There is now an urgent need to take measures against the deterioration of a number of steel bridges. The outright replacement of these bridges would incur enormous costs and involve train cancellation and other difficulties. To facilitate such work, the RTRI has developed a method to install plural floor slab pieces to create a composite structure. As this technique can be applied during intervals between trains, it cuts execution costs, improves the load-carrying capacity as a result of the composite structure, suppresses fatigue, prevents local corrosion directly beneath sleepers, extends the lifespan of the structure and reduces noise.

Figure 1 shows the flow of introducing a composite structure. Precast concrete slabs of about 3 m in length are placed on the floor after the track has been removed. They are then connected to the steel girder with their height adjusted, and a new track is laid on top. This method enables simple and quick execution without changing the rail level.

The top surface of existing girders may become uneven due to riveting or corrosion. To compensate for this unevenness, mortar is cast between the steel girder and the floor slabs. The RTRI has developed a method to connect the steel girder and floor slabs using two types of jig (Fig. 2) and confirmed through a loading test that sufficient strength is maintained between the floor slabs, the mortar and the bridge girder.

It was found that the increased dead load caused by installing floor slabs would adversely affect the girder and supports. The RTRI has confirmed, however, that this technology can be safely applied to steel bridges with spans of 40 m or less.

The RTRI plans to discuss the application of this technique to actual bridges.