faced by the bridge bridge design.
construction crew when making the bridge.
How did they arrange for the cables to go http://www.bardaglea.org.uk/bridges/
from tower to tower? bridge-types/bridge-types-suspension.html
A general bridge site. Highly visual with little text.
• Why are the main spans in real suspension Examples are from the UK.
bridges arched and why do they include
truss construction?
• What alternative designs were considered for
the location and why were they rejected?
• In their opinion, are their selected bridges
successful structures? Why or why not?
The following general Internet web sites are

useful for student research and photographs.
www.howstuffworks.co
www.brantacan.co.uk
http://www.pbs.org/wgbh/nova/bridge/
meetsusp.html
Some additional information on suspension

bridges:
http://www.pbs.org/wgbh/amex/goldengate/
This site chronicles the construction of the
Golden Gate Bridge, San Francisco, USA. It is
the accompanying web site to a public television
program on the same topic and includes a
80
Skill Builder 1
Student Inquiry Sheet
Building a Bridge Can’t Be

All That Difficult, Can It?
CONSIDER THIS • This bridge does not have to support
a load.
A bridge is a structure used to cross
some form of barrier, making it easier to
get from one place to another without having
• The bridge does not have to be a
freestanding structure but can simply
to make long detours. span the gap between two desks or
• What are the key features you think a two chairs.
bridge should have? Make a short list in
SECTION I
• Your team may use a maximum of 15
your workbook or journal. Rods and 15 Connectors for the bridge.
• What should a bridge not do when you • You have 20 minutes for thinking,
travel across it? Keep these features in building and recording.
mind when you make your own bridges. • Measurements required:
1. The maximum gap your
In this activity your team is challenged to bridge spans.
make 3 simple beam bridges from K’NEX 2. The maximum gap your bridge
materials and then investigate how they spans without sagging or bending.
behave when forces are applied to them.
Think of a beam as a heavy board supported
at either end and used to span a gap.
WHAT TO DO?
1. Once your team has selected the Rods
and Connectors, spend a few minutes
MATERIALS discussing how you are going to tackle
• 15 K’NEX Rods of any length from the the task before starting to build. Some
Real Bridge Building set planning before taking action usually
• 15 K’NEX Connectors of any color from helps. You should keep a record of
the Real Bridge Building set what ideas were rejected, or accepted,
• 50g and 100g weights or slotted masses and why.
• Ruler 2. If you are unfamiliar with how K’NEX
Safety Note: Please wear safety glasses components fit together, ask your
as you undertake these investigations. teacher if you may have a look at
Page 2 of the Real Bridge Building
Instructions Booklets.
CHALLENGE I 3. Once you have completed your bridge,
I. What is the longest bridge you can take the required measurements.
make with the materials provided,
that does not break (fail)?

81
Skill Builder 1
YOUR OBSERVATIONS notebooks or journals.

Think about what you have learned about
Use drawings and written notes to record your
beam bridges:
ideas and observations in your notebooks or
journals. You may want to include responses • Do long beams behave the same way as
to the following questions: short beams?
• How does your bridge perform against • How and where did your structures fail?
the expectations you listed at the
beginning of this activity? • Why is it important for your beam bridge
to remain rigid when carrying a load?
• Where does the bridge bend the most?
• Why would you not use your long • What changes might you might make to
bridge design to cross a barrier?
SECTION I
strengthen your design so that the beam

• How might you strengthen (reinforce) will remain rigid over a longer distance,
your bridge so it can carry a 100g load even when a load passes over it?
at its mid-point?
• How do structural engineers solve the
problem of keeping the bridge span
CHALLENGES II AND III structure rigid over long distances?
II. What is the longest bridge you can
build that can span a gap and carry a
100g load at its mid-point? REPORTING BACK
Your team may use a maximum of 15 Using written text and drawings, produce a
Rods and 15 Connectors for the bridge. short report of no more than 100 words on
the strengths and weaknesses of each
III. What is the longest bridge you can of the bridges you made, using the correct
make that will support a 50g load technical vocabulary when describing your
without sagging or bending? observations.
Your team may use a maximum of 15 • What ideas were rejected or accepted
Rods and 15 Connectors for the bridge. and why?
• Maximum time allowed: 15 minutes • How did your bridge perform against
for each challenge. your expectations/the design
specification?
• Measurement required for Challenge II:
The maximum gap your bridge spans. • What changes did you make to the
bridge structure during construction
• Measurement required for Challenge III:
so that it could meet the new design
The maximum gap your bridge spans
specifications?
without sagging or bending.
YOUR OBSERVATIONS VOCABULARY

beam, load, dead load, live load, span,
Use drawings and written notes to record
bending, sagging, rigid, fail, failure, strength,
your ideas and observations in your
design specifications, structure
82
Skill Builder 2
Investigating 2-D Shapes -

Rectangles and Squares
CONSIDER THIS Compression forces are squeezing forces.
M any buildings and structures include

rectangular or square shapes in their
construction but are they the strongest
Tension forces are stretching forces.
shapes available for this purpose? Shear forces work in opposite directions
SECTION I
and in different planes to each other.
• Think about and make a short list of the
advantages and disadvantages of using A less common force is Torsion, which acts
rectangles in structures. to twist a material.
In this activity your team will investigate how

rectangles and squares behave when forces MATERIALS
are applied to them. The diagrams below • A selection of blue, red, yellow and gray
show the most common forces that affect K’NEX Rods
structures:
• A selection of K’NEX Connectors
• A rubber band at least 12.5cms (5”) long
PART 1: What happens

Compression forces
when forces are applied
to the corners of squares
and rectangles?
WHAT TO DO?
1. Using blue, red, yellow and gray Rods
together with your choice of Connectors,
Tension forces make 3 different sized squares and
1 rectangle. The rectangle should be
made using blue and either red or
gray Rods.
2. Investigate what happens to the shapes

of the squares and rectangles when you
Shearing forces apply compression, tension and shear

83
Skill Builder 2
forces to their corners, then answer the • What happens to the joints when the
questions outlined below. forces are applied?
3. To help visualize what is taking place • What happens to the shapes when the
construct another square using 4 yellow forces are removed?
Rods and 4 blue Connectors. Hook the
ends of a rubber band over the prongs • Are rectangles and squares stable shapes?
of the diagonally opposite Connectors.
Use a rubber band that is at least 3/4 the
length of the diagonal of the quadrilateral. KEEPING A RECORD
If you use the arrangement suggested
• Record and explain your observations
above you will need a rubber band that
through notes and drawings in your work
SECTION I
is approximately 12.5cm (5”) long. If you

book or journal.
have attached the stretched rubber band
(under tension) along the line in which
• Use the correct technical vocabulary to
you are applying the force, you should
describe and explain your observations.
be able to see how the band stretches
further, or relaxes, as the structure
• Make use of directional arrows to show
undergoes compression or tension.
compression:
IMPORTANT SAFETY NOTE: If the tension:
structure is squeezed or pulled too hard the
and shear:
joints may snap open ejecting one or more
connecting Rods from the structure. It is
important that you do not exert too much
force on your K’NEX shapes. Just do enough PART 2: Will adding more
to see the effect and feel any resistance rectangles make a structure
offered by the shape you are investigating.
You should wear safety glasses when more stable?
carrying out this activity. DEFINITION: A stable shape is one that is
able to resist its shape (form) being changed
(deformed).
YOUR OBSERVATIONS Spend a few minutes to think about your
• What happens to the shapes when you response to the question. Record your ideas,
apply compression, tension and shear together with your reasons, in your workbook
forces to their corners? or journal. Now test your ideas.
• Are the shapes deformed (changed)?
What new shapes are produced?
WHAT TO DO
• Do all 4 shapes behave in the same way? 1. Make a chain of equal sized rectangles
and triangles and investigate as before.
For example:
84
Skill Builder 2
PART 3: What happens when

the forces are applied to the
structural members
2. Try your own patterns of squares or
that make up the sides?
rectangles and test them. For example: DEFINITION: A structural member is a part
of the structure that may be subjected to
external forces such as compression,
tension and shear.
SECTION I
WHAT TO DO FIRST
1. Make two different sized squares, one
from the blue K’NEX Rods and one from
the gray Rods.
YOUR OBSERVATIONS 2. Investigate what happens to the squares

when you apply lateral forces to the
• Did the new shapes behave as you sides – you will need to gently squeeze
expected them to or did something the square.
else happen?
3. Use your knowledge of the effects
• Do rectangles and squares make of loads on beams (Skill Builder #1)
stable shapes? to predict how the two shapes
will respond?
• Do rectangles and squares make
strong structures? 4. Spend a few minutes to think about
your response to the question. Record
your ideas, together with your reasons,
KEEPING A RECORD in your workbook or journal. Now test
• Record and explain your observations your ideas.
book or journal.


compression:
tension:
and shear:

85
Skill Builder 2
YOUR OBSERVATIONS
through notes and drawings in your work B
book or journal.
• Did the shapes behave as you expected

them to or did something else happen?
YOUR OBSERVATIONS
• Which size of square is the • Did the shapes behave as you expected
stronger structure? them to or did something else happen?
• How do the structural members behave

SECTION I
WHAT TO DO NEXT in A?
Investigate what happens when forces are
applied along the length (axially) of a • How do the structural members behave
structural member. in B?
1. Use the two different sized squares you
used before. • If you were using squares or rectangles to
design and make structures, would you
2. Stand one of your K’NEX squares on the use large or small-sided shapes? Explain
desktop and push down vertically on one the reasons for your decision.
side as shown in A.
KEEPING A RECORD
book or journal.
A
Desktop
You are now applying an external force compression
axially along a K’NEX structural member. tension
What type of external force is being
applied here?
3. Use your fingers to pull along the long

VOCABULARY
axis (axially) of one side of a square, as frame structures, force, compression,
shown in B. What type of external force is tension, shear, axial, axially, lateral,
being applied now? structure, member, structural member,
stable, unstable, deform, stability, joint,
strong, weak
86
Skill Builder 3
Investigating 2-D Shapes - Triangles
CONSIDER THIS Important safety note: If the structure is

squeezed or pulled too hard the joints may
M any structures use triangles in their
construction, but what makes the
triangle such a useful shape?
snap open ejecting one, or more, connecting
Rods from the structure. It is important that
that you do not exert too much force on
your K’NEX shapes. Just exert enough to
In this activity your team will make some
see the effect and feel any resistance
triangles from K’NEX and then investigate
SECTION I
offered by the shape you are investigating.
their structural properties.
When using rubber bands take care they are
not overstretched and only used in the way
What happens, for example, when forces
described by your teacher. You should wear
are applied to their corners and sides?
safety glasses when carrying out this activity.
PART 1: What happens

when external forces are
applied to the corners and
sides of triangles?
A. Vertical applied force
WHAT TO DO FIRST
1. Using different sized Rods and
Connectors from your K’NEX Real Bridge
Building set, make three or four different
sized triangles.
2. Investigate what happens to the shapes

B. Lateral applied force when you apply the external force in the
directions shown in Fig.1.
Fig. 1: External forces acting on triangles
OBSERVATIONS
• What happens to the shapes when you
MATERIALS apply vertical and lateral forces to
• A selection of K’NEX Rods and Connectors your triangles?
• Rubber bands

87
Skill Builder 3
• Are the shapes deformed (changed)? YOUR OBSERVATIONS

What new shapes, if any, are produced? • Does the rubber band become stretched
or shortened when the vertical force
• What happens to the joints when the is applied?
forces are applied?
• What types of forces are acting on (A) the
• What happens to the shapes when the base and (B) the sides of a triangle when
forces are removed? a vertical force is applied?
• What happens to the structural members? • In A, note what happens when you press
down on the apex of the triangle. Feel the
• Does the length of a side affect how a force pushing back against your finger.
SECTION I
triangle resists external forces?

Some background information
• Do all sized triangles behave in the
This “backward” force is the resistance of
same way?
the rubber band to being stretched and is
called the reaction force. All materials,
• Are triangles strong shapes?
K’NEX plastic, steel, wood, concrete…
behave in a similar way when external
forces are applied to them.
WHAT TO DO NEXT
1. Replace the base of your triangle (A) with External forces are called stresses.
a rubber band and apply a vertical force The most important stresses that act on
as shown in Fig. 2. structures and structural members are those
that tend to squeeze (compressive stress)
2. Replace a side (B) of your triangle with a or stretch (tensile stress) them.
rubber band and apply a vertical force as
shown in Fig. 2.
Note: If you use the blue Connectors for the KEEPING A RECORD
corners of your triangles you can hook the • Record your observations through notes
rubber band around the spare prongs of and drawings in your workbook or journal.
the Connectors. The rubber band should
be slightly stretched before you apply the • Use the correct technical vocabulary to
vertical force. describe and explain your observations.

compression:
tension:
A. Forces acting B. Forces acting

and shear:
on base on a side
Fig. 2: External forces acting on triangles
88
Skill Builder 3
PART 2: Will adding more rubber bands, as shown in Fig. 4.

triangles make a frame 4. Press down at the point indicated by
structure stronger? the arrow and observe what happens
Spend a few minutes to think about your to the rubber bands.
response to the question. Record your
responses, together with your reasons, in
your workbook or journal.
WHAT TO DO
SECTION I
1. Make a chain of equal sized triangles
(See Fig. 3) and investigate as before.
NOTE: A framework of triangles, as used in

Fig. 3, is called a truss construction.
The top edge is called the upper chord
The lower edge is called the lower chord

Fig. 4: Replacing the K’NEX structural members
Fig. 3: Chain of triangles
Construction hint: Use blue Connectors to

2. Now test your ideas: join the Rods, then you can hook the ends
• Place one end of your truss construction of the rubber band around the spare prongs
on the edge of the desk while your of the Connector.
partner holds the other end. Either press
down gently, but firmly, on the upper
chord or pull down on the lower chord.
YOUR OBSERVATIONS
• Record your observations through
• What forces are acting on the members
notes and drawings in your workbook
that you are investigating?
or journal.
• Record your observations and
3. Next, try this. Just as you did in Part 1,
explanations through notes and drawings
replace K’NEX structural members with
in your workbook or journal.

