Miyako-Irabu Bridge, a new reference in Japan
FKK (Kyokuto Kogen Concrete Shinko Co., Ltd.),
licensee of Freyssinet in Japan for post-tensioning, supplied the post-tensioning
for the marine bridge connecting Miyako Island and Irabu Island of the
Okinawa archipelago, located in the southernmost point of the country.
The bridge is 3,540 meters in length:
- the central part of the bridge (420 meters) comprising the navigation channel is made of a steel structure with three continuous spans;
- the 2,185 meters on the Miyako Island side is made of 32 continuous spans of prestressed concrete box- bridge;
- the 925 meters on the Irabu Island side is made of 14 continuous spans of prestressed concrete box- girder bridge.
The construction started in March 2006 and the bridge has been open since January 2015.
This area is often hit by typhoons in the summer; the strongest typhoon recorded reached wind speeds of 307 km/h. The bridge is also subjected to strong seasonal winds in the winter, resulting in a sea salt deposit. Therefore, due to this adverse environment, extreme wind resistant structures were required.
The pre-stressed concrete bridges were constructed using the balanced cantilever method using 977 precast concrete segments (produced in a precast yard in Miyako Island) placed in cantilevers sequentially connected. The post-tensioning anchorages were supplied by FKK, the longest-standing Freyssinet licensee in the world (since 1952).
