Composite Bridges using External Prestressing
External pre-stressing has been used not only in concrete bridges but also in composite bridges either in classical composite bridges or in new type of bridges with different ways associating concreting and steel.
The use of pre-stressing concrete box girder bridges with corrugated steel webs is being constructed widely considering the cost effectiveness to construct new bridges. In these structures, the concrete webs are placed with corrugated steel plates to reduce the self weight which also simplifies the construction.
Figure below shows the typical section of a pre-stressed concrete bridge with corrugated webs. Basically, the pre-stress is provided by means of bonded tendons arranged in the upper and lower flanges of concrete slab and unbounded external tendon for webs, since the webs are made of steel plates. It is studied and concluded that a reduction of self weight of about 25% can be achieved in this kind of structures compared to conventional PSC box girder bridges.
Number of bridges with corrugated steel webs has been constructed worldwide. Some examples of such bridges constructed will these techniques are described below:
Typical section of a Pre-stressed concrete Bridge with Corrugated Webs
The Givizon-Miyuki Bridge has five spans with a total length of 210m, which was the first bridge to be constructed in Japan using incremental launching method. Weathering steel plates were used for the web. The feature of this bridge is that stud dowel connectors were adopted for the connection between concrete and steel plate. Further, the connection between steel plates in the direction of the bridge axis was by means of bolt connection of the end plates. This method was adopted considering the aesthetic appearance of the bridge.
The Shivasawa Bridge has a span of 50m was also constructed in Japan using supported formwork. The unique feature of this bridge is that “perforbard” connection was adopted for the first time in Japan to connect the steel web and lower flange of concrete slab.
The Kogawauchi-gawa Bridge with a total length of 160m was constructed by the cantilever launching method. Pointed steel plates were used for the web.
The above examples illustrate by the use of external pre-stressing how composite bridges can be designed to enhance better performance by effective use of materials such as steel and concrete.
Complete View of Shirasawa Bridge
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