A remarkable new arch bridge connects the islands of Kashirajima and Kakuijima

Kashirajima Bridge in the Seto Inland Sea, Okayama Prefecture in Japan

The Kashirajima Bridge will be Japan's largest composite arch bridge. It has main girders with few steel components and an arch span of 218.0 m. The bridge is distinguished by the use of an arch configuration that is extremely flat for a large arch bridge (arch rise ratio 1/8).

For the erection of the bridge, in order to close the arch ribs as quickly as possible, a combination of the forestay cantilever and the MELAN arch method (see text) was used,with 60% of the main span established in a preliminary phase by a twin hollow box section girder made of structural steel (figure on top). The composite arch section was subsequently completed using high-strength concrete (figure on the bottom).

Since Kashirajima Bridge is an ocean bridge, the MELAN arch members, total length 130.4 m, were installed in a single lift using a 1,300-ton floating crane.
DYWIDAG post-tensioning tendons and anchorages were used for the temporary stay cables.

The MELAN arch bridge building method

The MELAN arch bridge building method is often used for arch bridges, where no intermediate supports can be placed in midspan, and particularly for flat arches which can no more be erected economically using the free cantilever method only. In this method, the arch configuration is first established by a preliminary girder made of structural steel (truss girder or hollow box section, as in the present case).
This girder is subsequently "jacketed" by the definite concrete section of the arch and will thus be integrated into the composite arch structure. Once the arch completed, the vertical members and the superstructure of the bridge are erected.


Construction phase prior to
erecting the superstructure

Placing of the MELAN arch
section, length 130.4 m