Response of suspension bridges to travelling earthquake excitations: Part II-lateral response

The lateral response of suspension bridges to travelling earthquake excitations is investigated in the time and frequency domains. The ground motion inputs at one support are assumed to propagate, with different speeds, such that they hit the other supporting points of the structure with no change of shape (non-dispersive waves). It is assumed that the vibration of the center span can be treated separately from that of the side spans; furthermore, both the piers and towers are assumed to be relatively rigid in the lateral direction. A finite element dynamic analysis is utilized to investigate the lateral earthquake response. The response of the Golden Gate Bridge to ground motions recorded during the 1979 Imperial Valley earthquake is studied. It was found that the transmission time can have a significant effect on the response, that a relatively large number of modes is necessary to obtain a reasonable representation of the response, that uniform ground motion is not a good assumption, and that the additional cable tension induced by the lateral excitation is very small in comparison with the dead-load value; however, the induced displacements and flexural stresses can be significant live load conditions.