Yabegawa Bridge: Japan’s Longest Cable-Stayed Prestressed Concrete Bridge

The Yabegawa Bridge forms part of the Ariake Sea Coastal Road along the Ariake Sea in southern Japan.

The three-span, continuous cable-stayed prestressed concrete bridge crossing the Yabe River is 19m wide and features a 261m center span as well as two side spans of 128m each. With a length of 517m, the Yabegawa Bridge is the longest cable-stayed prestressed concrete bridge in Japan.

The Yabegawa Bridge is curved – a feature that is very rare for a bridge this size. The project is characterized by many different technical features. These include an inclined inverted-Y-shape main pylon structure, a trigger-type stopper structure, very deep pneumatic caissons, the use of a massive form traveler for cantilever erection, and the use of an elevator-type movable scaffold for the main pylons.

To improve construction efficiency, the main girders were built using 8m long segments that were positioned using a massive form traveler weighing approximately 300t. Since each segment was 8m long instead of the usual 4m, construction time was shortened by five months at an installation rate of approx. 17 days per segment. In order to establish a reduced cycle time, the cantilever construction method for the segments positioned right and left was also adjusted accordingly, and the support structure was specially designed. 44 to 48 Type SBPR 930/1180, Ø 32mm DYWIDAG Post-Tensioning Bars supplied by Sumitomo were installed per section for cantilever segment alignment and tensioning.

The bridge was erected in an area with very soft clay soil. Therefore, construction of the bridge involved extensive studies and special measures to account for the settling of the main pylon foundations during work on the superstructure. One of these measures consisted in using high-strength external tendons for effective reinforcement against unexpected settlement.

The Type 19S15.7MC Ø 15.7mm DYWIDAG Tendons consisting of epoxy coated and filled strands with HDPE sheathing also served to reinforce the main girder. With a guaranteed tensile strength of 2,250MPa, these strands are the highest strength strands used in post-tensioning worldwide. Compared to the Type 19S15.2 DYWIDAG Strand Post-Tensioning System originally proposed for the bridge, the system used offers approx. 20% more stress resistance and approx. 28% more load resistance.

The stronger external tendons maintain main girder strength against uneven settlement of the main pylon foundations of up to 10cm. The steel used in the hightensile strands, the performance of the anchoring system, and safety margins provided by the concrete were tested and analyzed to confirm the suitability of the individual components.

The tendons were 269m long in the center span and 131m long in the side spans. There was only little space to insert the 269m tendons inside the girder and to post-tension them. All of the tendons in the side spans were stressed conventionally at the end support using a multi-strand jack. For the tendons in the main span, strands were stressed individually using a monostrand jack due to limited working space. Thanks to this procedure, construction was carried out efficiently. The Yabegawa Bridge was completed in early March 2009, and traffic now flows freely on a 23.8km long section between Omuta City and Okawa City.