BRIDGE ENGINEERING

COURSE OUTLINE:
! Bridge Superstructure
!Bridges ➣ Reinforced Concrete Slab Bridge
➣History of Bridges ➣ Reinforced Concrete Deck Girder (RCDG)
➣ The Bridge Structure: ➣ Reinforced Concrete Deck Girder (PCDG)
Superstructure and Substructure ➣ Composite Steel Deck Girder (CSDG)

! Bridge Design Principles

➣ Design Consideration for Planning ! Bridge Substructure
➣ Selection of Bridge Structure ➣ Abutments Piers (for continuous bridges)
➣ Foundations

! Special Topics
➣ Bridge Damages
➣ Bridge Retrofitting
➣ Seismic Design of Bridges
BRIEF HISTORY OF BRIDGE ENGINEERING
• Bogdan O. Kuzmanović (1977) • The first major bridge work using wooden
described stone and wood as the trusses was in the 16th century, when
first bridge building materials. Andrea Palladio built triangular trusses to
construct bridges with spans up to 30 m.
• Stone bridges of the arch type Palladio focused on the three basic
were constructed in Rome and principles of bridge design:
other European countries in the • convenience,
Middle Ages. These arches were • appearance, and
half-circular, with the flat arches • endurance.
beginning to dominate bridge work
during Renaissance period.
HISTORY OF BRIDGE ENGINEERING
• One of the outstanding wooden trusses
was developed by Long in 1839. Refer to
figure below:

• Another notable bridge during this

period was the Cascade Bridge of the
Erie Railroad spanning a valley of 533 m
deep and 91 m wide as shown in next
slide:
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HISTORY OF BRIDGE ENGINEERING
v The transition from wooden to steel bridges did not start until about 1840 but the
first recorded use of iron in bridges was the chain bridge built in 1734 across the
Oder River in Prussia.
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v The first all cast-iron bridge was built in 1779 by
Darby at Coalbrookdale according to a design
prepared by Pritchard (De Mare, 1954).
HISTORY OF BRIDGE ENGINEERING
v In 1866 Culmann explained the principles of cantilever truss
bridges, and one year later the first cantilever bridge was
built (1867) by Heinrich Gerber across the River Main at
Hassfurt, Germany, with a central span of 130 m.
HISTORY OF BRIDGE ENGINEERING
v At about the same time, structural steel was
introduced as a prime material in bridge work,
although its quality was often poor.

v Between 1874 and 1883 three major bridges were

built of structural steel:
• Eads Bridge in Mississippi River St. Louis (1870);
• Brooklyn Bridge in New York (1867); and
• Glasglow Bridge in Missouri (1883)
HISTORY OF BRIDGE ENGINEERING
v Eads Bridge in Mississippi River St. Louis (1870)
HISTORY OF BRIDGE ENGINEERING
v Brooklyn Bridge in New York (1867); and
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v Glasglow Bridge in Missouri (1883)
HISTORY OF BRIDGE ENGINEERING
v Toward the end of the 19th century, Maxwell contributed further
improvements to the analysis of truss bridges, particularly in
graphical solutions.

v Kuzmanovic (1977) mentions two important box girder bridges, the

Conway and Britannia bridges designed by Robert Stephenson.
HISTORY OF BRIDGE ENGINEERING
v The Conway Bridge (1848) consisted of a single span of 125.6 m
made of tubular structures for the railroads across Conway and
Menai Straits.
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v The Britannia Bridge (1856) was a continuous structure with spans
of 70 m, 140 m, 140 m, and 70 m.
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v The Britannia Bridge … after
reconstruction in 1972.
HISTORY OF BRIDGE ENGINEERING
v Emile Clapeyron, who introduced the three moment equation
in 1849, made an analysis of Britannia box girder in 1857 and
determined that the bending stresses were not balanced; the
negative moment stresses at the interior supports are 2.5 to 3
times larger than the stresses at midspans, and therefore this
bridge needed a more efficient distribution of plate
thickness.
THE BRIDGE STRUCTURE
Ø BRIDGE defined
Ø A bridge is a structure that crosses over a river, bay, or other
obstruction, or an open intersection (as in interchanges), permitting the
smooth and safe passage of vehicles, trains, and/or pedestrians.

