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In Japan, expressway bridges are aging and deteriorating because of increases in traffic volume and loading, harsh environments and other factors. Therefore, a renewal plan for bridges was drafted to address this issue in 2015. The main works include replacing reinforced concrete (RC) slabs of steel girder bridges with precast prestressed concrete (PC) slabs. In renewal plan for RC slab, if the severe deterioration occurs in the RC slab, that will be renewed to high durability precast PC slab. In the design of the new PC slab, the structure and material is determined in consideration of the degradation factors of the old RC slab. The new PC slab is necessary to have sufficient durability against the environmental action during design service life and to have sufficient safety against automobile load. In this paper, the design method and structure of the new PC slab are described.

More than fifty years have passed since the first roadway opened for service in Japan's network of intercity expressways managed by expressway companies. As with the roadways, the expressway bridges are aging and deteriorating because of increases in traffic volume and loading, harsh environments and other factors. Therefore, a renewal plan for bridges was drafted to address this issue. The renewal plan will implement large-scale renewal, reinforcement and repair of bridges which cannot satisfy bridge performance requirements over the long term with the usual small-scale reinforcement and repair alone because of advanced deterioration caused by such factors as salt damage and fatigue due to traffic loading. The main works include replacing reinforced concrete (RC) slabs of steel girder bridges with precast prestressed concrete (PC) slabs, replacing salt-damaged and deteriorated concrete surfaces with sound concrete structures, reinforcing bridges containing corroded prestressing steel and repairing fatigue cracks in steel structures. In sustainable renewal plan for RC slab of steel girder bridges, if the severe deterioration occurs in the RC slab, that will be renewed to high durability precast PC slab. In the design of the new PC slab, the structure and material is determined in consideration of the degradation factors of the old RC slab. Also, materials of the new PC slab are demanded the high durability against salt damage. The schedule of works will take around 15 years to implement. The cost is 1,640 billion yen (about 13 billion US$).