89
Skill Builder 3
• Use the correct technical vocabulary to PART 3: Investigating

triangle patterns
compression: WHAT TO DO
tension: Design and test the performance of your
and shear: own patterns of triangles. For example:
DESIGN CHALLENGE
What is the longest linear truss
SECTION I
construction you can make that will not

bend or sag under its own weight or
under a small load?
1. Before you start to build, spend a few
minutes to think about your response to
the challenge. Consider the results you YOUR OBSERVATIONS
obtained from the Skill Builder #1 bridge • Did your triangle shapes behave as
building activity and your investigations you expected them to or did something
in this activity. else happen?
2. Record your estimate, together with your • Make a list of the types of structures in
reasons, in your workbook or journal. which you have seen these shapes used;
what was their function?
3. Now build your truss construction
and test as before. • Why do you think triangles were used in
their design?
4. Did your truss construction behave as
expected? If not, why not? • Record and explain your observations
5. How did the performance of this type of book or journal.
truss bridge structure compare with the
simple beam construction you used in
Skill Builder 1? (Turn your truss onto its
side to make a simple beam bridge
VOCABULARY
construction and compare.) triangle, vertical applied force, lateral applied
force, joint, deform, structural member,
6. Record your observations and reaction, stress, compressive stress, tensile
explanations through notes and drawings stress, compression, tension, shear, upper
in your workbook or journal. chord, lower chord, truss
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Skill Builder 4
Strengthening 2-D Shapes

CONSIDER THIS PART 1: How can square
M any large structures, such as pylons
and cranes, use a combination of
rectangular and triangular shapes in their
and rectangular frame
structures be strengthened
designs. From previous Skill Builder to resist compression,
activities you learned that rectangular
shapes are not as structurally strong as tension and shear forces
SECTION I
triangular structures. to their corners?
In this activity your team will investigate
how triangles can be used to strengthen WHAT TO DO FIRST
rectangular frame structures. 1. Look at Fig. 1 to remind yourselves of
the main types of external forces that
can act on rectangular frame structures.
MATERIALS
• A selection of K’NEX Rods and
Connectors
• Rubber bands Compression forces
• String (approximately 30cm/12in)
• Paper or light card
• Scissors
• Single-hole punch
Tension forces
Important safety note: If the structure
is squeezed or pulled too hard the joints
may snap open ejecting one, or more,
connecting Rods from the structure.
It is important that you do not exert too
much force on your K’NEX shapes. Just
do enough to see the effect and feel any Shear forces
resistance offered by the shape you are
investigating. When using rubber bands
take care they are not overstretched and
use them only in the way described by your
teacher. You should wear safety glasses Fig. 1: External forces that act on rectangular
when carrying out this activity.. frame structures

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Skill Builder 4
2. Make 3 different sized squares and • Which parts of your strengthened frame
1 rectangle. You should use blue, structure are under compression and
red and gray Rods from your K’NEX tension when tested?
Real Bridge Building set, together with
Connectors. The rectangle should be • Explain how each shape has been made
made using blue and red or red and into a strong frame structure? (Remember
gray rods. you can also see the forces at work on
a structural member if you substitute a
3. Before you start your investigation, rubber band for the K’NEX Rod.)
spend a few minutes to think how the
frame structures you have made can Keeping a Record
be strengthened. Record your ideas, • Record and explain your observations
SECTION I
together with your reasons, in your through notes and drawings in your work
workbook or journal. book or journal.
4. Now apply and then test your ideas. • Use the correct technical vocabulary to
Additional K’NEX components will be describe and explain your observations.
needed to strengthen your shapes.
compression:
YOUR OBSERVATIONS
and tension:
• What happens to your strengthened
square and rectangular frame structures
when you apply compression, tension and
shear forces to their corners? PART 2: Does the use of
triangles always produce
• Were you able to reinforce all of the
shapes using K’NEX? Which shape strong, rigid structures?
presented problems?
• Do all the structures behave in the WHAT TO DO

same way? 1. Before you start your investigation,
spend a few minutes to consider this
• What happens to the joints when the question. Record your answer, with an
forces are applied? explanation, in your workbook or journal.
• What happens to the structures when the 2. In Part 1 you discovered that using
forces are removed? triangles in structures (triangulation)
helps make them rigid and strong. Here
• What new shapes are now present in are two frame structures to investigate.
your structures? Structure 1 contains three triangles while
Structure 2 has two triangles – but is one
more rigid and stronger than the other?
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Skill Builder 4
How will they behave when vertical Figure 1. Queen Post Truss
and lateral external forces are applied (i) The base is made from 2 blue Rods
to them? and 1 yellow Rod joined by 2 yellow
Connectors. At each end add a light
gray Connector.
(ii) Each side can be made from 1 yellow
and 1 blue Rod joined by a yellow
1 Connector. Complete the triangle by
adding a gray Connector at the apex.
(iii) The central rectangle can be made using
blue and yellow Rods.
SECTION I
Figure 2. King Post Truss
(iv) Build the base using 2 yellow Rods
joined by 1 yellow Connector and at
2 each end add a light gray Connector.
(v) Construct each side from 2 blue Rods
joined by 1 yellow Connector. Complete
the triangle by adding a gray Connector
Information: Structure 1 is an example of a Queen Post at the apex.
Truss and Structure 2, a King Post Truss.
(vi) The vertical column is a yellow Rod.
5. How would you modify both structures

3. Record these shapes in your workbooks to make them stronger?
or journals. Explain which one you think
is the stronger and more rigid structure
and why.
4. Now build and test the two structures to

check if you are correct. You will need
the following K’NEX pieces from your
Real Bridge Building set:
• 7 yellow Rods
• 10 blue Rods 3
• 7 yellow Connectors
• 4 light gray Connectors
• 2 gray Connectors 6. Here is a third frame structure to
investigate. This is the strongest and
most rigid of the three examples you
have been given. True or false?

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Skill Builder 4
7. Now build and test the structure to

check if you are right. You will need
some additional K’NEX pieces.
YOUR OBSERVATIONS
• Does the use of triangles always produce A. Strut B. Tie
strong rigid structures?
A weak rectangular structure can be strengthened
• Compare your findings with your original using a diagonal brace. A diagonal brace is called a
answer. strut when used to resist compression and a tie when
SECTION I
resisting tension.
KEEPING A RECORD WHAT TO DO

• Record and explain your observations 1. Build a K’NEX square or rectangle as
through notes and drawings in your work before and test its ability to resist
book or journal. external forces as shown in the
drawings above.
describe and explain your observations. 2. Now replace the K’NEX diagonal
member using string and test again.
• Make use of directional arrows to show Note: There is no need to tie knots at
compression: each corner. Simply wrap the string
and tension: around the Connector prongs a
few times.
3. Before you start to test the structure,

PART 3: Materials such as record the shapes labeled C, D, and E
steel cables, rope and string (shown below,) in your workbooks or
journals and predict how you think the
are only strong when under shape of the frame structure may or may
tension. How can materials not be deformed (changed).
such as these be used to 4. Now test your predictions.
strengthen frame and other
structures?
In this activity you will investigate how a YOUR OBSERVATIONS
material (string), that is strong only under • Observe and record what happens to the
tension, can be used to strengthen weak square and string as you apply external
frame structures. forces as shown in C, D and E below.
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Skill Builder 4
• What forces are acting on the structure YOUR OBSERVATIONS

and string? • Observe what happens to the paper strip
when forces are applied to the structure.
• A similar exercise could be carried out

with a sheet of paper cut to the same size
as the K’NEX flexible square. In this case
the paper is acting as a tension member.
C D
SECTION I
G
Once the paper sheet is in place it acts in

the same way as the diagonal members in
A and B. This method of strengthening a
frame structure is called a diaphragm and
E
is often used to make rigid walls or floor
panels in frame buildings.
WHAT TO DO NEXT
1. Place the square structure on a flat
KEEPING A RECORD
surface and insert a small gray Rod • Record and explain your observations
vertically into the hole in each of the through notes and drawings in your work
corner Connectors. book or journal.
• Use the correct technical vocabulary.
2. Punch holes at each end of a strip of • Make use of directional arrows to show
paper or thin card and fit the holes in
the paper over two of the white Rods, compression:
as shown below. and tension:
3. Now repeat the activity in which you

apply external force to the structure. VOCABULARY
triangulation, diagonal brace, strut, tie,
compression, tension, members, stable,
unstable, stabilize, strong, rigid, stress,
F queen post truss, king post truss,
diagonal, diaphragm

95
Skill Builder 5
Making 3-D Frame Structures - Cubes
5A: INVESTIGATING A CUBE

STRUCTURE
CONSIDER THIS
I n earlier activities you investigated the
effect of external forces on 2-D shapes
and structures and explored how
SECTION I
triangulation can be used to strengthen Fig. 1: Isometric drawing of a cube

frame structures. In this activity you will
use this knowledge to make and strengthen
3-D frame structures. To construct your cube you can use
EITHER:
• Blue Rods and a combination of blue and
gray Connectors (see Page 2 of the
Materials Building Instructions for how to join these
• A selection of K’NEX Rods and Connectors). This will build a small cube.
Connectors OR:
• Building Instructions Booklet: Page 2 • Red Rods and all gray Connectors. This
• Weights (books or 500-1000g masses) will build a larger cube.
1. Estimate how many Rods and Connectors

Safety Note: Please wear safety glasses as you will need to make your cube.
you undertake these investigations.
2. Build either the blue cube or the red cube.
3. Now investigate how your cube behaves

PART 1: Investigating the when supporting a large load. The load
effects of external forces (books or masses) will be placed on the
top of your cube. This means that the
on a cube load forces will act vertically on
your structure.
WHAT TO DO FIRST • What other investigations did you
• Fig. 1 is an isometric drawing of the cube carry out that involved vertically
you will make using your K’NEX Real applied forces acting on rectangular
Bridge Building set materials. frame structures?
96
Skill Builder 5
YOUR OBSERVATIONS
• What is the largest load your cube can
support before there are signs that the
structure is failing? (Do not load it so
much that it actually fails.)
Shearing forces
• How and where did the failure occur?
• What type of force acts on the vertical

structural members of your cube?
• Rectangles are weak structures but what
SECTION I
do you notice about the size of load that
a cube can support?
• Compare your results with a group that Compression forces

built a different sized structure. Is one
stronger than the other, based on your
loading of the cubes?
KEEPING A RECORD
• Record your observations and
explanations using notes and drawings
with directional arrows to indicate the
types of forces acting on the structural Tension forces
members. You should use the correct
technical vocabulary in all written and
descriptive text.
WHAT TO DO NEXT Torsion forces

How does your cube behave when
subjected to different types of forces?
Fig. 2: Forces acting on cube faces
• There are four main types of force that
can affect structures: shear; compression;
4. Before starting your investigation,
tension and torsion. See Fig. 2: Forces
spend a few minutes to think about the
acting on cube faces.
question. Record your ideas, together
with your reasons, in your workbook
or journal.
5. Now test your ideas.

