RESPONSE ANALYSIS OF FLEXIBLE MDF SYSTEMS FOR MULTIPLE-SUPPORT SEISMIC EXCITATIONS

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. Copyright © 1990 John Wiley & Sons, Ltd