Extradosed bridge with lightweight butterfly web structure (Mukogawa Bridge)
One of the features of Mukogawa Bridge is the combination of the butterfly web structure*3 in the main girder with the extradosed structure*4, which was the first attempt in the world. Mr. Katsuhiko Mizuno from Sumitomo Mitsui Construction Co., Ltd. was in charge of the design and construction.
"We had to thoroughly reduce the weight and improve the earthquake resistance. The amount of concrete and steel used in a bridge can be reduced with the butterfly web structure due to its shape as well as with the extradosed structure, which uses shorter main towers (girder height of 4 m). A lighter bridge girder leads to higher earthquake resistance and can also slim down the foundation and piers, which can eventually improve the economic efficiency and reduce the environmental impact. We needed the high-strength prestressing steel strands to meet these requirements. "
As a result of reducing the weight of the main girder, we decreased the total number of the blocks in free cantilever construction (bridge erection method to extend the bridge body from each pier to both directions; the width of a block is usually 3 to 4 m). It helped reduce the construction work as a whole, shorten the construction period and thereby lower the environmental impact.
"The bridge would not have been achieved without the high-strength prestressing strand and the anchorage system. Sumitomo Electric did not only supply prestressing steel strand and the anchorage system but also responded to various technical issues on the construction site. They are a reliable partner."
*3 Structure with butterfly-shaped thin panels
*4 Bridge structure where diagonal cables anchored to the main towers support the bridge girder
For Aigawa Bridge, the prestressing steel strand had to have higher strength. The span length of the bridge (span between the piers) is 179 m for the inbound lane and 170 m for the outbound lane and the maximum girder height of the piers is 11.5 m. It is the world's top corrugated steel-plate web girder bridge in terms of both span length and girder height. To establish the structure of Aigawa Bridge, the reduction of the weight was a major challenge. Mr. Naoki Nagamoto from Sumitomo Mitsui Construction, who was in charge of the design and construction, also mentioned it.
"The reduction of the weight is always a major proposition for bridge engineers like us. How we can reduce the amount of concrete is a theme we have tackled as a pioneer of concrete bridges for many years. In the case of Aigawa Bridge, it was difficult to arrange prestressing steel cables because a very large number of prestressing steel cables were needed to support the dead weight of the bridge with a very long span. Then, we adopted the super-high-tension system to reduce the number of cables by about 20% and were able to establish the world's longest structure."