New Railway Viaduct Providing Superior Running Safety at Earthquake

Abstract

Summary The rigid-frame viaduct combined with a concrete track-bed of approximately a 10 m span has been popularly used in Japan. It suffered, however, severe damages in the Hyogo-ken Nanbu Earthquake in 1995. This rigid-frame viaduct needs a thick and wide concrete track-bed and becomes consequently a top-heavy and low natural frequency structure. The train running safety on viaduct during earthquake was studied using a vehicle/structure dynamic interaction analysis program. It is revealed that the train running safety is remarkably improved when the natural frequency of the viaduct becomes higher than 2Hz. To satisfy the requirement, it is essential to lighten the superstructure and stiffen the pier. A new viaduct structure was developed which is composed of a lightweight and environmentally friendly track, a lightweight prefabricated prestressed concrete girder that directly supports the single track and a rigid-frame reinforced concrete pier with steel brace and damper element. The lightweight and environmentally friendly track called the “floating ladder track” can reduce not only the weight by one-third compared with the conventional ballasted track but also the vibration on the track-bed by approximately 20dB. The weight of the superstructure is reduced by half using a lightweight hollow-section prestressed concrete tracksupporting girder. The stiffness of the pier is sufficiently increased using a steel brace with a small section and a steel panel-type damper. The seismic performance of the pier system was evaluated using a cyclic loading test.