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span-by-span method of bridge construction

precast segmental bridge construction can effectively reduce the time of bridge construction, reducing the time of construction mean minimizing the disturb to road commuter and neighbors, also increase the quality of constructed bridge, the reason for the increase in bridge quality is due to high-quality controls in factories that produce precast segments. on the other hand, this type of construction required skilled workmanship and special equipment not available for certain regions.

Figure 1

Precast segmental bridges may be erected with four construction methods: span-by-span erection with self-launching gantry; balanced cantilever erection with ground cranes, lifting frames or self-launching gantry; progressive placement with a cable-stayed system or temporary piers; and incremental launching. The development of external post-tensioning contributes to the increase of using the span-by-span construction method. this method is cost-effective, rapid construction method and can be used for long bridges (25 to 45 m) with large plan radius. 
Figure 2

Deck constructed starts at abutment towards the piers. segments placed at the end of each other until one span is completed. segments will be placed and held in the correct location using temporary staying mast system or more commonly assembly truss. before beginning with launching and placing of segments, assembly truss will be braced to piers. then segments will be placed in the correct location using sliding bads, expoy will use to close and joint segments.

after the completion of placing all the segments for one slab, post-tensioning tendons are placed inside ducts and the whole span will be stressed.


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