construction of bridges - city university of hong...

Construction of Bridges

Materials suitable for the Construction of Long-span Bridges

1. Stone – in arch masonry

2. Steel – in girder or box-section constructed in steel plates and standard sections

3. Steel – truss constructed of standard sections

4. Reinforced Concrete – in arch or spanned forms

5. Tensioned RC – in various forms

6. Precast – mainly in box-section girder

Common Bridge Forms

Simple Supported – span effective from 10m to 60m

Actual example – Route 3 Interchange at Au Tau, Yuen Long

Continuous Span – from 10m to 100m

Actual example – construction of a span of continual section of elevated highway bridge at Route 3, Kwai Chung

Balanced Cantilever – span from 25m to 200m

Actual example – balanced cantilever bridge series forming the approach to the Ting Kau Bridge

Balanced cantilever bridge for viaduct of West Rail at Au Tau Interchange

Balanced Cantilever Suspended Span – span from 50m to 300m

Steel Truss – 50m to 100m

Actual example –5-span steel truss bridge in western part of Pearl River, Guangzhou

Steel Arch (framed or trussed) – from 150m to 500m

The Sydney Harbour Bridge and its approach

Cable suspension – from 400m to 1500m

The 1377m span TsingMa Bridge

Concrete Arch (ribbed or unribbed) – from 50m to 300m

Steel Arch – from 100m to 500m

Cable stayed (multi-spanned) – from 50 to 500m per span

The 3-span cable-stayed Ting KauBridge

Cable stayed span – from 200m to 800m

Actual example – the connecting bridge from Macau Mainland to the Island of Taipa in Macau

Example of box-sectioned steel girder bridge

Structural Elements for Typical Bridges1. Foundation –for bridge towers, portal frames or piers

2. Bridge Tower – the vertical supporting structure for cable suspension or cable-stayed bridges

3. Portal frame or pier – the vertical supporting structure for usual spanned bridges

4. Bridge deck – the horizontal part of a bridge that support pedestrian or traffic activities

5. Bridge anchor – required only for suspension bridges to counter resist the pull from the suspension cable

6. Suspension cable – for suspension and cable-stayed bridges for the hanging, support or counter-balancing of the bridge deck

The foundation of the bridge tower of Ting Kau Bridge on Tsing Yi side

The foundation for the Bridge Tower of Tsing Ma Bridge on the Tsing Yi side

Forming the foundation for piers of elevated highway bridges

Pier supports for an elevated roadway

A portal frame serving also as a transfer beam in the Route 3/Airport Railway at Kwai Chung

Bridge tower for Tsing Ma Bridge and Kap Shiu Mun Bridge

Tsing Ma Tower

The forming of the cable anchor of Tsing Ma Bridge on Ma Wan side

The forming of the cable anchor of Tsing Ma Bridge on Tsing Yi side

Forming the deck of the approach section of TsingMa Bridge on Ma Wan side using erection and hoisting approach

Forming the deck of the approach section of Tsing Ma Bridge on Tsing Yi side

Completing the deck of Tsing Ma Bridge (abutting section at Tsing Yi side) by erecting of the steel truss at spot

Hoisting and erecting of the modulated bridge deck for the Tsing Ma Bridge

Forming the bridge deck of Ting Kau Bridge using modulated steel girder frames

Laying the precast deck of the steel girder frame

Other methods to form the deck of bridges

1. Balanced cantilever method

2. Construct in-situ

3. Construct using precast beam

4. Construct using precast girder section and erected by a launching machine (viaduct)

5. Construct using incremental launching method

Forming the deck of the Ting Kau Bridge approach section using a special balanced-cantilever traveling formwork system

The Ting Kau Bridge approach section

Construction of a section of elevated railway track in the KCR Ma On Shan Line using in-situ method

The laying of precastbeams to form the deck of the Route 3 elevated roadway at Kwai Chung

Hoisting of the precast beams using a special launching gantry

Construction of an elevated highway bridge using precast girder erected by the use of a launching machine

Launching gantry used to erect precast girders to form a span of an elevated bridge (viaduct)

A bridge in the Fo Tan Road Improvement

Project making use of Incremental Launching

method to span across the servicing KCR rail line

Alignment of servicing rail line

– elevated roadway constructed in the form of viaduct

Route 3 – Kwai Chung Section

Route 3 – Country Park Section at Au Tau Interchange

Hung Hom Bypass

Tsing Yi North Coastal Roadway

Highway project in Ma On Shan

Launching gantry used in the Hung Hom Bypass

Launching gantry used in Route 3 at Au Tau Interchange

Launching gantry used in Tsing Yi North Coastal Roadway

Launching gantry used in the Ma On Shan highway project (T7)

