Span by Span Precast Segmental Construction
As part of Land Transport Authority's effort to improve the road network in Singapore, an elevated expressway in the north eastern part of Singapore is currently under construction. This expressway will provide a direct traffic link from the industrial area of Paya Lebar to Tampines,one of Singapore's biggest new towns.
This 2 km long elevated viaduct, Airport Road-Tampines Avenue 10, typically has a span of 45 m. Instead of utilizing a more typical construction arrangement of two separate piers and individual box girders to accommodate different directional flow of traffic, this dual three-lane carriageway consists of a triple cell box girder, with cantilever wing slabs attached to both sides of the box girder supported by individual piers.
Utraco Structural Systems Pte.Ltd., the DSI representative in Singapore, was contracted to launch the precast segments using a double triangular truss and to supply and install both internal and external post-tensioning tendons. The company was also awarded the in situ construction works of the bridge deck's parapet, flower trough and cross head stitching.
Each typical span has a total of 13 precast triple cell segments weighing a 1,000 t. DYWIDAG THREADBARS® are used extensively during the construction to facilitate lifting of the segments and the temporary stressing operation. They are also employed for the lifting and suspending of the main segments by the launching gantry, temporary stressing of the main segments, and holding in place of the cantilever wing slabs prior to the casting the pour strip and stressing the slab transverse tendons.
In the box girder design,the engineer has opted to use both internal and external tendons. Stage 1 stressing involves the stressing of internal tendons (made up of generally eight 12 to 19-0.6" strand tendons) while all the precast main segments are held in place by the launching gantry. Stage 2 stressing, which is made up of generally four 19-0.6" external tendons, is performed after the casting of the in situ crosshead. Stage 3 stressing would only commence after both sides of the cantilever wing slab are in place.
The project was successfully completed in November 2003.