97
Skill Builder 5
Important safety note: If the structure is • K’NEX Rods can be used as struts
twisted too much then the joints may snap • String can be used as tension members
open ejecting one or more connecting
Rods from the structure. While this effect Note: Do not cut the string that comes with
demonstrates a dramatic failure of the your K’NEX Real Bridge Building set, as it
structure, you should not exert too much force is needed for other activities. If other lengths
on the structure because of the potential of string are not available you can simply
hazard from the ejected Rods. Make sure wrap the K’NEX string around the open
you are wearing safety glasses. Connector joints.
2. Modify your cube using EITHER the

YOUR OBSERVATIONS gray Rods (for the red cube) OR
SECTION I
• Did your cube behave as you predicted? the yellow Rods (for the blue cube)
If not, why not? and string.
• Why do you think your cube behaved 3. Test your cube by applying the same
in the way it did when subjected to the external forces as you used on the
different forces? un-reinforced structure.
• How might you strengthen your

cube structure? YOUR OBSERVATIONS
• Must triangulation be applied to all faces
of your cube to strengthen it?
PART 2: Strengthening
3-D cube structures • How does triangulation affect the rigidity
of your K’NEX cube?
In earlier investigations you discovered:
• Weak 2-D rectangular structures could be
strengthened using triangulation.
TALK ABOUT
• Triangulation can involve the use of • How do the designs of electricity pylons,
diagonal braces that can act to resist crane jibs and tall radio masts take into
compression (struts) and/or tension (ties). account the forces that act on them?
• A K’NEX cube is an example of a

frame structure. KEEPING A RECORD
• Record your observations and explanations
using notes and drawings with directional
WHAT TO DO arrows to indicate the types of forces
1.In this investigation you will use acting on the structural members.
triangulation (adding struts and ties)
to reinforce and strengthen your
K’NEX cube.
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Skill Builder 5
5B: EXTENDING THE ACTIVITY - WHAT TO DO FIRST

MAKING LONG BEAM BRIDGES 1. Plan how you will construct your beam
bridge. You might want to consider
the following:
CONSIDER THIS a. How can you use your resources
In this activity you will work in a team of 4-6 most effectively?
to construct 2 beam bridges, each with a b. Do you need to draw a flow chart of
span of 70-80cm. You will build your beams the tasks that have to be completed?
from a chain of cubes or rectangles, but one c. How many K’NEX components are
beam will be thicker than the other. needed? (You can use your previous
• Beam A will be made using the white Rod experience of constructing cubes to
SECTION I
as the depth measure. help you estimate.)
• Beam B will be made using the yellow d. Can any parts be pre-assembled?
Rod as the depth measure. e. Does everyone have a specific job
to do?
• Do not use any triangulation in the first
part of the investigation, just build a 2. Collect your parts and construct the
connected chain of cubes or rectangles. two beams. Remember: do not use
triangulation yet.
3. When completed, balance the beams

on sets of piers (books can be used,
Beam A
but make sure both sets are the same
height) and load each beam at its
mid-point. Add weight until the beams
begin to sag. Make a note of this weight.
4. OPTION: You could use two top

loading/top pan balances as the piers.
Beam B
Observe what happens as you move the
load along the beam.
YOUR OBSERVATIONS
• Did Beam A and Beam B behave
Safety Note: Please use safety glasses differently when loaded? If so, in
when undertaking these investigations. what way?
• Where does the load have to be located

on the beam for the piers to experience
the least amount of force?

99
Skill Builder 5
WHAT TO DO NEXT however, are strongest when compression

5. Triangulate your beams: Add struts or tension forces act axially (along
and ties and then repeat the same their length).
investigation.
For this activity you will be working as part
6. Compare the results of the un-reinforced of a team of 4-6 to build and then investigate
beams with the reinforced beams. the design of the Astoria Bridge in Oregon.
7. Compare the results of the reinforced At the end of your investigation you should
Beam A with reinforced Beam B. produce your own report on the bridge
design. This will include the results of your
8. Does triangulation improve the load group investigations.
SECTION I
bearing performance of a beam?

You could also use the Internet to search
for additional, relevant information and if
available, a digital camera to record
KEEPING A RECORD features of your model design and the
• Record the results of your investigations. results of any tests carried out.
You may want present these in the form
of a simple table or graph.
• Include diagrams wherever you think they MATERIALS

may be helpful. • K’NEX Real Bridge Building set
• Building Instructions: Book 2 for the
Astoria Bridge.
5C: APPLYING THE CONCEPT - • Slotted masses (10g-1000g)
INVESTIGATING HOW ENGINEERS • Ruler
HAVE USED TRIANGULATION TO
MAKE REAL BRIDGES WHAT TO DO
1. Before your group starts construction,
CONSIDER THIS take a few minutes to look through the
building instructions for your bridge.
In Skill Builder #5A you investigated how
Then ask yourselves the following:
3-D frame cube structures can be reinforced
• Does every team member understand
using triangulation.
the building instructions?
When designing structures it is important to • How do you, as a team, plan to
know which parts of your structure will be construct it?
under compression and tension. You may • What roles are needed to complete
recall that long beams can bend when they the task?
are subjected to compression and tension
at the same time. Structural members,
100
Skill Builder 5
• How will you organize the supply as might occur in the real bridge in
of materials? high winds? How does the real bridge
• Does everybody need to be involved in design take into account the effects of
construction? Can those not involved torsion due to high winds?
in construction carry out an Internet • What are the structural engineering
search for information that can be used concepts used in the bridge design and
by the rest of the team to compile how were they applied?
their reports? • Why is the road decking of the Astoria
• Make the best use of the team’s Bridge slightly arched?
available time and resources. • Compare the design of your K’NEX
bridge model with the real bridge. Use
SECTION I
2. Now construct your K’NEX Real Bridge photographs obtained from the K’NEX
model in the time allocated by your teacher. Building Instructions booklet or from
approved Internet web sites.
3. Investigate the model bridge’s load
bearing ability, the forces acting on it,
how they affect the bridge and where
you might expect failure to occur. EXTENDING THE INVESTIGATION
Carry out an Internet investigation on the
Astoria Bridge using some of the Internet
links below. These sites provide you with
YOUR OBSERVATIONS some additional facts, statistics and
Your investigations should provide photographs with which to analyze the
responses to the following: design and construction of your bridge.
• What is the maximum load the bridge Some areas you may want to research:
can support at the mid-point of its • The design challenges caused by the
span? Note where and how any failure physical conditions of the site and how
in the structure occurs. they were solved.
• How does your K’NEX bridge model • The types of forces acting on the
behave when loaded in different bridge and how the design takes them
positions? into account.
• What forces are acting on your model • Why this particular type of bridge
when it is under load and how do they design was chosen for this location.
affect it? Do parts of the model move?
How are these potentially disastrous • The challenges facing the bridge
problems solved in the real bridge construction team and how they
structure? were overcome.
• Would you use the K’NEX model • The alternative designs that were
design as the basis for a full-scale considered and why they were rejected.
construction? • In your opinion, is the bridge a
• How does the K’NEX bridge design successful structure? What are your
behave when subjected to torsion, reasons for your opinion?

101
Skill Builder 5
This is a useful web site for the Astoria

Bridge.
http://www.oldoregon.com/visitor-info/
entry/astoria-megler-bridge/
You can obtain additional resources by

entering Astoria Bridge – Oregon in a
search engine.
SECTION I
102
Skill Builder 6
Spanning Gaps - Beams or Arches?
CONSIDER THIS MATERIALS

T he history of bridge building documents
the ways in which engineers have
tackled the problem of crossing wider and
• K’NEX Real Bridge Building set
• Building Instructions for the Chesapeake
Bay Bridge (Book 1)
wider barriers. To cross wide gaps, strong
and rigid structures are needed. • Rulers and pencils
SECTION I
• Slotted or other masses (10g- 1000g)
In earlier activities you investigated the use • Sheets of white paper
of triangulation to strengthen 3-D frame
structures. Here you will investigate an
alternative way of strengthening a simple
beam bridge so that it can extend across PART 1: BEAMS
wider gaps. You will then compare its To investigate the load
characteristics with those of an arch –
a design that has been used in structures
bearing ability of supported
for thousands of years. and unsupported beam
You will compare the load bearing ability
bridges
of each type of bridge by measuring the
amount of sag or bend (deflection is the WHAT TO DO
term normally used) caused by placing
• Work in a team of 4-6. Familiarize
a 500g load at the mid-point of the
yourselves with the building instructions
bridge span.
before you start to build.
You will make your simple beam bridge by
• Half the team will build 2 sections of the
modifying (slightly) the building instructions
Chesapeake Bay Bridge.
for the K’NEX Real Bridge model of the
Suggestion:
Chesapeake Bay Bridge-Tunnel (Book 1).
Build 3 pairs of supporting piers
Your investigations into the arch will use
(Step 1 on Page 5) and 8 lengths of deck
a length of black bridge decking from the
(Step 2, 4 and 6). Join the sections
same set.
together (Step 3, 5 and 7) to form your
bridge. Add the black decking.
On completion of your investigations, you
will write a short report of no more than 200
• The other half of the team will build
words on the two bridge designs, so keep
the equivalent length of bridge but with
notes and drawings of your findings and
piers only at each end. There will be no
observations as you go along.
central supports in this bridge. Add
Safety Note: Please wear safety glasses as black decking.

103
Skill Builder 6
• Each bridge should be placed so that its KEEPING A RECORD

piers are standing on a sheet of paper. • Record your observations using notes,
Draw around the base of the piers so you labeled drawings and directional arrows.
have a record of their original position.
• You could display your measurements
• Now add loads to your bridges and in the form of a data table in which you
observe what happens. Begin with 10g plot load against the measured amount
and continue up to 1000g, if possible. of splaying and/or weight against the
measured amount of beam deflection
• Think about: (bending).
• How you will measure the amount of
bending (deflection) in your beam.
SECTION I
• How you will record your results. PART 2: ARCHES

• How you will present your results to To investigate the load
make them easy to interpret.
bearing ability of an
arch bridge
YOUR OBSERVATIONS
For each bridge:
• What happens to the bridge decking and WHAT TO DO FIRST
to the position of the piers as you load • Work in a team of 2-3. You will need a
your bridge? length of black bridge decking from the
K’NEX Real Bridges set.
• Identify any movement of the piers
by marking their new position on the • Gently bend the piece of decking into an
paper and note the load that the bridge arch shape.
is carrying.
• Are the piers moving outwards (splaying) • Lower your hands to the desktop,
or inwards? still holding the arch in shape. What do
you feel?
• What load is the bridge carrying when
you first see evidence that the beam • Relax your hold on the arch slightly.
is bending? What happens?
• What is the maximum load the bridge can
carry? How great is the deflection of the • How do you maintain the arch shape?
beam when carrying this weight?
Safety Note: DO NOT LOAD YOUR • Take turns doing this.
BRIDGE TO FAILURE.
You should feel both ends of the arch
• Compare your findings for each bridge. pushing against your hands. To keep the
Which bridge was able to carry a load arch shape, you have to push in against
more successfully? How do you explain the arms of the arch as they push out
this observation? against your hands.
104
Skill Builder 6
WHAT TO DO NEXT • How does this compare with the load it

• One team member should hold the arch could carry when it was converted into
in place while another carefully loads the an arch?
mid-point of the arch with a 500g mass. • What types of forces are involved in
Observe what happens to the arch. supporting a beam bridge?
Repeat with larger masses.
KEEPING A RECORD
YOUR OBSERVATIONS • Record and explain your results and
• When loaded with a 500g mass does observations through notes and drawings
the arch show evidence of bending in your workbook or journal.
SECTION I
or sagging?
• What happens to the arms of the arch as • Use the correct technical vocabulary to
the load is increased? describe and explain your observations.
• What must you do to enable the arch to
• If available, use a digital camera to record
keep its shape?
your investigation activities.
• What will happen to the arch if you
remove your hands?
• Can the supported arch carry a 1000g mass? TO COMPLETE YOUR REPORT
• How wide a gap does the arch span when 1.Compare the load bearing abilities of
carrying this weight? beam and arch bridges.
• What type of forces are involved in You may want to include the following:
supporting arch bridges? • The maximum gap each bridge can
span while carrying similar loads.
• What makes the arch a strong structure?
• The forces that act on each bridge
when under load.
COMPARING THE BEAM AND ARCH 2.Where, and in what types of locations,
• Now undertake a similar investigation are beam and arch bridges used?
using the length of decking as a beam. • Why do their bridge designs suit
Carefully straighten it and then rest the particular locations?
ends either on books or on the piers you
• Look at the facts and figures relating
built for the first investigation.
to the Chesapeake Bay Bridge-Tunnel
• Load the beam at its mid-point with a and the Sydney Harbour Bridge in the
500g mass and observe what occurs. K’NEX Real Bridge Building
• How wide a gap can the beam span when Instructions booklets.
carrying this load?
• What is the maximum load that this
beam can support? How wide is the gap
it spans?

