Lateral Earthquake Response of Suspension Bridges

The lateral response of suspension bridges to multiple‐support seismic excitations is investigated. A frequency‐domain random‐vibration approach is utilized to take into account not only the differences in ground motion inputs, but also the correlation among the various input motions. The earthquake response of the Golden Gate Suspension Bridge, in San Francisco, California, is analyzed. The ground motion inputs were taken from an array of time histories recovered from the Imperial Valley, California, earthquake $\left(M_L?6.6\right)$ of October 15, 1979. Mean square displacements of both the cables and the suspended structures, as well as stresses in the later, are calculated. It was found that a relative large number of modes is necessary to obtain a reasonable representation of the response and that uniform ground motion over the entire span is not a good assumption for these long structures since it does not represent the worst possible conditions.