DYWIDAG Multistrand Tendons Stabilize Japan’s Longest Plate Stayed Bridge

In 1994, work began on the Yamba Dam, the largest hydroelectric power project in Japan in terms of value. The structure will dam the Agatsuma River on Japan’s main island, submerging part of the Agatsuma railway line.

Consequently, approximately 10.4km of the railway line had to be relocated.

The second Agatsumagawa Bridge is part of this relocation project. The railway bridge, located near the final stop on the Agatsuma Line, curves to the left with a 600m radius, and crosses National Route 145 and the Agatsuma River. One half of the structure consists of prestressed concrete box girders, and the other half is a three-span continuous box girder plate stayed bridge.

The bridge is the first plate stayed bridge in Japan to feature concrete plates with curved surfaces. Its 167m center span makes it the longest bridge of this type in Japan. The main girders have a box girder cross section with rigid ribs, while each main pylon consists of four independent columns - a combination rarely encountered in bridges anywhere in the world.

During the construction of the three-span continuous stayed plate bridge, the cantilever construction method was used to cast 3m long blocks in the center span using a form traveler, while the fixed support method was used to cast 6m long blocks in the side spans. The primary diagonal cables supporting the main girder were installed with a winch and a crawler crane as cantilever construction proceeded. The secondary diagonal cables with a maximum length of 140m and rising gradient of approx. 30% were added after connecting the main girder using two interlocking pushing machines.

Once the concrete plates had been positioned, they were post-tensioned and the temporary supports of the girder were released. Since the primary diagonal cables would be left exposed to the atmosphere for approximately one year, Sumitomo supplied Type 12S15.2MA DYWIDAG Strand Tendons with epoxy coated strands to prevent corrosion. Type 12S15.2MA DYWIDAG Strand Tendons with bare strands were used for the secondary interior diagonal cables which would be grouted at the end.