105
Skill Builder 7
Investigating Cantilevers
CONSIDER THIS Wouldn’t this suggest that a cantilever

is actually unsuited for use in bridge
T he investigations you have carried out
so far involved simple beams. Beams
are structural members that are subject to
construction? Why might it be used instead
of a simple beam? How can it be made
bending forces. You have seen how a stable so that it doesn’t bend down when
simple beam supported at both ends under a load? Does it need to be balanced
tends to bend in the middle. or supported in some way? In the following
investigations you will explore how the
SECTION I
A cantilever is a beam that is supported at cantilever can be used to build bridges,

one end only. A diving board is an example of as well as a wide range of other structures.
a cantilever. Think about how a spring board
for diving works: with no one on it, the diving Safety Note: Please wear safety glasses as
board is horizontal but as a diver moves to you undertake these investigations.
the free end it bends.
MATERIALS
• Building Instructions Booklet: Book 1
• Slotted 100g masses
• Spring scales
• String
• Rulers
PART 1: Investigating the

effects of forces on a
cantilever beam
WHAT TO DO FIRST
1. You can feel the forces acting on a
cantilever by simply holding the very end
of a length of black decking from the
K’NEX Real Bridge set, or a ruler, in your
fingertips. Holding it firmly with some
pressure applied will make sure that the
106
Skill Builder 7
‘beam’ remains level, but as soon as you 2. Before starting construction, spend a few
release the pressure of your fingers it will minutes familiarizing yourselves with the
start to bend downwards. building instructions and the modification
you have been asked to make.
2. Ask a team member to carefully add a
small weight to the end of the ‘beam’. 3. Build your model and take time to
• What do you notice about the force investigate how it works.
you need to apply to keep the
‘beam’ level?
• What happens if you hold the beam THEN DO THIS
closer to the middle of its length and Investigate the forces that act on a
SECTION I
your partner adds the same weight? cantilever beam.
• Take turns experimenting. 4. You can test the load bearing ability
of your K’NEX cantilever beam in the
3. Now place the ‘beam’ on an upright following way:
book so that most of it is unsupported – a. Place a 100g load at the free end of
as it was when you held the end of it in the beam.
your fingers. Unless you hold it in place, b. Observe the deflection or bend in the
it will probably fall. beam caused by load.
• Add weight to the part of the decking
c. Measure the force needed to raise
that rests on the book.
the beam back to a horizontal position
• Can you balance the beam so that by pulling back on the blue lever
it extends out horizontally without mechanism.
bending downwards?
• Try adding a weight to the free end. 5. Spend a few minutes to plan how you
What do you need to do in order to will carry out the investigation. Refer
keep the ‘beam’ horizontal? to Fig. 1 below. Measurements and
observations to be made include:
This is the principle of the cantilever – it • Length of cantilever beam (L).
can extend unsupported for a considerable • The Deflection at the free end of the
distance so long as the opposite end acts beam (D).
as a counterbalance.
• The Force required to return the main
part of the beam to a horizontal
position (F).
WHAT TO DO NEXT • The effect of the cantilever beam on
1. Refer to the hinged cantilever that the vertical support (S).
can be found in the bridge raising
mechanism of the K’NEX Tower Bridge
model - Book 1, Page 41: Steps 25 – 28.
You will need to modify Step 24 by
replacing the white vertical supports
with longer yellow Rods.

107
Skill Builder 7
Consider • What parts of a cantilever beam are

• How you will measure the amount of under compression and tension?
deflection of the cantilever beam? Compare your findings with a beam that
• How you will record and present is simply supported at both ends.
your results to make them easy
to interpret?
KEEPING A RECORD
6. The starting point for loading the • Complete your investigation by recording
cantilever beam should be as close to your observations and explanations using
the hinge as possible. the correct technical vocabulary.
7. What happens when you load a longer • You should also include drawings of
SECTION I
cantilever beam? Test it and see. You models used in the investigation and
can increase the length of the beam include descriptions of the forces acting
by inserting additional blue Rods and on the main parts of the structure.
yellow Connectors into the bridge beam
at the hinged end.
F
PART 2: Investigating how
L
a long cantilever beam
D can be supported to make
S a stronger structure
Fig. 1
CONSIDER THIS
In earlier Skill Builder activities you used
YOUR OBSERVATIONS triangulation to produce strong structures
• Explain what happens to the cantilever from weak ones.
beam as its length increases. • How might triangulation be used to
support your hinged cantilever beam?
• Explain the effect of lengthening the
cantilever beam on its vertical support? Spend a few minutes discussing this with
How might this affect the cantilever other members of your group and record
bridge design? your ideas and suggestions in your
workbooks or journals.
• What is the longest length of your
cantilever beam (not the vertical support)
that can support a 100g load without WHAT TO DO FIRST
bending? Pushing up from below and/or pulling up
from above can support a cantilever beam.
• Where would you position the load so
that the stresses on the cantilever beam 1. Try making the models outlined below
are maximized?
108
Skill Builder 7
and investigate their load bearing abilities. A string attached to the free end of the
cantilever can be used to pull the cantilever
2. You will need to use an extended up. The string acts as a tension member
cantilever beam for these activities. or tie.
Add blue Rods and yellow Connectors • How is a triangle formed in this model?
(described on previous page) to extend
the length of the beam. • What types of forces are acting
on the tie?
YOUR OBSERVATIONS
SECTION I
• Was either option helpful?
• In A, a long cantilever puts bending forces

on the vertical support. How can this
Add red Rod here
be avoided?
A. Pushing up from below
• In B, what sort of structure is needed to
Use a red Rod as a strut. The upper part support the cantilever?
of the Rod can be connected to a yellow
Connector, while the lower end can be • Are the structures A and B balanced?
wedged in the angle at the base. The strut
now forms the third side of a triangle. • Suggest ideas for solving the problems
found in A and B. Record these in your
• What types of forces are acting on workbooks or journals using notes
the strut? and drawings.
• Does adding a strut help increase the

load bearing ability of the cantilever? WHAT TO DO NEXT
Now try your ideas by modifying your bridge
model.
YOUR OBSERVATIONS
• Did your ideas work? If not, why not?
• How did your ideas differ from those in

A and B?
• What other problems did you find and

how did you solve them?
B. Pulling up from above

109
Skill Builder 7
KEEPING A RECORD KEEPING A RECORD

• Record and explain your results and • If available, use a digital camera to record
observations through notes and drawings your investigations.
in your workbook or journal.
• Outline drawings of models should be
included, along with the descriptions
PART 3: Keeping things and reasons for the decisions made by
your team when solving the problems.
in balance Drawings should use correct symbols to
show the types of forces acting on the
main parts of the structure.
WHAT TO DO
SECTION I
1. For this activity you will need to combine

with another group because two PART 4: Investigating How
cantilever models are needed.
Structural Engineers Have
2. Join your models (A) Back-to-Back and Used Cantilevers to Make
(B) Face-to-Face (see diagrams below).
Real Bridges
3. Investigate the load bearing ability of
your new designs.
CONSIDER THIS
In the previous activity you investigated how
cantilevers can be used in bridge design.
YOUR OBSERVATIONS In this activity you will investigate how
• Why are these double cantilever bridge engineers applied these concepts to two
designs stronger than the single spans very different types of bridges: in Scotland
you investigated in Part 2? The Firth of Forth Bridge (catilever) and the
Dames Point Bridge in the USA (cable-stayed).
• What changes would you need to make
in these bridge designs to allow them to
span a wider gap?
A. Back to Back
B. Face to Face
110
Skill Builder 7
• You will be working as part of a larger WHAT TO DO

team to build and investigate what 1. As a team, look through the Building
happens to your test model of EITHER Instructions to see the size of the task
the Firth of Forth Bridge OR the Dames you have been set.
Point Bridge.
2. Decide how your team can construct
• Once you have completed your your bridge in the time available.
investigation of the bridge you built you • You have the resources available –
will swap with another team and repeat 4-6 people. How are you going to
your investigation with the second bridge. make best use of them?
• Look at the building plans – can parts
• At the end of both investigations, you
SECTION I
be sub-assembled separately?
should produce your own report on the
two bridges to include the results of your • Who can do sub-assembly work and
investigations. You should also use the who will do final construction?
Internet to carry out research on both • What roles are needed to complete
bridges so you can add relevant the task?
information to your report.
• Does every one need to be involved
in construction?
• It is important that you keep good notes
of your investigations and observations. • How will you organize the materials
Use labeled drawings and, if possible, needed by those making the bridge?
a digital camera to record and store • Does every one know what they have
information. to do?
3. Make the best use of your planning

MATERIALS time and the resources the team has
available. Projects often fail because
• 1 K’NEX Real Bridge Building set people simply fail to plan.
• Building Instructions (Book 2) for all the
team members. 4. Now build your bridge and investigate its
load bearing ability, the forces acting on
• Assorted slotted masses (10-1000g)
it, and how they affect the bridge. You
• Rulers should also consider where you might
expect failure to occur.
• Top pan balances (optional)
• String
YOUR OBSERVATIONS
Identify:
• The maximum load your bridge can
support at the middle of the central span.
Note where and how any failure in your
bridge structure occurs.

111
Skill Builder 7
A
• How does your K’NEX bridge model
behave when loaded in different positions
– in the middle, at either end, at the
center of each pier or tower?
• Where might you expect failure to take

place? Did your bridge behave
as expected?
• How did the bridge designer eliminate the
• Identify the forces that act on your model effects of bending forces that may cause
when under load and how they affect it? structural failure?
SECTION I
• In your investigation of the Firth of Forth • Do any parts of the structure move? How
Rail Bridge identify the main structural are these potentially disastrous problems
members that are under compression and solved in the real bridge design?
tension. What would happen if members
were removed from A or B? • Would you use your K’NEX design to
make a full-scale construction? Explain
your reasons.
• How are cantilevers used in each of

the designs?
• How did the location/site of your bridge

influence the design? What other factors
may have had an influence on the design
A of your bridge?
• Compare the construction of your K’NEX

bridge model with that of the real bridge.
Use photographs obtained from the
K’NEX Building Instruction booklets or
from approved Internet web sites.
• Photographs of a cantilever bridge
B col lapse, the Koror-Babeldaob Bridge,
may be seen on http://www.ketchum.
org/bridgecollapse.html.
• In your investigation of the Dames Point
Bridge identify the main structural
members that are under compression and
tension. What would happen if members
are removed from A
112
Skill Builder 7
EXTENDING THE INVESTIGATION The following general Internet web sites are
Carry out research on the two bridges useful for research and photographs.
using some of the links below. This type
of research will provide you with some www.howstuffworks.com
additional facts/statistics and photographs www.brantacan.co.uk
with which to analyze each bridge and its http://encyclopedia.thefreedictionary.
construction. Some areas you may want com/Cable-stayed%20bridge
to investigate:
• The design challenges caused by the Firth of Forth Rail Bridge web sites:
physical conditions of the site and how http://www.pbs.org/wgbh/buildingbig/
they were solved. wonder/structure/firth_of_forth.html
Background information and statistics.
SECTION I
• The types of forces acting on the
bridge and how the design takes them http://www.pre-engineering.com/
into account. resources/forth/forthbridge.htm
Photographs of the bridge, including
• Why this particular type of bridge design its construction.
was chosen for this location.
Dames Point Bridge web sites:
• Both bridges are like giant seesaws. How http://www.bridgepros.com/projects/
do the bridge designs take into account DamesPoint/DamesPoint.htm
loads moving across them? Historical and factual information, plus links
to other sites with photographs of the bridge
• The challenges facing the bridge design.
construction team and how they
were solved.
• Why is the main bridge span of the

Dames Point Bridge slightly arched and
not straight? What does the arch add to
the structural strength of the bridge?
• The alternative designs that were

considered and why they were rejected.
• If, in your opinion, the bridge is a

successful structure and your reasons for
this opinion.

113
Skill Builder 8
Investigating Suspension Bridges
CONSIDER THIS MATERIALS

S uspension bridges have been used
for thousands of years. From simple
footbridges still used in many parts of the
• Building Instructions booklet: Book 2
world today to superstructures thousands of • Scissors
meters long, a suspension bridge is in fact • String (this is in addition to the string that
a simple structure. A rope spans a gap and comes with the set)
SECTION I
a beam is suspended from the rope. What • Slotted masses (20g-500g)

could be simpler?
• Spring scale (optional)
In this activity your team (a group of 4-6)
will be investigating the basic concepts
that lie behind the technology of WHAT TO DO FIRST
suspension bridges.
1. You will be making a simple suspension
bridge. The towers of your bridge can
From earlier investigations you know that
be constructed using the building
long beam bridges do not produce rigid
instructions for those of the K’NEX
structures. You can push the beam up
Golden Gate Bridge model (Book 2,
from underneath using a large number of
Page 35-40: Steps 1-14).
columns or piers, as in the Chesapeake
Bay Bridge-Tunnel, or pull up from above,
2. You will also need to construct a beam
as in cable-stayed bridges like the Dames
from K’NEX material that is approximately
Point Bridge. It is not always possible,
120 cm long. For this you can use Rods
however, to apply similar solutions in
of any size. (It is suggested however,
locations such as San Francisco Bay,
that you make your beam no wider than
U.S.A. or the Humber Estuary, U.K., so an
the length of a yellow Rod.)
alternative – the suspension bridge – is
used when dealing with very wide barriers
3. Divide the building project up among the
like these.
team members. For example, one person
could make the parts shown in Steps 1-14
Safety Note: Please wear safety glasses as
while someone else can be assigned
Steps 15-20 and so on.
4. Once the towers are built you will need to

make the following small modification in
order to attach your beam. The person
responsible for Step 8 should probably be
assigned to do this:
114
Skill Builder 8
• Insert a green Rod on either side of Record your observations and explanations
the uppermost yellow Connector. through notes and drawings in your
workbook or journal. Consider how you
• Add another yellow Connector on either
might overcome the problems you observed.
side of the original one.
• You should now have 3 yellow 7. Will a cable-stayed bridge solution work
Connectors in a row, joined by 2 green for a very long beam bridge?
Rods. Try the following:
• The Rods forming the ends of the
beam can then be passed through the • Carefully remove the ends of the beam
holes of the yellow Connectors. You can from the yellow Connectors and then
add some black Clips to hold the Rod balance the beam so it rests on top of
SECTION I
ends in place as you carry out the row of 3 Connectors in each tower.
your experiments.
• Tie string to the mid point of the beam
and either feel the force needed to
return the beam to a horizontal position
or use a spring scale to measure the
force needed.
5. You have now created a simply

supported beam bridge.
WHAT TO DO NEXT
• Look at the position of your hands.
6. Add a small load to the center of the
This will give you an idea of the height
span and observe what happens (a) to
of the towers needed to make a
the beam and (b) to the towers.
cable-stayed bridge.
• Compare the length of the bridge with

the height of your hands (the height of
your cable-stayed bridge tower)
remembering that in reality your bridge