Ø An elevation view of a typical bridge is shown in the figure in next slide.

THE BRIDGE STRUCTURE
THE BRIDGE STRUCTURE
v A bridge structure is divided into an upper part (the
superstructure), which consists of the wearing surface, the deck,
primary members and the secondary members, and a lower part
(the substructure), which are abutments, piers, bearings, footings,
piles and sheeting.

§ The superstructure provides horizontal spans such as deck

and girders and carries traffic loads directly.

§ The substructure supports the horizontal spans, elevating

above the ground surface.
BRIDGE COMPONENTS: SUPERSTRUCTURES
v Superstructure. The superstructure comprises all the components of a
bridge above the supports. The basic superstructure components consist
of the following:
q Deck. The deck is the physical
extension of the roadway across
the obstruction to be bridged. The
main function of the deck is to
distribute loads along the bridge
cross section or transversely. The
deck either rests on or is integrated
with a frame or other structural
system designated to distribute
loads along the length of the bridge
or longitudinally
BRIDGE COMPONENTS: SUPERSTRUCTURES
q Wearing Surface. The wearing surface (course) is that portion of the
deck cross section which resists traffic wear. In most instances this is a
separate layer made of bituminous material. The wearing course usually
varies in thickness from 50 mm to 100 mm; however, this thickness can
sometimes be larger due to resurfacing of the overpass roadway, which
occurs throughout the life cycle of a bridge.
BRIDGE COMPONENTS: SUPERSTRUCTURES
q Primary Members. Primary
members distribute loads
longitudinally and are
usually designed principally
to resist flexure. Beam type
primary members are also
called stringers or girders.
These stringers could be
steel plate girders (i.e., steel
plates welded together to
form an Isection),
prestressed concrete
girders, reinforced concrete
girders, or glued laminated
timber stringers.
BRIDGE COMPONENTS: SUPERSTRUCTURES
Rather than have the slab rest directly on the primary member, a small fillet
or haunch can be placed between the deck slab and the top flange of the
stringer. Some bridge superstructure can be formed in the shape of a box
(either rectangular or trapezoidal). Box girder bridges can be constructed
out of steel or prestressed concrete and are used in situations where large
span lengths are required.
BRIDGE COMPONENTS: SUPERSTRUCTURES
q Secondary Members. Secondary members are bracing between primary
members designed to resist cross-sectional deformation of the
superstructure frame and help distribute part of the vertical load
between stringers.
BRIDGE COMPONENTS: SUPERSTRUCTURES
In most instances, these secondary members are known as diaphragms.
They can be composed of crossed frames at the top or bottom flange of a
stringer used to resist lateral deformation. This type of secondary member
is called lateral bracing.
BRIDGE COMPONENTS: SUBSTRUCTURES
v Substructure. The substructure consists of all elements required to
support the superstructure and overpass roadway. The basic
substructure components consist of the following:

q Abutments. Abutments are earth-retaining structures which support

the superstructure and overpass roadway at the beginning and end
of a bridge. Like a retaining wall, the abutments resist the
longitudinal forces of the earth underneath the overpass roadway
BRIDGE COMPONENTS: SUBSTRUCTURES
v Pedestals. A pedestal is a short column on an abutment or pier which
directly supports a superstructure primary member.

The term bridge seat is also used to refer to the elevation at the top
surface of the pedestal.
BRIDGE COMPONENTS: SUBSTRUCTURES
v Backwall. A backwall, sometimes called the stem, is the primary
component of the abutment acting as a retaining structure at each
approach.
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v Wingwall. A wingwall is a sidewall to the abutment backwall or stem
designed to assist in confining earth behind the abutment.
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q Piers. Piers are structures which support the superstructure at
intermediate points between the end supports (abutments). Piers,
like abutments, come is a variety of shapes and sizes which depend
on the specific application.

From an aesthetic standpoint, piers are one of the most visible

components of a highway bridge and can make the difference
between a visually pleasing structure and an unattractive one. Some
of the basic types of piers which are popular in highways bridges are
hammerhead, solid wall or gravity, column bent and pile bent.
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v Bearings. Bearings are mechanical systems which transmit the vertical
loads of the superstructure to the substructure. Example of bearings are
mechanical systems made of steel rollers acting on large steel plates or
rectangular pads made of neoprene.

