Steel Bridge Cantilever Erection

STEEL BRIDGE ERECTION MULTI SPAN BRIDGE WITH CANTILEVER METHOD

This presentation will explain the procedure of erection steel bridge using cantilever method from design concept to the work execution

Prepared by Adhi Triono © 2008

BACK GROUND
The erection of multi span bridge is required certain method due to the difficulty of the

erection by using prop/support method by considering the time, cost, high of river bed, etc.
Generally the erection of multi span bridge is whether using launching method or

cantilever method.
The beneficiary of cantilever method is that this method not required special equipment

compare to launching method which is required more sophisticate equipment such as huge electric winch or hydraulic jack, wire rope, etc. Therefore, this cantilever method is less expensive, less on risk, and faster.

Design Stage

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Structure Remodeling
Check original design criteria, if the original design criteria has not considered

the cantilever method, then the structure has to be remodeling.
Due to the cantilever method than the member of the steel bridge has to be

checked carefully whether the member is strong enough to restrain the stresses occurred.
The remodeling of the steel bridge is better using a software which is available

at the marker such as STAADPro, SAP, or other software for time saving and also for the accurate result.
The load has to be considered for remodeling is:
Dead Load
Rail Load (for transporting the steel member and also for crane)
Crane for erection
Wind Load
Others load which might occur during erection

Post Remodeling
Axial force (tension or compressed force) of each member and then calculate

the stresses and compare to allowable stresses, in case the actual stress is exceeding the allowable stress then the member has to be strengthened by increasing the net area. Notify the Engineer in case the member has to be strengthened. The stress check has to be done for both span (the cantilever span and the counterweight span)
The deflection of the bridge for each node/joint. The result has to be

superimposed with the designed camber of the bridge so the final result will not deviate with the camber requirement. The designed camber can be found on the drawing or inquire the data from the Engineer (in case those information cannot be found on the drawing).
Design of Link Member, “Link member” mean the temporary steel member for

linking of 2 span of the bridge so the 2nd span of the bridge will become cantilever.

Stage 1


Erect the Dummy span on Bent Support (this span will be dismantle afterward) on

the approach formation. Fixing the joint by temporary bolts.
Install the crane on the upper chord rail.
Install steel link for the erection of the 1st span (next span)

Stage 2


Erect the span 1, steel material is supplied from the stockyard to erection area







using trolley system. Fixing joints by permanent bolts. Kentledge must be kept ready prior to erection steel girder near end portion (as a counterweight). The load of kentledge approximately 33% of total weight a single span of steel girder. Provide steel link prior to start erection of the next span. The dummy span can be dismantle and the erection can be continue to the next span to the end.