115
Skill Builder 8
may be over 3000 meters long with a YOUR OBSERVATIONS

single span of over 1500 meters. Observe what happens to your simply
supported beam bridge and the towers.
• Is it a practical solution to construct a • Is simply attaching a cable to the tops of
tower this height? Explain the reasons the towers and suspending the beam
for your response. from it the solution?
• What happens?
NOW DO THIS
8. (a) Connect the tops of the two towers • What changes would you make to this
using string (A) from your K’NEX Real bridge design, to make it a more practical
Bridge Building set, but do not cut it, design, capable of supporting both live
SECTION I
as it will be needed for other activities. and dead loads? Include drawings of
your ideas in your report.
(b) Use a separate piece of string (B)
to connect the cross cable with the
beam bridge. This vertical cable is called FINAL STEPS
a hanger. 9. Untie the string (cable) from the towers
and place each end over the top of the
towers (do not tie it to the tops); team
members should hold each end of
A the string. Connect a hanger to the
B bridge span.
10. Team members at each end of the

bridge should pull on the free ends of
the string until the beam bridge
becomes horizontal again.
Load
116
Skill Builder 8
YOUR OBSERVATIONS
Observe what happens to your simply
supported beam bridge and the towers now.
• Is one central hanger enough to support
the beam?
• What might happen to your beam bridge

if a load was placed halfway between
the central hanger and a tower? Try it
and see.
• How would you modify your design to
SECTION I
solve any problems observed?
• What types of forces are acting on (i)

the towers, (ii) the main cable and (iii)
the hangers?
• How are the main cables anchored in real

suspension bridges?
• What do you think might happen to the

Golden Gate Bridge if one of the main
cables broke?
KEEPING A RECORD
• Using the correct technical vocabulary,
record and explain your observations and
findings through notes and drawings in
your workbook or journal. Make use of
directional arrows to show
compression:
and tension:
in your models.

117
Case Study
Case Study of a Bridge Design

THE CASE STUDY SUGGESTED TIME REQUIREMENTS
D esigned as a collaborative activity, groups
of 4-6 students develop their knowledge
and understanding of structures through
2 x 70 minute sessions to allow for planning,
implementation, preparation.
investigations of famous bridges (one per 1 x 35 minute session for group presentations
group) and the factors that influenced their of results.
design and construction.
Each group will be expected to plan their INTRODUCTION

research activities, identify specific tasks and Structures come in all shapes and sizes but
roles, use the Internet for searches within
SECTION II
they share one thing in common - they are

chosen parameters, and make use of desktop designed and built to support loads.
publishing, or other word processing software, These loads may be static or dynamic, or a
to produce individual written reports. The group combination of the two.
will be expected to prepare and present their
findings to the class, making use of appropriate Dynamic loads produce much greater forces
presentation software and multimedia hardware. than static loads and their effects must be
assessed when designing and making
This case study complements Applying the structures, even those whose functional life
Concept – Investigating Real World Structures is intended for supporting static loads.
from Skill Builder Activities: 5B, 6B, 7B, 8B and For example:
the Bridge Construction Project – An Exercise • Electricity pylons not only carry the weight
in Teamwork, Planning and Implementation, of power cables, but additional forces may
in which a project team of 4-6 students plan impact them during storms, when high
and organize their activities to complete the winds and snow increase the loading on
construction of a large-scale bridge model the structure.
within a limited time scale. The case study
would be based on one of the bridges used • Furniture, such as chairs and beds, must
in the bridge construction project. Such a be able to withstand not only the weight of
synergistic approach allows students carrying people sitting on them, but also the shock
out the case study to observe the testing of forces of people sitting down or even
a model of the bridge they are investigating and children playing on them.
to incorporate their observations into
their reports. • Large structures, such as bridges and tall
buildings, are also subject to the effects of
As two different bridges can be constructed high winds, or snow and ice build-up, in
and investigated simultaneously using the addition to all the other loads they have
K’NEX Real Bridge Building set, it is possible to support.
for a whole class to be involved in both
activities at the same time. The failure to fully account for the dynamic
effects of a constant wind led to the famous
collapse and failure of the Tacoma Narrows
Bridge, known as “Galloping Gertie”, in 1940.
118
Case Study
All structures are designed and constructed engineers such as Roebling (Brooklyn Bridge)
according to specific engineering concepts. extended the frontiers of bridge construction
To be successful, a structure must not only be by designing and building structures that
able to withstand compression, tension, bending, stretched for over a mile in length.
torsion and shear, but also environmental forces
due to high winds, snow and ice build-up, water Geography students will benefit from
currents, earthquakes and other seismic events. investigating reasons for the location of
bridge structures, their intended purpose,
Using the design and construction of a bridge the needs they meet, the associated transport
as a case study enables students to learn how infrastructure and their impact on human and
an understanding of the forces acting within a other environments.
structure is essential to its overall success.
Bridges are like any other product – they must Just as the design, manufacture, use and
fulfill a practical need. While products such as disposal of many familiar products have an
DVD players, mobile phones, or clothing fulfill environmental impact, so environmental issues
the personal needs of the individual, bridges must also be taken into consideration when
SECTION II
often fulfill the economic needs of a community bridges are designed and constructed. Modern
and a country. What, for example, was the bridges needs thousands of tons of concrete,
need for The Astoria Bridge in Oregon, USA, steel and miles of access roads. What impact
particularly as it gained the nickname of “the will the extraction of the raw materials and
Bridge to Nowhere” during its construction? their production have on the environment and
Why was there a need for a second river local wildlife habitats?
crossing of the Severn Estuary between Bristol
and South Wales in the UK? Why construct Engineers must consider a wide range of
The Queen Elizabeth Bridge across the River factors when they embark on a new bridge
Thames at Dartford, UK when there is a road design and construction project. These
tunnel under the river, or build a bridge across include considerations about its location and
16 kilometers of the Oresund Sound to link site, what it must carry, the distance it must
Denmark with Sweden, when high-speed ferries span, weather and other environmental
already connect the two countries? conditions, safety considerations, aesthetics,
cost factors and budget and time constraints.
A study of the design of structures encompasses These factors, in turn, may also affect the
subjects outside the requirements of Design choice of materials used to construct a bridge.
and Technology. Students studying the The combination of these factors makes the
history of the 19th Century will read about the design and construction process
impact of the Industrial Revolution on human a challenging enterprise.
development. In the USA and in Victorian
Britain, engineers developed innovative design The demands for longer and longer bridges
solutions to make larger and larger structures also required the implementation of new
as new products and technologies became construction methods and the use of new
available. In Britain, engineer-entrepreneurs materials to keep the important balance
such as Derby, Brunel and Telford designed between the weight of the bridge and its
and made giant structures from wrought iron. structural strength and stiffness. Not all
Innovative structures such as the Menai were successful. Learning from catastrophic
Suspension Bridge, the Clifton Suspension bridge failures such as the Quebec Bridge in
Bridge, railroads, and large ocean going ships Canada (collapsed in 1907 and 1916) helped
made from iron, such as the Great Eastern, are modern structural engineers develop improved
examples of their work. In the USA, and safer designs.

119
Case Study
CASE STUDY EXAMPLES The Task

The K’NEX Real Bridge Building set provides The team investigates and evaluates the
examples of 7 famous bridge designs, some design of one of the bridges in the K’NEX
of which demanded innovative engineering Real Bridge Building set. Alternatively, students
solutions to solve the problems caused by might select a bridge within or close to the area
the location and the need to safely span longer in which the school is located.
and longer barriers. Included in the set are the
following categories of bridge: At the end of the investigation each member
of the group should prepare a written report
• Chesapeake Bay Bridge (USA) and/or contribute to a group multimedia
Extended Beam Bridge presentation describing the key features of their
chosen bridge design.
• Sydney Harbour Bridge (Australia)
Arch Bridge As part of this activity students should identify:
• The structural concepts used in the bridge
SECTION II
• Dames Point Bridge (USA) design and how they were applied.
Concrete Cable-stayed Bridge
• The types of forces acting on the bridge and
• Tower Bridge (U.K.) how the design accommodated them.
Moveable Bascule; Suspension Bridge
• The materials used in the construction and
• Firth of Forth Rail Bridge (U.K.) why they were used in preference to other
Cantilever Bridge available materials.
• Astoria Bridge (USA) • The properties that made these materials

Truss; Cantilever Bridge suitable for use in the bridge design.
• Golden Gate Bridge (USA) • Why it was built on its present site.
Suspension Bridge
• Why the particular type of bridge design was
chosen for this site.
OBJECTIVES
Students will learn to: • The challenges facing the engineers when
creating the design for the bridge and how
• Work as part of a team.
they were solved.
• Use the Internet for searches with specific
parameters. • The alternative designs that were considered
• Evaluate information. and why were they rejected.
• Develop oral, written and graphic • How the bridge was constructed, the
presentation skills. problems encountered and how the
engineers solved them. How the construction
engineers prevented it from collapsing before
it was completed.
• The need for the bridge and whom it serves.
120
Case Study
• How the building of the bridge impacted the USEFUL INTERNET WEB SITES
local environment. For example: http://www.matsuo-bridge.co.jp/english/
• Were the local communities impacted by bridges/index.shtm
increased or reduced traffic/quality of life This site gives offers background information,
issues; what effects did its construction facts and statistics about different bridge
have on businesses in the area? designs.
• What was the impact of the construction
of the bridge and new access roads on
resources.html
local habitats and wildlife? Did air and
noise pollution from vehicles increase? http://www.pbs.org/wgbh/nova/bridge/
gamesans.html
• If, in their opinion, the bridge is a successful These two sites provide an interactive resource
structure. They should be prepared to justify for students to test their understanding of
their answer. bridges by determining the best bridge design
for a particular location. Both sites are linked.
SECTION II
http://pbs.org/wgbh/amex/goldengate/
THE PRESENTATION A companion site to the PBS television
Students would be expected to use a range of program on the construction of the Golden
Information Technology skills, resources and Gate Bridge. A script of the TV program is
software in the preparation and presentation of available, together with a wide range of other
their research. teaching resources, including facts about the
construction, bridge math, 1930’s engineering
In taking part in this task students would be techniques, people involved in the construction
expected to: and a section on how to use the site in a
• Work as part of a team. multidisciplinary classroom (civics, geography,
history and economics.)
• Use the Internet for searches with
specific parameters. www.brantacan.co.uk
An excellent resource site that addresses
• Use word processing, desktop publishing or every type of bridge. Some of the information
other presentation software to prepare their can be very detailed and technical, but if you
report/ make their presentation. have a question about bridges you will probably
find an answer here. An excellent selection of
photographs.
CONCLUSION
Once every group has presented their findings, www.howstuffworks.com/bridge
engage the whole class in a discussion about A good introductory site for information on the
the advantages and disadvantages of each main bridge types.
type of bridge. As a concluding activity you
may want to have the students assess their http://www.ketchum.org/bridgecollapse.html
knowledge by playing the 'Build a Bridge' Contains references to a number of bridge
game found on the PBS Nova web site collapses, video footage of the Tacoma Narrows
referenced below. Bridge collapse and graphics of the Tay Railway
Bridge disaster.

