Use of a new Bridge Cost-effective Construction Method
The route between the Shizuoka and the Fujieda- Okabe interchanges is built through mountainous territory with large changes in elevation. Such topography promotes innovative ideas with regard to the chosen bridge construction method, since construction of the piers can be very difficult. For the Katsurajima Viaduct, a slightly modified incremental launching method was chosen.
The Katsurajima Viaduct was erected at Katsurajima in Okabe-cho, Shizuoka, in only two years as part of the New Tomei Expressway between the Shizuoka Interchange and the Fujieda- Okabe Interchange.
To maximize the efficiency of incremental launching and to cut costs, the main girder was constructed in stages, with only the core section being launched incrementally. A one-cell box girder cross-section with corrugated steel webs was selected to reduce the weight of the incrementally launched units. After launching, the cross-section was extended to achieve the width required for the bridge slabs. For this purpose, correspondingly wide precast panels were used as permanent formwork that were supported by the ribs and struts added to the hollow box girder. The final bridge deck was cast-in-place.
The Katsurajima Viaduct was the first bridge in the world to use this construction method. This method involving a conventional hollow box girder with a corrugated steel web makes it possible to use a smaller bottom slab since the overhang of the bridge deck is supported by ribs and struts. As a result of using a corrugated steel web instead of concrete, the main girder weight is reduced by about 30%.
Only the core section of the main girder is launched incrementally. The over hanging parts of the bridge deck are added later. This reduces the weight during the installation of the girders to about 50% of the conventional weight, which in turn lowers the requirements for the launching nose, jacks and other erection equipment. It also reduces the amount of prestressing steel required for the main girder.
This newly developed method is very efficient due to its lower cost and reduced work load.