The use and functionality of

bearings vary greatly depending on
the size and configuration of the
bridge. Bearings allowing both
rotation and longitudinal
translation are called expansion
bearings, and those which allow
rotation only are called fixed
bearings.
BRIDGE COMPONENTS: SUBSTRUCTURES
v Footing. As bearings transfer the superstructure loads to the
substructure, so in turn do the abutment and pier footings transfer loads
from the substructure to the subsoil.

A footing under a wall is known as a continuous or wall footing; whereas,

a footing under a pier is known as a spread footing.
BRIDGE COMPONENTS: SUBSTRUCTURES
v Piles. When the soil under a footing cannot provide adequate
support for the substructure, in terms of
§ bearing capacity,
§ overall stability, or
§ settlement,

support is obtained through the use of piles, which extend down

from the footing to the proper depth. Some types of pile range from
concrete, either cast-in-place or bored pile, to steel H-sections driven
to sound rock.
BRIDGE COMPONENTS: SUBSTRUCTURES
Some common types of foundations include:
v Spread or isolated footing,
v Driven piles foundation, and
v Drilled shaft or bored piles
BRIDGE COMPONENTS: SUBSTRUCTURES
Steel sheet piles are one of the most common forms of sheeting in use and
can even be used as abutments for smaller structures.
BRIDGE COMPONENTS: SUBSTRUCTURES
BRIDGE COMPONENTS: APPURTENANCES AND
SITE-RELATED STRUCTURES
v Appurtenances. An appurtenance bridge or bridge site which is not
a major structural component yet serves some purpose in the
overall functionality of the structure.

The bridge site, as an entity, possesses many different components

which, in one way or another, integrate with the structure proper.

The major appurtenances and site-related features are as follows:

• Embankment and Slope Protection. The slope that tapers from the
abutment to the underpass (embankment) is covered with a
material called slope protection, which should be both aesthetically
pleasing and provide for proper drainage and erosion control.
BRIDGE COMPONENTS: APPURTENANCES AND
SITE-RELATED STRUCTURES
Slope protection could be made of dry stone or even block pavement
material.
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SITE-RELATED STRUCTURES
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SITE-RELATED STRUCTURES
BRIDGE COMPONENTS: APPURTENANCES AND
SITE-RELATED STRUCTURES
v Underdrain. In order to provide for proper drainage of a major
substructure element, such as an abutment, it is often necessary to
install an underdrain, which is a drainage system made of
perforated pipe or other suitable conduit that transports runoff
away from the structure and into appropriate drainage channels
(either natural or man-made).
BRIDGE COMPONENTS: APPURTENANCES AND
SITE-RELATED STRUCTURES
v Approach. The section of overpass roadway which leads up to and
away from the bridge abutments is called the approach or approach
roadway. In cross section the approach roadway is defined as the
“travelled way plus shoulders.”

To compensate for potential differential settlement at the

approaches, a reinforced concrete slab or approach slab is
sometimes used for a given distance back from the abutment.

The approach slab helps minimize impact to the abutment which

can result from differential settlement. It is possible for the
approach to be physically supported by the abutment.
BRIDGE COMPONENTS: APPURTENANCES AND
SITE-RELATED STRUCTURES
v Traffic Barriers. Protective devices used to reduce the severity of an
accident when a vehicle leaves the road are called traffic barriers.

Traffic barriers can range from a guard rail made of corrugated steel
to reinforced concrete parapets.
BRIDGE COMPONENTS: APPURTENANCES AND
SITE-RELATED STRUCTURES
BRIDGE COMPONENTS: IN SUMMARY
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TYPES OF BRIDGES
vTypes of bridges can be classified according to the
following:
vBy Materials
vBy Objective
vBy Structural System
vBy Support Condition
vBy Position of Travelled Roadway
vBy Durability
TYPES OF BRIDGES
v Classification by Materials

v This classification is based on the main type of the construction

material used for the superstructure.