121
Construction Project
A Bridge Construction Project

An Exercise in Teamwork, Planning and Implementation
INTRODUCTION THE BRIDGE CONSTRUCTION

I n the Bridge Construction Project a team
of 4-6 students must plan and organize their
activities to complete the construction of a
ASSIGNMENT
The task for the project team is to devise and
implement a plan to complete the construction
large-scale bridge model within a limited amount
of a bridge within a strict time limit. Maximum
of time. They will effectively role-play the job of
time allowed for the actual construction phase
construction engineers, who must transfer 2-D
= 45 minutes. Effective planning is essential.
designs into 3-D reality.
Many activities conform to the 80:20 rule which
SECTION III
states that 80% of the effort is spent in the

Two bridges can be constructed simultaneously
planning and 20% in the execution.
from one Real Bridge Building set, enabling
8-12 students to be involved in this activity
This activity is intended to help students
at any one time. On completion of their bridge
develop important life skills through a project
construction, the project team will be expected
that encourages them to:
to make a presentation to the class, reviewing
• Analyze a problem.
their plan, how it worked, and the lessons
learned. • Identify the key elements of the problem
and the order in which they must be done.
By including a presentation element the • Evaluate the resources available.
student teams will need to identify those
• Plan the most effective use of their
parts of the project that are sequential and de-
resources and the time available in order
pendant on each other and other parts, such as
to successfully complete the task they
the presentation, that can run in parallel to the
have been set.
main construction project. Resources can
be allocated accordingly.
At the end of the activity, students are
encouraged to evaluate their own and the
This activity also complements Applying the
team’s performance and to learn from
Concept – Investigating Real World Structures
their experiences.
from Skill Builder Activities 5B, 6B, 7B, 8B, as
well as Section II: Case Study of a Bridge Design
If they have not done so before, students
– a collaborative investigation for 4-6 students,
should be encouraged to investigate the load
in which the group develops their knowledge
bearing ability of their bridge. Additional time
and understanding of structures through an
can be provided for this after the 45 minute
investigation of the design of a famous bridge
construction deadline.
and the factors that influenced its design and
construction. If run together, additional time
For example, you may want to ask your
may be needed for presentations and class
students to investigate and find answers to
discussion.
the following:
122
Investigate and identify: to cover aspects of project planning including

• The maximum load your bridge can the use of flow diagrams and Gantt Charts
support at the middle of the central span. to plan, manage and monitor progress.
Note where and how any failure in your The use of a digital or video camera can also
bridge structure occurs. assist students record progress and information
that may be later used in presentations or when
• How your K’NEX bridge model behaves using desktop publishing software to write
when loaded in different positions – reports.
middle, at either end, at the center
of each pier or tower.
• Where you might expect failure to

OBJECTIVES
take place. Did your bridge behave For students to learn:
as expected? • Planning and team building skills.
• Project management skills.
• Identify the forces that act on your model
SECTION III
when under load and how they affect it. • Problem solving skills.
THE BRIDGES SUGGESTED TIME REQUIREMENTS

The K’NEX Real Bridge Building set provides Maximum 5 x 35 minutes lesson periods to
models of real bridges that require from 260 to allow for planning, implementation, preparation
1000 parts to make. and presentation of results.
For example:
Book 1: • Session 1: 70 minutes: Planning, preparation
Chesapeake Bay Bridge – 267 parts of plans, identification and allocation of roles.
Sydney Harbour Bridge – 673 parts
Dames Point Bridge – 515 parts • Session 2: 70 minutes:
Tower Bridge – 790 parts 5 minutes: Final preparations and organize
resources.
Book 2: 45 minutes: Construction time.
Firth of Forth Rail Bridge – 500 parts 15 minutes: Testing and recording .
Astoria Bridge – 747 parts 5 minutes: Contingencies.
Golden Gate Bridge – 1051 parts
• Session 3: 35 minutes
Building times for individual bridges vary but it Group presentations.
could take one person, working alone, 3 or more
hours to complete. To accomplish the task of Activities might include:
building one of the bridges in a 45 minute target Session 1 (70 minutes):
time, students will need to use team work, and Planning and Preparation
their analytical, planning and organizational skills.
• Analysis of K’NEX Real Bridge Building
With good planning and working effectively plans to formulate a construction plan.
as a team, a group of 4 - 6 students should For example: The K’NEX building plans are
be able to reduce the actual construction time sequential but is one step dependant upon
needed to build their bridge. To help them, another? Are there sections of the bridge
some preparatory lesson time may be needed that can be built simultaneously?

123
• Student teams should: 15 minutes:

• Identify sections of the bridge that can be Testing their bridge design: See: Skill Builder
made as sub-assemblies. Activities 6B, 7B and 8B: Applying the Concept
• Identify tasks for team members; match – Investigating Real World Structures.
their skills to the tasks to be performed
and the order in which the tasks must be 5 minutes:
done. Teams could ask themselves: Who Contingencies – possible time for finalizing
is good at construction? Who has the best presentation details.
IT skills? Who has the best time keeping
and organizational skills? Session 3 (35 minutes):
• Group presentations. Maximum time allowed
• Identify who is to be responsible for the for each presentation – 7 minutes.
overall management of the project and to
see that the project is kept on schedule. • Feedback and class discussion.
• Investigate the logistics of supplying
SECTION III
construction workers with the correct

components when needed; make lists of IMPROVING LEARNING
the K’NEX components needed for each
stage in preparation for the actual PERFORMANCE
construction of the bridge in the Students should reflect on their performances
following lesson. both as individuals and as teams. They should
evaluate their plan, how well it worked,
• Use flow diagrams or Gantt Charts to aid
problems encountered and solutions arrived at,
planning. (The use of Gantt Charts may not
how decisions were made and what lessons
be suitable for younger aged students).
were learned.
Two sets of Real Bridges Building Instructions
• How well did they plan for this activity?
are available but additional photocopies of
What steps did they miss?
specific sub-assemblies may be needed. These
are available on the accompanying CD-ROM
• What problems occurred during the
and should be printed out ahead of time.
construction phase and how did they
An overhead projector or PowerPoint facilities
solve them?
may be required for group presentations.
• How well did they use their resources to
Session 2 (70 minutes):
meet the construction timescale and to
Implement the Construction Plan
prepare a presentation at the same time?
5 minutes:
• How well did they match the skills required
Allow students time prepare the sorting and
for specific tasks with individuals’ skills.
distribution of components from the central
stores – The K’NEX Real Bridges Building Set
• What would they do differently next time?
– ready for their construction teams to use.
45 minutes:
Construction time.
124
Design Project
Working as Design Engineers

The K’NEX Pedestrian Bridge Project
INTRODUCTION of the issues faced by professional engineers.

Depending on the ages, aptitudes and interests
M any students believe that a design and
create assignment ends when they can
demonstrate that their product works. In real
of the students, they can also make use of
spreadsheet software to cost and model their
life, however, the process of getting a product plans, use computer aided design (CAD)
to its target market can often be lengthy. software to produce simple working drawings,
and use planning software to create flow
Professional designers and engineers operate diagrams or make use of Gantt planning charts.
This activity builds upon the skills acquired by
SECTION IV
in a world in which their designs must not only
work and be aesthetically pleasing, but they students in previous sections.
must sell at the right price, in the right market,
and generate a good profit for all those who
have invested in the development and THE K’NEX PEDESTRIAN
production. For a company to be successful
it must be able to gain repeat sales, often BRIDGE CHALLENGE
from the same customer – their satisfaction is A whole class activity involving project teams,
critical to a company’s profitability. each comprised of approximately 4 - 6 students.
Each team adopts the role of a Design
Moving from a single prototype to full Engineering company.
production is a complex process requiring
much planning. In addition, the manufacturing
process itself must be cost effective if it is to OBJECTIVES
meet the financial requirements of the business The K’NEX Pedestrian Bridge Challenge is
that markets and sells the product. intended to help students learn and develop
a range of key skills as they work on a design
Nowhere is this more important than in the and technology project in which they take a
development of a large structure such as product – a bridge – from the design phase
a bridge or tunnel, especially as there is through to its final construction. Their bridge
sometimes only one chance to get it right. must meet cost and time parameters laid
Mistakes in the construction industry can be down in the product specification.
very expensive to rectify. For example, the
cost of removing the excessive movement in The key skills identified include:
London’s Millennium Bridge across the River • Communication – through the generation
Thames – a pedestrian bridge, first opened and exchange of ideas, with peers and
in 2000 – was $7.5million. Controlling teachers, concerning the design of a bridge
manufacturing or construction costs, therefore, that meets the specifications.
is one essential requirement for any successful
business.
This activity is designed to give students an

opportunity to experience for themselves some

125
Design Project
• Numeracy – through measurement, Second session

estimation and costing of activities and 70 minutes:
materials needed for the construction of a Finalizing bridge design, drawing plans, costing
structure designed by the students. materials and planning construction.
• Planning – to take into account the relative Third session

costs of materials, labor and time when 70 minutes:
deciding how best to use available resources Construction, testing, review and presentation
to successfully complete a design and of company results.
create task.
• Team building – within a large group project, MATERIALS

to generate and discuss their own and other
people’s ideas. To deal with conflicting
views and to agree on the best way to work • Copies of the Design Engineering Guidelines
SECTION IV
together to achieve a common goal. for Students

• Copies of the Suppliers Price List/Order
• Problem solving – not only solving specific Form for each team
design and technology problems, but also to
• Weights or masses (10g-1000g)
be able to deal with and resolve conflicting
needs resulting from the project. • Flip chart paper or large sheets of paper
• Information Technology – in the reviewing

of information, preparation and presentation SCENARIO
of their work, and processes involved in The development of new roads throughout the
completion of a bridge design task. region has identified a need for a number of
pedestrian bridges.
• Improving on learning performance – at
the end of the project students will be The company that can design and successfully
encouraged to evaluate the whole process construct a bridge that meets the
and to identify where and how they might
improve their overall performance. • customer’s design specifications
• at the lowest cost
TIME REQUIRED • and can complete on time,

The project can take place over the equivalent can expect to be rewarded with additional
of one 35 minute and two 70 minute sessions. contracts for similar projects in the future.
Part of an additional lesson may be needed These contracts will provide security for
to complete the review and evaluate the company and its workforce for many
their performance. years ahead.
First session
35 minutes:
Understanding the design specifications and
initial brainstorming session.
126
Design Project
THE RULES CONTRACT AWARD

Each company will receive the same set of This will go to the company whose
design specifications. The design teams within design meets their customer’s specifications
the company must: and requirements and makes the greatest
• Design a structure to meet the specifications. profit margin.
• Complete construction within 30 minutes.

EXTENSION IDEAS
• Prepare a presentation to market/sell their
Students could be asked to build a factor of
design to the customer (maximum of 3
safety into their designs and have their bridges
slides for each presentation and maximum
tested until failure occurs.
5 minutes presentation time). No extension
to the 5 minute time will be allowed.
The activity can be extended to the use of
other materials including balsa wood or other
• The presentation should also include the
suitable woods that require a different set of
SECTION IV
company’s estimate for the total cost of
construction skills, knowledge and understanding
the project to the customer. Designing time
of materials.
is not to be included in the construction
cost estimates.
• Shareholders expect a minimum profit

of 20% of the total construction costs:
i.e. Project cost = construction cost + profit
(20% of construction cost)
BONUS PAYMENTS
Completion of construction ahead of schedule:
$100 per minute.
The total value of bonus payments will be

added to the estimated company profit.
If, however, the structure fails to meet the
design specifications, no bonus payments
will be made and penalties will apply.
PENALTIES
• Overrun of contract: $150 per minute.
• Structure fails to meet the design

specifications: 50% of the value of
the contract.
The total value of the penalties will be

deducted from the company profit on
the contract.

127
Design Project
Design Engineering Student Guidelines

The K’NEX Pedestrian Bridge Project
Sunrise County Public Bid # 78680

Job specifications for a pedestrian bridge
1. The bridge should consist of two towers connected by a pedestrian walkway.
2. A clear area for traffic to pass under the bridge will be a box 14cm high by 60cm wide.
No part of the bridge structure may pass through this clear area.
SECTION IV
Clear area for traffic

60 cm
dimensions. These are
14 cm not the dimensions of
the bridge itself.
3. The minimum width of the pedestrian walkway will be 6.5cm.
4. The completed bridge must be capable of supporting a load of 2 kg placed anywhere

on the pedestrian walkway. (When being tested, the bases of each tower may be
supported because in the real world these would be set in concrete footings which
would stop them moving outwards.)
5. The bridge must remain level when loaded.
6. Foot access to the bridge walkway need not be included in the design at this stage.
SUNRISE COUNTY PEDESTRIAN • customer’s design specifications
BRIDGES PROJECT: • at the lowest cost

• and can complete on time (30 minutes
GUIDELINES FOR COMPANIES construction time)
The development of new roads throughout the
region has identified a need for a number of can expect to be rewarded with additional
pedestrian bridges. contracts for similar projects in the future.
These contracts will provide security for
The company that can design and successfully your company and your workforce for many
construct a bridge that meets the years ahead.
128
Design Project
TIME SCALE WHAT TO DO NEXT

• You have three sessions (the first of 35 4. As a team, decide what type of bridge
minutes and two of 70 minutes) to complete will meet the job specification. Remember
the design, planning and construction of a that the company has only 30 minutes of
pedestrian walkway bridge. construction time.
• Your company design team can use the first 5. Brainstorm ideas:
two sessions to research and develop ideas, • Use a flip chart (if available) or a large
design, cost, and plan how your company piece of paper to write down everyone’s
can construct the footbridge within the time ideas before discussing them one by one.
limitations. In the final session your company
• Every person on the team has a valid
will build and test your bridge design.
contribution to make and every idea
should be evaluated on its merits.
• Remember to check with the job
COST FACTORS specifications to make sure your ideas
SECTION IV
• Your company will be given a supplier’s keep on track.
price list for the K’NEX building materials
that you will need to purchase before 6. Finish the session with an agreed outline
starting construction. bridge design to take forward to the next
planning session.
Organizing your Resources

II: Designing and planning
I: Designing and planning phase (70 minutes)
phase (35 minutes) WHAT TO DO
1. Finalize the decision about the bridge type
WHAT TO DO FIRST you will design.
1. Review the job specification for the
pedestrian footbridge and the rules of 2. Assigned tasks to company members.
the competition.
3. Produce plan drawings (front, side and
2. Make sure that all members of the company top elevations).
understand what has to be accomplished
and the rules of the competition. If unsure 4. Decided how the bridge will be constructed.
ask your teacher to explain.
5. Produce estimates for the K’NEX building
3. Good planning is the key to any successful material costs.
project. During this phase it is up to your
team to look at the resources available – 6. Present the bridge design and cost
human as well as material – and to plan estimates for the project to the customer
how best they can be used to complete (your teacher) before the end of this session.
tasks within the time available. Remember other teams also need to do this,
so book an appointment with your customer
at a time that best suits your company.

