Suspension Bridge Response to Multiple-Support Excitations

Abstract

The earthquake-induced vertical response of suspension bridges when subjected to, correlated or uncorrelated, multiple-support excitations is analyzed by means of random vibration theory. Appropriate ground motions describing the basic inputs to such structures are defined through finite Fourier transforms of existing recorded ground displacements at locations within distances similar to the spans of such structures. Spectral correlation analysis of the multiple-support excitations are estimated via these Fourier transforms. It is found that studies of earthquake-induced vertical motion of suspension bridges need to take into account the influences of ground excitations in the longitudinal directions of such bridges. An example is presented in which the response of an existing bridge (in a seismically active area) to earthquake ground motions with characteristics significantly different at the supports is examined. It is observed that the participation of higher modes in the total response is essential to reliably assess the seismic behavior of such structures and that the response values associated with correlated multiple-support excitations are significantly different from those obtained through the uncorrelated case.