Launching Gantry used in the Route 3 Kwai Chung section

A review of other highway and railway bridges

– construction of the viaduct systems for the West Rail projects

Viaduct for railway track of the KowloonCanton Railway West Rail at the northwesternpart of the New Territory, Hong Kong

Some sections of viaduct spanning more than 40m at Au Tau Interchange

Forming the viaduct for railway track using the under-slung girder and longitudinal beam supported method

Erection of the viaduct using balanced cantilever arrangement with temporary anchor before completion of a span

Precast box girders used for the viaduct

A section of viaduct with provision for an extension to the future northern link

Construction of some sections of elevated railway track using in-situ method

Constructing the linking bridge between Tung Chung and Chek lap Kok(the Airport Railway) using Incremental Launching method

Principle of viaduct construction using segmental launching

(by Launching Machine)

Front leg

Master winch

Rear leg

Slave winch

Rear support

Hangers Front support

116m longMain Truss

(For end span and 1st pair segment erection)(SWL = 105 T)

(SWL = 120T)

Elevation of the Launching Machine

Typical installation of the precast box-girder to form the viaduct:

Install the 1st Pair Segment By The Launching Machine with Hangers

1st pair segment preassembled on ground, ready to be lifted up by master winches.

a) Stitching platform and rebar cage

b) Hanger frame

c) Stressing Platform

FIRST PAIR SEGMENTS LIFTING(WITH FORMWORK AND STRESSING PLATFORM)

Hang the 1st pair segments to launching girderAfter fine adjustment, cast the stitch concrete

FIRST PAIR SEGMENTS IN PLACE

Perform the tendon stressing, load transfer from LG to Portal Pier

Remove the platforms

FORMWORK REMOVAL

FIRST PAIR SEGMENTS STITCHING COMPLETED

Typical installation of the precast box-girder to form the viaduct:

Continue to erect the segments pairs by pairsUsing balanced cantilever principle

LIFT SEGMENT FROM GROUND TO ERECTING POSITION

Lift and erect the next precast segmentApply epoxy glue to the match cast face and temporary stressing.

Erect the conjugate segment pair;After application of cantilever tendon, load transfer to pier completed;

A section of viaduct erected in a balanced cantilever manner

Continue the segment erection for the rest segment pairs

Completion of a spanHang the end span segments with hanger frameAdjust the geometry of the hanging segmentsConcrete the stitch jointsPerform the span tendon stressing when concrete has developed the

required strength,.Load transfer to pier or portal completed, released the hangers

Typical Span

End-span erection with the use of hanger to support the precast box from the launching girder

Trends in the Construction of Bridges in HK

Construction of large and long-span bridges is of no doubt a part of the major infrastructure development for a city, which is, again, a reflection of the economical climate and development strategy of the area.

On the construction side, the limited land reserve in Hong Kong does imposes stringent conditions especially where the options and cost effectiveness of constructing a bridge is concerned. To cope with these considerations, a few world-class bridges over 1000m span are yet scheduled for completion in the coming decade, in view of keeping Hong Kong to be competitive in particular within the highly economic-active region in the southern part of China. The construction of these bridges is, without much choice, in the form of either cable-stayed or suspension bridges.

The construction of other medium to short-span bridges are becoming much popular recently as part of the highway improvement strategy in Hong Kong.

The shortage of space for highway improvement works, the involvement of complicated interchanging provisions, the familiarization of bridge construction techniques in catering various local constraints with acceptable cost, are factors that made bridges of this type becoming popular.

Some inherited difficulties such as the requirement of large amount of working spaces for the forming, transporting and storing of the roomy precast elements; the operation of the launching works, or arrangement for traffic diversion within existing busy roadway, still makes roadwork under urban environments complicated and costly. Needless to mention working in environmental sensitive locations such as where protection to natural habitats or rural culture is required; or where waste, noise and dust problems are of ultimate concern.

The cost for constructing bridges are unavoidably high in particular working within congested and complicated urban environment like Hong Kong.

As a tradition, bridges and elevated highway structures in Hong Kong are mainly constructed in concrete. As a cost saving option, steel bridge, say, in hollow section, box-girder or any other feasible design, may be alternative choices for highway bridges,like those commonly used in Mainland China or Japan. The saving in initial cost and construction time of using such alternatives may provide surplus capitals and expedite the ongoing infrastructure projects, this is essential especially in the forthcoming years when the economic situation is expected to be less favourable than before.

The end of the presentation