129
Design Project
SUGGESTIONS (ii). Any components left over at the end

• Keep your presentation short and to the of construction must be sold back to the
point – your customer is very busy and does supplier at half the original price.
not have much time.
2. Estimating Construction Costs
• Look at the design specifications and see • $300 per minute per person in the
what the customer is really looking for from construction workforce.
your design.
Note: The whole team need not be
• Although the maximum time allowed is 5 involved in the construction of the
minutes; plan for 3 minutes as presentations bridge. Construction costs are high but
often overrun. construction time is short (30 minutes)
and the project cannot be too expensive.
Plan for construction. Can any parts of the

ESTIMATING THE BRIDGE’S TOTAL bridge be sub-assembled before being put into
CONSTRUCTION COSTS the final bridge construction?
SECTION IV
Your company must take the following

into account: • To calculate the labor costs, first estimate
1. Cost of materials. the construction time in minutes. Then
multiply the construction time (in minutes)
2. Construction costs. x labor cost per minute x number of people
3. Company profit. involved in the bridge construction.
1. Estimating Cost of Materials For example:

• K’NEX components as per suppliers price 20 minutes x $300 x 4 people = $24,000
list (make sure you obtain this from
your teacher) 3. Estimating Company Profit
• Shareholders in your company expect
• Plastic decking (track) – sold at $100 per piece. a minimum profit of 20% of the total
construction costs.
• Card stock – sold at $10 per cm.
i.e. Project cost = construction cost + profit
• String – sold at $30 per 30 cm. (20% of construction cost)
An order form for K’NEX building materials If the total construction cost of the bridge
must be completed and the cost estimated by is $100,000.
the end of this session. This order form will be Project cost = $100,000 + $20,000
used to collect the K’NEX components from = $120,000
your supplier (your teacher) at the start of the
next session. Note: The Successful Company
The contract for the project will be awarded
Note: to the company whose design meets its
(i). If you need additional components to customer’s specifications and requirements
complete your bridge after submitting your and makes the greatest profit.
order, then prices are doubled.
130
Design Project
Ideas to help you work through 6. You may find that the total time needed to
complete tasks is greater than the actual
the planning sessions time available in class. You may therefore
1. Make sure you all understand the design need to agree to allocate (delegate) specific
brief. Clarify with the customer - your tasks to members of the team.
teacher - if uncertain.
For example: the whole team may be
2. Brainstorm/discuss/research/test possible involved in designing the bridge but
designs for your bridge. Remember every planning how to construct the bridge in
team member’s ideas should be considered. 30 minutes and the preparation of the
Write all the ideas down on a large piece of company presentation and calculation of
paper first and then discuss them. Always project cost may need to be done at the
keep the job specification in mind. same time. Separate teams can work on
these tasks. Allow a few minutes for the
3. Use your K’NEX Real Bridge Building whole team to be informed about each
components to model and communicate team’s work.
ideas within the team. Can you use, or
modify, the plans for bridges you have
SECTION IV
7. Someone could be given the responsibility
previously constructed for this project? of making sure team tasks are completed
on time or negotiating additional time from
4. Draw up plans for your bridge design. other company members if needed.
Ask yourselves:
a. Can it be built in the time available? 8. Where separate teams are involved in
b. Can components that are needed carrying out different tasks, a member
be identified? of each team should be responsible for
c. Do the plans allow your team to prepare keeping the team to its allotted time.
a cost estimate for the materials?
9. Always allow time for tasks to overrun.
d. Can everyone in the construction team Keep some time free at the end, just
understand the plans and their own role in case it is needed.
in the project?
e. Will the completed structure function 10. When planning how to construct your
as intended? bridge, consider if all, or only some, team
members need to be involved. Remember
f. Are there potential weak areas?
you need to keep construction costs to a
g. Does it meet the measurement minimum but still need to get the job done
specifications? in time – beware of penalty costs!
5. Look at the total time available and the tasks 11. Consider the following:
you need to complete in that time. List the • Who will make the plan drawings?
tasks and set a time to complete each task.
• What roles need to be fulfilled and what
Can different tasks be done at the same
are their responsibilities? For example:
time? Which tasks depend on another being
Project Manager to make sure work
completed first? Sequence the tasks in the
is completed on time and meets
order they need to be done – use a flowchart
specifications; Logistics Manager to
or timeline for this.
make sure all the supplies are in the right
place at the right time; Construction
workers to actually make the bridge.

131
Design Project
• Do team members’ skills match the job

they are required to do?
• Can some team members be involved in
sub-assembly work while a small number
complete the construction?
III: Construction Phase

(70 minutes)
RECOMMENDED TIME ALLOCATION
15 minutes (maximum)
• Final check of design and K’NEX
components list.
• Collect K’NEX components from supplier

SECTION IV
and prepare site for the start of construction.
• You are allowed to have all your K’NEX

components laid out for easy and fast
access to help the bridge construction.
• You are not allowed to pre-assemble any

parts of the bridge before construction starts.
• Once construction has started, pre-assembly

of bridge parts can take place.
• Bridge construction.
• No materials can be left on the building site.

All unused materials must be returned to the
supplier and their value worked out.
• Test bridges.
• Complete profit/loss calculations.
• Review and evaluate performance and

lessons learned from the project.
• Present company results and conclusions

to class.
132
IV. Suppliers Price List
A B C D E
PART COLOR COST/ITEM QUANTITY SUB-TOTAL COST
IDENTIFICATION ORDERED [ column (c) x column (d) ]
Purple $10
Black $10
Light Blue $10
Black $10
Orange $20
Light Gray $20
Green $50
Yellow $50
Blue $70
Gray $40
Green $10
White $20
Blue $40
Yellow $60
Red $80
Gray $90
Light gray $5
Bright blue $5
Black $100
Transparent
White $20
(String - any color) $30 per 30 cm.
Card Stock (Paper - any color) $10 per cm.
NAME: TOTAL COST
Note:
ï Returned items will be bought back at 50% of the original cost.
ï Additional items will be charged at double the original cost.
133
Interdisciplinary Activity
An Interdisciplinary Activity
for Real Bridge Building
INTRODUCTION mathematicians call a parabola. Since the

cable forms a known mathematical shape,
T he purpose of this activity is to provide an
interdisciplinary activity for the Real Bridge
Building Set. It will allow science and mathematics
we can use mathematics to investigate some
of the measurements and characteristics of
teachers, or technology and mathematics the cable and the entire bridge system.
teachers, to work together to enhance students’
understanding of math and science concepts, as NOTE: In reality, a suspension cable hangs in
they relate to suspension bridges. a shape that is termed a catenary rather than
SECTION V
a true parabolic curve. When the suspenders

The materials have an additional benefit in that are in place and the total weight of the bridge
they enable students to see that sometimes is brought to bear on the suspension cable, the
their estimations are grossly incorrect and that curve of the suspension cables approximates
with a little forethought, they can arrive at more the shape of a parabola closely enough for
plausible approximations. This is especially true the purposes of this activity and application
when students make estimates of distances and of the mathematical formulas for a parabola.
heights based on photographs and recall.
The standard formula for a parabola is:
This activity also highlights some of the civil
engineering mathematics that come into
consideration when a suspension bridge
is planned. y = ax2 + bx + c
MATERIALS Where: (adapted with bridge terminology)
• K’NEX model of the Golden Gate Bridge y = height of a point along the parabola
• Rulers and pencils (In the case of bridges, the height of
• Graph paper: 4-5 squares to the inch the tower.)
(8.5” by 11”) a = amplitude of the parabola (The larger
• Pictures of suspension bridges the number, the steeper the sides of
the parabola.)
b = the distance the center of the parabola
BACKGROUND is to the left or right of the “y” axis on
Suspension bridges include a long length of a graph
cable, normally made from steel in the largest c = the distance the center of the parabola is
of suspension bridges and rope or vines in the above or below the “x“ axis on a graph
simplest of suspension bridges. These cables
sag as they extend from one bridge tower x = the distance from the center of the bridge
to the next. The cable sags into a shape that to the center of a tower
134
Thus: ACTIVITY 1
If we draw the deck, towers, and cables of a
suspension bridge to scale on graph paper, the THE PROCESS
best location for the (0,0) point of the graph is at Provide each student with a sheet of graph
a point along the road deck that is just above or paper. Inform students that they are going to
below the center of the parabola formed by the draw a scale model of the Golden Gate Bridge,
sagging cable. using graph paper.
• Instruct students to hold their graph paper in
In that case, the value of “b” becomes (0) since a landscape direction.
the center of the parabola falls on the “y” axis of
the graph. Therefore the expression “bx” can be • Have them draw a line across the page
dropped from our formula since “0” times “x” is five squares above the bottom of the page.
always “0.” This makes our math, graphing, and This line represents the deck of the Golden
analysis much easier. Gate Bridge and for graphing purposes it
represents the “x” axis of their graph.
In the case of the suspension bridge, the
SECTION V
amplitude of the parabola is very low. The • Inform students that they are going to
distance between the towers is many times attempt a scale drawing of the bridge, from
greater than the height of the towers. During one tower to the other.
the course of this investigation, students may
begin to realize that camera angles and other • Ask the students to provide the length of the
factors, that lead them to imagine that the span (distance between the towers) for the
towers of a suspension bridge are extremely Golden Gate Bridge or provide the distance
high in comparison to the distance between the for them (4200 ft.) The activity can be done
towers of the bridge, can be very deceiving. If in meters or feet. Many new mathematics
the students solve the formula for a suspension books include examples in their text for
bridge with a known span, they can determine completing problems in a variety of systems
the height of the towers of that bridge. If the so students realize that concepts hold true
students know the height of the towers of a no matter which measurement system
bridge and the amplitude of the parabola, they they use.
can determine the span of the bridge.
• Student should determine a value that
In this activity, students will do the following: represents the distance from one line on
• Bring their knowledge of parabolas from their graph paper to the next so that they
mathematics class. can draw a scale Golden Gate Bridge that
extends nearly to the edges of their paper.
• Draw their estimation of the shape of a Depending on the number of squares to the
suspension bridge to scale on a graph paper inch, each square could represent 100 or
using a known span for their bridge. 150 feet.
• Determine the accuracy of their estimation by • Instruct students to find the center of the line
examining the extent to which their drawing representing the deck of the bridge. Instruct
is reasonable. students to draw a light, vertical line from
their mark to the top of the page. This line
• Determine the amplitude of several famous represents the “y” axis on their graph.
suspension bridges.
• Determine the height of the towers of several

famous suspension bridges.

135
• Have students find the location of the towers • Using the scale of one square representing
of the bridge. Using their scale, how many 100 or 150 feet, have students call out the
squares must they count to the left and to height above the roadway they have drawn
the right of the lightly drawn “y” axis to mark for the center of the parabola. (Answers will
the location of the towers of the bridge? If generally be in the hundreds of feet. Refer
their scale is 100 feet for each vertical line on back to pictures of the bridge to determine
the graph paper, they will count 21 lines to if these values are realistic.) In most cases,
the left of the centerline and 21 lines to the the bottom of the cable’s parabola is
right of the centerline to place marks that somewhere between 5 and 30 feet from the
identify the location of the towers. If their deck of the bridge.
scale is 150 feet for each vertical line on the
graph paper, they will count 14 vertical lines • After discussing the students’ drawings,
to the left and right of the centerline to place suggest that students draw a second line
their marks for the towers. on their graph paper that they feel is a more
realistic representation of the height of the
towers and the distance to which the cable
SECTION V
• Tell students that they are to estimate the

shape of the parabola that extends between sags above the road deck.
the towers and sags toward the deck. (You
may ask them why they had to place a mark
on the road deck to represent the center of ACTIVITY 2
the span. They should respond that this
represents the point where the cable comes THE PROCESS
closest to the deck of the bridge.) • Review the drawings with the students and
inform them that there is a formula that they
• After the students have drawn their parabolas, can use to find the shape of the parabola for
ask them to draw towers that extend to the any suspension bridge:
height they have chosen for their drawing.
Standard parabola formula for a
• Using their original scale of the distance suspension bridge
between graph lines representing 100 or
150 feet, have the students calculate and
report the heights they have determined for
the towers of the bridge in their drawing.
y = ax2 + c
Generally, students make drawings with tower
heights that are far too high. Some students Where:
will have values extending into the thousands
of feet. Begin a discussion of what they think y = height of the tower
a reasonable value would be for the tower
height and see what information and past a = amplitude of the parabola (The larger
experience they bring to the discussion. In the number, the steeper the sides of
most instances, the students readily admit the parabola.)
that they have guessed too high for c = the distance the center of the parabola is
the towers. above or below the “x“ axis on a graph
x = the distance from the center of the bridge
to the center of a tower
136
• Complete the formula for the Golden Gate different characteristic of the parabola that
Bridge to determine the height of the towers. is formed by the cable on the K’NEX Golden
(A value of 0.000112 has been determined for Gate Bridge.
the amplitude of the parabolic curve of the
Golden Gate Bridge.) • The groups will be able to come up to the
front of the room and measure three of the
y = height of the tower values for their bridge and then be allowed
a = 0.000112 to return to their seats to see if they can
c = 5 feet solve for the missing value.
x = 2100 feet (1/2 the 4200 foot span)
• As the teacher, you will need to monitor
y = .000112 (2100)2 + 5 feet the model as the students make their
y = .000112 (4410000) + 5 feet measurements to ensure they do not
y = 494 + 5 feet measure the value they are trying
y = 499 feet to determine.
SECTION V
• Provide the students with small data sheets
• Ask students to solve the general formula to (shown below,) to assist in this process and
determine the formulas to find: to help students with their data collection.
Help them to use a consistent measurement
“x” – or 1/2 the span of the bridge system across the four groups.
“a” – or the amplitude of the parabola
“c” – or the height above the deck the sag Group # 1
of the parabola reaches y = unknown
a = ______________
Students with appropriate math skills should x = ______________
arrive at the following formulas: c = ______________
Group # 2
y = ______________
a = unknown
X= y-c x = ______________
a c = ______________
Group # 3
y = ______________
a = ______________
y-c x = unknown
a=
x2 c = ______________
Group # 4
y = ______________
c = y - ax2 a = ______________
x = ______________
• Break the class into four or eight groups. c = unknown
• Inform the students that each group is (The students can complete this activity
going to mathematically determine a with their bridge or a model at the front of
the room.)

