| Abstract: | Two practical approaches, response spectrum and time-history methods, are developed to evaluate the response of flexible multi-degree-of-freedom (MDF) systems, notably long-span bridges, to multiple-support seismic excitations. For practical convenience, ground motions within a group of adjacent supports on continuous soil or rock are assumed to be uniform and synchronized, while those of different groups are treated as non-uniform and uncorrelated. The response spectrum analysis is extended to include the cross-correlation of modal responses, which prove important when closely spaced modal frequencies exist. An example of the significance of multiple-support excitations is illustrated by application to a suspension bridge. Qualitatively comparable effects can be expected for other bridges of similar type or dimensions. |
