Comparing response of SDF systems to near-fault and far-fault earthquake motions in the context of spectral regions

In spite of important differences in structural response to near-fault and far-fault ground motions, this paper aims at extending well-known concepts and results, based on elastic and inelastic response spectra for far-fault motions, to near-fault motions. Compared are certain aspects of the response of elastic and inelastic SDF systems to the two types of motions in the context of the acceleration-, velocity-, and displacement-sensitive regions of the response spectrum, leading to the following conclusions. (1) The velocity-sensitive region for near-fault motions is much narrower, and the acceleration-sensitive and displacement-sensitive regions are much wider, compared to far-fault motions; the narrower velocity-sensitive region is shifted to longer periods. (2) Although, for the same ductility factor, near-fault ground motions impose a larger strength demand than far-fault motions-both demands expressed as a fraction of their respective elastic demands-the strength reduction factors R-y for the two types of motions are similar over corresponding spectral regions. (3) Similarly, the ratio u(m)/u(0) of deformations of inelastic and elastic systems are similar for the two types of motions over corresponding spectral regions. (4) Design equations for R-y (and for u(m)/u(0)) should explicitly recognize spectral regions so that the same equations apply to various classes of ground motions as long as the appropriate values of T-a T-b and T-c are used. (5) The Veletsos-Newmark design equations with T-a = 0.04 s, T-b = 0.35 s, and T-c = 0.79 s are equally valid for the fault-normal component of near-fault ground motions. Copyright (C) 2001 John Wiley & Sons, Ltd.