q Steel bridges: A steel bridge may use a wide variety of

structural steel components and structural systems such as
girders, frames, trusses, arches, and suspension cables.
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v Steel bridge:
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v Concrete bridges: There are two primary types of concrete bridges:
reinforced concrete and prestressed concrete.
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v Concrete bridges:
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v Timber bridges: Wooden bridges are used when the span is
relatively short. In some cases, timber bridges are used as
temporary bridge structures.
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v Metal alloy bridges: Metal alloy such as aluminum alloy and stainless
steel can be used in bridge construction.
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v Classification by Objective
v This classification is based on the
type of load that is carried across the
bridge. Bridges can alternatively be
classified into movable (for ships to
pass the river) or fixed and
permanent or temporary categories.
q Highway bridges: bridges on
highways for vehicles.
q Railway bridges: bridges on
railroads for trains.
q Combined bridges: bridges
carrying both vehicles and
trains.
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q Pedestrian bridges: bridges
carrying pedestrian traffic.

q Aqueduct bridges: bridges

supporting pipes with
channeled water flow.
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v Classification by Structural System of
v Superstructure This classification
is based on the structural system
of the main girders of the
superstructure.

q Plate girder bridges: The main girders

consist of a plate assemblage of
upper and lower flanges and a web.
H- or I- cross-sections are used to
effectively resist bending and shear.
TYPES OF BRIDGES
v Box girder bridges: The
simple (or multiple) main
girder consists of a box
beam fabricated from steel
plates or formed from
concrete, which resists not
only bending and shear but
also torsion effectively.
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v T-beam bridges: A number of reinforced concrete T-beams are
placed side by side to support the live load.
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q Composite girder bridges: The
concrete deck slab works in
conjunction with the steel
girders to support loads as a
united beam. The steel girder
takes mainly tension, while the
concrete slab takes the
compression component of the
bending moment.
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q Grillage girder bridges: The main girders are connected transversely
by floor beams to form a rid pattern which shares the loads with the
main girders.
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q Truss bridges: Truss bar members are theoretically considered to be
connected with pins at their ends to form triangles. Each member
resists an axial force, either in compression or tension.
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Typical types of truss bridges are:
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q Arch bridges: The arch is a structure that resists load mainly in axial
compression.

The circular arc in compression supports the road; the

arch can either be below or above the road.

In ancient times, stone was the most common

material used to construct magnificent arch bridges.
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q Arch bridges:
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q Cable-stayed bridges: The girders are supported by highly

strengthened cables (often composed of tightly bound steel
strands) which stem directly from the tower. These are mostly
suited to bridge long distances.

The cables in tension support the road (or superstructure).

TYPES OF BRIDGES
q Cable-stayed bridges:
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Bunker Hill Bridge, Boston
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q Suspension bridges: The girders are suspended by hangers tied to
the main cables which hang from the towers. The
load is transmitted mainly by tension in cable.
The cables in tension support the road (or
superstructure). This design is suitable for long
span bridges.
TYPES OF BRIDGES
q Suspension bridges:
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v Classification by Support Condition

v This classification is based on the support conditions of a bridge.

q Simply-supported bridges: The main girders or trusses are

supported by a movable hinge at one end and a fixed hinge
at the other end (simple support); thus they can be analyzed
using only the conditions of equilibrium.
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q Continuously-supported bridges: Girders or trusses are supported
continuously by more than three supports, resulting in a structurally
indeterminate system. These tend to be more economical since
fewer expansion joints, which have a common cause of service and
maintenance problems, are needed. Shrinkage at the supports must
be avoided.
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q Gerber bridges (cantilever bridges): A continuous bridge is rendered
determinate by placing intermediate
hinges between the supports.
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v Classification by Position of Travelled Roadway

v This classification is based on the position of the bridge floor

with respect to the main girder or main supporting the
structural member.

q Deck: When the roadway is on top of the main girder.

TYPES OF BRIDGES
q Pony: When the roadway is next to the main girder.
TYPES OF BRIDGES
q Half-through: When the roadway is between the depth of the main
girder.
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q Through: When the roadway is at the bottom of the main girder
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v Classification by Durability
v This classification is based on the duration for which the bridge
is intended to be useful.
q Permanent bridges
q Semi-permanent bridges
q Temporary bridges