BRIDGE OVER TROUBLED WATER.

Oshima Bridge connects the main island of Honshu with the smaller island of Oshima and spans a fast-running 850 m wide strait. The speed of the tide proved to be a major consideration in the construction of this bridge, the longest continuous truss bridge yet attempted in Japan. With a total length of 1,020 m, Oshima Bridge consists of a main bridge and two approach bridges, providing a roadway 7. 0 m wide for motor traffic plus a 1. 5 m pedestrian walkway. The main bridge comprises of a 325 m center span and two side spans of 200 m. It is the world's second longest bridge after the Astoria Bridge in the U. S. The conventional Japanese bridge erection method is to use temporary supports for insatlling side spans and the cantilever erection method for the center span. In the case of the Oshima Bridge, it would have been difficult to install temporary supports for erection of the side spans because of the fast current. Instead, the large prefabricated unit erection method was used, and the superstructures of the side-span portions were prefabrictaed in an assembly yard some 6 km from the erection site. The 2 000 t prefabricated side-span units were transported to the erection site by a large floating crane in the suspended position and erected during the short period of slack tide. This large prefabricated erection method is economic in time, cost, and relatively safe.