Abstract
The multi-span suspension bridge, a novel bridge system, has emerged as an economically viable alternative for sea-crossing bridges with extensive spans. However, as bridge length increases, the complex correlation between support excitation becomes apparent due to the coherency effect in the underlying soil and the seismic wave-passage effect, termed Multi-Support Excitation (MSE). This study focuses on the seismic responses of Multi-span Suspension Bridge (MSB) under MSE, taking into account incoherence and wave-passage effects. The study conducts a time history analysis of “Cheon-Sa Bridge” to investigate the responses of girder and pylons under three different types of homogenous soil conditions: soft, medium, and firm, with three different apparent wave velocities of 600 m/s, 900 m/s, and 1200 m/s. The responses obtained for different MSE cases are compared with a uniform seismic excitation of recorded earthquake ground motion of El-Centro 1940, Imperial Valley: 180 deg. Results show that MSE significantly affects the longitudinal and vertical responses of MSB. The girder exhibits 3.3 times higher deflections under soft and medium soil MSE cases. The MSE cases significantly increase the girder axial force by about 6 times that of the uniform excitation case. The side pylons exhibit a 30% – 38% increase in transverse responses and approximately 10–12 times higher longitudinal responses. It is concluded that the local site conditions and corresponding acceleration spectral density of bedrock motion significantly influence the response of MSB. Merely considering the wave-passage effect may underestimate the actual response.