Shake table experimental study of curved bridges with consideration of girder-to-girder collision

摘要

It is well-known that curved bridges are vulnerable to girder unseating during strong earthquakes. This is mainly attributed to its irregular geometry and seismic pounding. In this paper, a shake table experiment was designed and conducted on a 1/25-scale model to investigate the influence of collision between adjacent girders on the seismic response of curved bridges. For this purpose, two curved bridges with an expansion joint in-between were taken as the engineering background. Three historical records including a near-fault pulse-like record, a nonpulse-like record and a far-field ground motion were used to excite the test model. The seismic responses of the tested curved bridges were discussed in detail. Impact forces were measured by three load cells installed at the expansion gap joint. To begin with, the model was excited by the near-field pulse-like record in a variety of input directions without seismic collision to identify the most unfavorable input angle of the ground motions. It was found that for the test model, the secant direction of the adjacent two piers of the single-span segment is the most unfavorable input angle for seismic excitations. It was also found that the collision frequently occurred at the corners of the girders and was non-uniform along the contact surface. In addition, the girder-to-girder collision could induce significantly large in-plane rotation of the adjacent bridges, which could substantially increase the global displacement demands of the bridges. Furthermore, the maximum total impact forces increased with the gap size from 1 mm to 2 mm and then decreased with the gap size from 2 mm to 4 mm. However, the maximum in-plane rotation decreased with the gap size from 1 mm to 4 mm regardless of the input motions. Compared with the non-pulse-like near-fault motions, the pulse-like near-fault motions can result in higher in-plane rotation and force demands due to their velocity pulses and hence are more detrimental to curved bridges.