Lecture 01 PPT

CIEM 5380
BRIDGE ENGINEERING
Dr. Barry K.W. Lee, B.Eng, M.Phil, Dr.-Ing, MICE CEng
14 September 2012 Bridge Construction Engineering
General Information
 Class : CIEM 5380 – Bridge Engineering

 Venue: : Room 4620
 Schedule : From 14 September 2012 (Every Friday)
 Email : ciem5380@ust.hk
 Assessment:
 2 written Assignments, 10% each, total 20%
 1 mid-term Examination, 30%
 1 final Examination, 50%

Course Contents
 Construction Engineering
 Structural Forms
 Loading on Bridges
 Introduction to Eurocode Bridge Design
 Analysis
 Detailing
 Bridge Accessories
 Special Topics
 Planning and design of sea crossing
 Long Span Bridges
 Ship Impact & Bridge Aerodynamics
 Seismic
 Structural Health Monitoring System
About me
 UST 2nd Batch Graduate
 Educated in Hong Kong and Germany
 Germany, Denmark, Hong Kong, Singapore, Mainland
China, Brunei, Qatar, Bahrain, Vietnam, Panama, Turkey
and Venezuela
 Major Project Experience:
 Route 8 Ngong Shuen Chau Viaduct
 Stonecutters Bridge
 Qatar Bahrain Crossing
 Maracaibo 2nd Crossing
 Izmit Bay Crossing
 Fehmern Belt Sea Crossing
 Tuen Mun - Chek Lap Kok Link
Project Photo
Project Photo
Introduction to Construction Engineering
 Why we need to know how bridges are

built at this stage?
 Close Link between designer’s choice of
bridge deck type and bridge structural
form.
 Cater for site constraint
 Better cost estimation because labor and
plant are two principle components of cost
built up besides materials.
 Avoid collapse/unexpected behavior during
erection (CSB over River Chambal and
Indian River)
Insitu Construction on Falsework
 Basic Bridge Construction Method
 Provides the designer with the greatest degree of
flexibility with regard to the shape and form of the
structure
 Suitable for bridges built over land
 Not suitable for bridge over water
 Temporary foundation over water is very expensive
Classical Scaffolding
Stationary Falsework
Launching Systems
 Particularly design for precast segmental erection
 Cost economy span range: 30m to 70m.
 Time saving
 Precast yard factory like segment production can
ensure good quality control and constant production
rate.
Launching System
Launching gantry for balanced cantilever construction
Launching System
Launching gantry for balanced cantilever construction
Animation on operation of Launching Girder

Launching System
Launching gantry for span by span construction
Balanced Cantilever Construction
 Span range from 50m to 200m or even up to
300m
 Assembling segments by building outwards
from the piers.
 Each segment is prestressed as soon as it has
been placed, thereby enabling it to support
itself by cantilevering from its predecessor.
 Reduce temporary supporting system
 Two types of balanced cantilever methods are
commonly used:
 Cast-in-situ balanced cantilever construction
 Precast segmental balanced cantilever construction
Cast Insitu Balanced Cantilever Construction
 It is ideally suited to box section bridge of

medium to long span, where the total bridge
length is not long enough to justify using precast
segments.
 Form traveler is
normally used
 Prestressing
arrangement
Precast Segmental Balanced Cantilever Construction
 Segments can be erected by crane,

launching gantry or lifting fame
depending on scale of the bridge,
weight of the segment and most
importantly the site constraint.
 Feasible span range is 30m to
70m. World record is 150m (very
unusal)
 Concrete age are several weeks
older or even longer when they are
erected. (what is the implication?)
 A considerable proportion of the
shrinkage of the concrete will also
be completed before erection.
(what is the implication?)
Span by span
 It can either be cast insitu or precast segmental
 Simply supported system is used.
 Continuity slab is used widely in America and
middle east to improve the riding comfort.
Incremental Launching
Incremental Launching Animation
 Typical span range is around 30m to

55m.
 Longer span is feasible but intermediate
support is required.
 Construction rate is approximately 15 to
25m per week.
 Conventional launched bridge decks
require typically up to 20% more
prestressing steel than bridge built by
other methods. (Why??)
Precast Beams
 A mature bridge form used anywhere in

Australia.
 Maximum 40m span (using Australia
super T beam).
Comparison
Span Range [m] Construction Speed [metres/week]
0 100 200 0 50 100 150 200
(1) Classical scaffolding and stationary falsework
(2) Launching Girder/Gantry
- In situ concrete construction
- Precast elements
(3) Precast beam
(4) Cantilever
- In situ concrete construction
- Precast elements
(5) Incremental launching
- without temporary support
- with temporary support
(7) Heavy lifting

INFLUENCE OF THE METHOD OF CONSTRUCTION ON DESIGN
Construction on Scaffolding or Falsework
 Economically use of scaffolding

(1) Structure is to be constructed over land and when the
ground conditions are good.
(2) Structure is relatively close to the ground,
(3) Structure is of modest length,
(4) Settlement of soil due to superimposed dead load is very
little,
(5) No major obstacles to be crossed by falsework
 Example of a 2 spans bridge

Balanced Cantilever
 The length of the cantilevers will be approximately half the span

length on either side of the pier.
 Once the crew overcame the learning curve, 3 pairs per day
production rate in Hong Kong construction site can be achieved
 It would obviously simplify the construction if the end span were
to be half the length of the adjacent span, however this
arrangement would result in uplift of the bearings at the end of
the bridge due to the action of traffic live load.
 One way to avoid this is to increase the length of the end span by
means of increasing the length of end span, those addition length
(against the balanced cantilever length shall be erected the
precast on falsework.
Balanced Cantilever
 For haunched bridge, 60% of the main span length is a good ratio
to avoid uplift.
 For constant depth, 70% of the main span length is adopt
 Discussion:
What happen if the end span cannot be longer than the figure
mentioned above?
 Support System:
Pros and cons of bearing support system?
Pros and cons of monolithic system?
Balanced Cantilever
 Design Considerations:
 Single box or multi-box?
 Top Slab Thickness?
 Web thickness?
 Prestressing System
 Cantilever tendons
 Continuity tendons
 External tendons
Incremental Launching
 Only for constant depth (i.e. not suitable for bridge with haunch)
 Alignment of the bridge need to be straight or on a constant
circular curve.
 Feasible deck type:
1. slabs
2. ribbed slabs
3. single/multiple box girders (preferred, will be elaborated in
prestressing design)
 Prestressing Design:
Stage 1: Straight tendons in top and bottom slab.
Stage 2: Profile continuity tendons

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CIEM 5380

 Class : CIEM 5380 – Bridge Engineering

 1 final Examination, 50%

 Why we need to know how bridges are

Animation on operation of Launching Girder

 It is ideally suited to box section bridge of

 Segments can be erected by crane,

 Typical span range is around 30m to

 A mature bridge form used anywhere in

Span Range [m] Construction Speed [metres/week]

0 100 200 0 50 100 150 200

(1) Classical scaffolding and stationary falsework

(2) Launching Girder/Gantry

- In situ concrete construction

(3) Precast beam

- In situ concrete construction

(5) Incremental launching

- without temporary support

- with temporary support

(7) Heavy lifting

Construction on Scaffolding or Falsework

 Economically use of scaffolding

 Example of a 2 spans bridge

 The length of the cantilevers will be approximately half the span

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