New Combination of Extradosed and Butterfly Web
The Shin-Meishin Mukogawa Bridge is located north of Kobe is the world’s first bridge to have been designed as an extradosed bridge combined with butterfly shaped webs for the main girder. This design concept greatly reduced the structure’s weight and enhanced its earthquake resistance.
The 442m long extradosed bridge with a continuous rigid frame and butterfly webs includes three 100m long spans. The weight of the superstructure was reduced by butterfly shaped precast concrete panels that are installed at defined distances. Thanks to the reduced weight, the cross section of the piers was reduced to create a slender pier configuration.
The height of the girder was limited because transportation restrictions between the precast factory and the jobsite dictated the maximum size of butterfly panel that could be accommodated. In order to achieve a span length of 100m and to bring the girder to the desired height, the bridge was designed as an extradosed bridge.
The use of the SPER Method (Sumitomo Precast form for resisting Earthquakes and for Rapid construction) in the pier structure ensured a rapid construction progress through labor saving. In this method, stay-in-place precast concrete panels are used both as segments and as formwork for cast-in-place concrete. In order to save labor and shoring for the pier heads, a section of the crossbeams was precast.
The main tower is located in the median strip between the lanes so that the available space in the hollow box girder was not as large as in the case of stay cable bridges. Consequently, Sumitomo developed a new, isolated anchor system consisting of a single steel plate and two independent pillars that can also be installed in narrow spaces.
Type 12S 15.7 MC and 19S 15.7 MC DYWIDAG Strand Tendons with high-strength (2,230MPa), epoxy coated and filled strands were used as external tendons. In order to protect the external tendons from the ultraviolet rays coming in through the web panels’ openings, the strands are covered with HDPE sheaths.
The high-strength Type 19S 15.7 MC DYWIDAG Strand Tendons were also used as extradosed tendons outside the box girder.
The main girders were constructed with Type 12S 12.7 MA, 12S 15.2 MA and high-strength Type 12S 15.7 MA DYWIDAG Strand Tendons using the cantilever method. Both Type 1S 21.8 and 1S 28.6 pre-grouted DYWIDAG Tendons were used for transverse post-tensioning.