137
ASSESSMENT EXTENSION ACTIVITIES

This same activity can be repeated for other
MAT ACTIVITY
famous suspension bridges around the world.
• Ask the students to get into groups of four Students can easily find data as to the spans
and to sit around a table. of various suspension bridges on the Internet,
in textbooks, or in other reference materials.
• Provide each group with chart paper or a
sheet of easel paper. A similar activity can be used to study arch
bridges. Since the parabola of an arch bridge
Arrange the paper as shown so that there is is curved downwards rather than upwards, the
a triangle-like shape in front of each student. formula will need to include a negative value to
They should put their name in this space. invert the curve. In the case of the arch bridge,
the students would generally be determining
the height of the arch above the surface of
the water.
SECTION V
• Have each student list in the space what they

have learned from their investigations of the
Golden Gate Bridge and parabolas. They
should provide as much detail as possible.
• When students have been give sufficient time

to respond, ask the group to discuss what
they have written and then to put information
they agree upon in the circular space in the
center of the page.
NOTE: The outside of the page presents

you with an understanding of what individual
students gathered from the instructional session.
The center of the page gives you a sense of
changes to individual thought as a result of
discussions with the student’s work group.
You may wish to assign both an individual and
a group grade to this activity.
138
Glossary
The following is intended as a glossary for the teacher. The age of your students,
their abilities, their prior knowledge, and your curriculum requirements will
determine which of these terms and definitions you introduce into your classroom
activities. They should be used to formalize and clarify the operational definitions
your students develop during their investigations.
BRIDGES:
Bridge: A structure that provides a way across a barrier. Something that connects, supports,
or links one thing to another.
Glossary
Beam: A horizontal structure that is subject to bending.
Arch Bridge: A bridge having a curved structure. The arch design provides strength by exerting
force downwards and sideways against the abutments.
Bascule Bridge: A hinged bridge that acts like a seesaw. Sections can be lifted using weights as
a counterbalance.
Beam Bridge: The simplest type of bridge. It is made from a rigid, straight structure resting on
supports (piers, columns, towers) at either end.
Cable-stayed Bridge: A modern design of bridge in which the deck is supported by cables
directly attached to towers.
Cantilever Bridge: Similar to the beam bridge, this design derives its support from counterbalanced
beams meeting in the middle of the bridge rather than from supports at either end. The two arms of
the beam are called cantilevers.
Suspension Bridge: A type of bridge in which the deck hangs from wires attached to thick cables.
The cables themselves pass over towers and are securely anchored in
concrete anchorages.
Truss Bridge: A type of beam bridge, reinforced by a framework of girders that form triangular
shapes.
LOADS AND FORCES:

Load: The distributions of weights on a structure. (See also Dead Load and Live Load below).
Force: A push or pull. In the case of bridges, force is applied to the bridge in the form of a load.
Stresses: Forces that tend to distort the shape of a structure or a structural member.
For example, compressive stresses tend to shorten a member while tensile stresses tend
to stretch it.
Stress: A measure of the force applied to a material and depends on the surface area over which
the force is being applied. Stress = Force/Area and is measured in N/m2 or pascals (Pa)
Strain: A measure of the change in length of a material caused by stress. Strain is the result of stress.
Strain = Change in length/original length

139
Glossary
Young’s modulus or modulus of elasticity of a material: Compares the amount of strain produced
in a material with the stress that produced it. Young’s modulus (E) = Stress/strain
A strong or stiff material will only have a short change in length (steel), whereas a weaker or more
elastic material (rubber) will produce a large change in length. Steel will have a much higher value for
Young’s modulus than rubber.
Compression: A force that tends to shorten, push or squeeze a structure.
Tension: A force that tends to lengthen or stretch part of a structure.
Torsion: The strain produced when a material is twisted.
Reaction (Reactive force): For every action there is an equal and opposite reaction (Newton’s Third
Law of Motion). If an external force is applied to a structure the internal forces within the structure
push back with equal strength against the external force. When the forces are balanced the structure
Glossary
is said to be stable.
Shear: A force that acts to move a material in a sideways motion.
Strength of a structure: Determined by the magnitude of the external forces needed to make it fail.
Strength of a material: Determined by the amount of stress that is needed to make it fail.
Symmetry: An arrangement that is balanced and equal on opposite sides of a central dividing line.
Buckle: A condition that occurs when structural members bend under compression.
Dead Load: The weight of a bridge’s structure.
Live Load: The weight of traffic using the bridge.
Environmental Loads: Additional loads on a structure caused by wind, currents, rain, snow and
ice build up, earthquakes and other seismic events.
BRIDGE FEATURES:
Abutment: The mass of rock or concrete at either end of an arch bridge that keeps the ends of the
arch securely in place.
Anchorage: Foundations/concrete blocks into which the cables of a suspension bridge are secured.
Beam: A rigid, horizontal component of a bridge.
Brace: A support used to strengthen and stiffen structures.
Cable: A bundle of wires used to support the decking of a suspension bridge or a cable-stayed
bridge.
Caisson: A temporary structure used to keep out water during construction of the piers’ foundations.
Cantilever: A beam that is supported at one end only.
Decking: The surface of the bridge that serves as a walkway, roadway or railway.
140
Glossary
Engineer: A professional who researches and designs bridges and other structures. There are many
types, including civil, structural, and environmental engineers.
Framework: A skeletal arrangement of materials that give form and support to a structure.
Frame structure: Made by joining together a number of parts or members – for example a
K’NEX model.
Girder: A strong, supporting beam.
Handrail or Guardrail: A safety feature added to the sides of the bridge’s deck to prevent people,
animals or vehicles from falling from the bridge.
Keystone: The final wedge-shaped piece placed in the center of an arch that causes the other pieces
to remain in place.
Glossary
Member: A part of a frame structure.
Obstacle: Something that stands in the way or acts as a barrier.
Pier: A vertical support for the middle spans of a bridge – a column, tower or pillar, for example.
Pulley: A wheel used for hoisting or changing the direction of a force.
Ramp: An inclined section connecting the shore/banks/approach route to the deck of the bridge.
Roadway: The area of the bridge along which traffic travels; it rests on the decking.
Span: The section of the bridge between two piers.
Support: An object that holds up a bridge and serves as a foundation.
Suspender: A supporting cable for the deck; it is hung vertically from the main cable of the
suspension bridge. Also known as a Hanger.
Strut: A structural support under compression.
Tie: A structural support under tension.
Tower: A tall, vertical support that carries the main cables of a suspension bridge and
cable-stayed bridge.
Triangulation: The use of triangles to strengthen frame structures.
Truss: A framework of girders, some in tension and some in compression, comprising triangles and
other stable shapes.
Voussoir: A wedge-shaped stone block used in an arch. (French: ‘arch-stone.’)

141
Reading/Resources
Additional Recommended Reading/

Resources for Students
Billington, David P. The Tower And The Bridge. Princeton, NJ: Princeton University Press.
1985. ISBN 069102393X.
Dunn, Andrew. Bridges (Structures). Thomson Learning. 1993. ISBN 1568470282.
Gordon, JE. Structures: Or Why Things Don’t Fall Down. De Capo Press. 2003.
Reading/Resources
ISBN 03068128355.
Harris, David W. The Newspaper Truss. BaHa Enterprises. 2001. ISBN 0967549515
(CD-ROM)
Haslam, Andrew et al. Building (Make It Work! Science). Two–Can Publishers. 2000.
ISBN 1587283514 (Reading age: 9-12 years.)
Johman, Carol A. et al. Bridges: Amazing Structures to Design, Build and Test.
Williamson Publishing. 1999. ISBN 1885593309.
Kaner, Etta. Bridges. Toronto: Kids Can Press, 1995. ISBN 1550741462.
(Reading age: 9-12 years.)
Kaner, Etta. Towers and Tunnels. Toronto: Kids Can Press, 1995. ISBN 1550742183.
(Reading age: 9-12 years.)
Macaulay, David. Building Big. Boston, MA: Houghton Mifflin Company. 2000.
ISBN 0395963311.
Oxlade, Chris. Bridges (Superstructures Series). Austin, TX: Raintree Publishers. 1997.
ISBN 0817243313.
___________. Bridges (Building Amazing Structures Series). Heinemann Library. 2000.

ISBN 1575722755.
Salvadori, Mario. The Art of Construction. Chicago, IL: Chicago Review Press. 1990.
ISBN 1556520808.
Williams, David. Truss Fun. BaHA Enterprises. (2nd edition.) 2004. ISBN 0967549523.
Wilkinson, Philip. Building (Eyewitness Books). London: Dorling Kindersley Publishing Inc.
2000. ISBN 0789466074.
142
Useful Web Sites
http://www.brantacan.co.uk/
A valuable resource site with detailed information on all aspects of bridge design and construction.
It offers an excellent selection of photos and diagrams, which can be used in the classroom.
http://www.icomos.org/studies/bridges.htm
This site provides a library of bridge types from around the world. Heavy on text and very detailed,
it serves as a good reference source.
http://eduspace.free.fr/bridging_europe/index.htm
A useful educational web site with links to other sites. It has informative ideas for lessons
Useful Web Sites

and activities.
www.pbs.org/wgbh/buildingbig/bridge/
This web site offers an excellent interactive section where Forces, Loads, Shapes and Materials can
be investigated.
A companion web site to the US television series, “Super Bridge.” A useful source of information on
bridge building, with interactive sections.
http://www.bbc.co.uk/history/british/victorians/iron_bridge_01.shtml
This site offers animated and interactive sections on building an arch and the construction of the
Iron Bridge at Coalbrookdale, England – the first iron bridge. You may need to download a free VRML
plug-in or QuickTime to view these pages. Directions are provided.
http://pghbridges.com/basics.htm
A useful web site with simple line drawings and basic information on different bridge types.
http://www.bearwoodphysics.com/3schemproject3.3.12.htm
An excellent web site with many drawings and diagrams of different bridge types and the forces
acting on them.

143

KNEX EDUCATION Real Bridge Teachers Guide 78680

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78680

K’NEX Limited Partnership Group Acknowledgements:

A NOTE ABOUT SAFETY:

Introduction 2-3 6. Spanning Gaps: Beams or Arches? 103-105

SECTION I: SKILL BUILDERS SECTION IV:

Student Inquiry Worksheets

Real Bridge Building

Overview As students use this K’NEX set they will

and extensive background information to

Real Bridge Building

Bridge Construction: An Exercise in

What is the function of a bridge?

Real Bridge Building

Fig. 3: Strengthening a beam by making it thicker

As the need arose to carry heavier loads across

technology associated with bridge building

The problem with the bridge shown in Fig. 4

Bridges and Forces 1: The Basics

From Newton’s Third Law of Motion you know

Real Bridge Building

event an engineer might increase the values

• What is the maximum distance that the

• What type of rock will underlie the bridge

• How large a working load is the bridge

Bridges and Forces 2:

Fig. 2: Compression Fig. 3: Tension

Fig. 1: Long beam bending

As the name implies, static loads do not move.

Real Bridge Building

Think about what happens when you stretch

(the reaction, or resistance, of the material). Axis

Fig. 10: A long thin beam showing excessive bending

A useful website to visit to explore these

Short heavily loaded

(a) From bending

Fig. 11: Failure due to shear forces

WHAT THICKNESS OF BEAM WILL

Real Bridge Building

limiting ratio for each type of construction

This web site highlights Pre-Stressed Girder

How a column behaves depends on the strength

Load B: Long, slender columns

C: Intermediate length column

Fig. 14: Column size and the effects of compression

A: Short, wide columns

Real Bridge Building

Stress, Strain, Stiffness

large stresses but which are also flexible and

It is important for structural engineers to know

force. From previous Readers you will know

You might assume that small loads will have

Foundations Change in length

Real Bridge Building

Strain values are often expressed as WHAT DO STRESS-STRAIN

Fig. 3: Graph of stress against strain

extension of the material is directly

Fig. 6: Stress–strain graphs Fig. 7: Young's modulus values for some

The steeper the slope of the stress-strain Material E MN/m2