Influence of ground motion characteristics and structural parameters on seismic responses of SDOF systems

Nonlinear response spectra are useful for estimating the response of structures to earthquake ground motions. The nonlinear response from the spectrum is only approximately equivalent to the global response of the actual structural system. However, the nonlinear spectra provide a simple method for estimating nonlinear response suitable for preliminary design or evaluation of a structure whose response is dominated by a single vibration mode.; This research focuses on the accuracy of nonlinear response spectra in representing the response of real structures under actual earthquake ground motions, and involves six main areas: (1) selection of filtered ground acceleration records for use in nonlinear response analyses, (2) investigation of the statistical properties of nonlinear spectral responses, (3) development of a method for estimating the nonlinear spectral response of structures using a smooth response spectrum typical of current seismic design provisions, (4) examination of the influence of the inherent damping model on nonlinear structural response, (5) assessment of nonlinear spectral responses of various types of structural systems with or without supplemental damping, and (6) development of smooth nonlinear response spectrum functions for use in evaluating structural systems.; The results of this study show: (1) ground acceleration records filtered to remove long period noise must have a filter effective cutoff period longer than structural period, elongated by nonlinear response, to yield accurate nonlinear response estimates; (2) the smooth median response, based on the assumption that nonlinear response follows the lognormal distribution, has advantages as the estimate of the likely response; (3) the smooth median nonlinear response spectra for systems with the yield strength determined from the smooth median pseudo acceleration spectrum for a ground motion set are similar to the smooth median response spectra for systems with the yield strength determined from the pseudo acceleration spectrum for the individual ground motions in the ground motion set; and (4) the inherent damping model used in most previous research, in which the damping coefficient is proportional to the initial frequency of a system, amplifies the damping ratio during nonlinear response, leading to a smaller nonlinear response, and new inherent damping model is proposed for nonlinear SDOF systems.; Regarding the effects of hysteretic behavior and supplemental damping, the results of this study show that: (1) the equal displacement rule for structures with periods in the range of 1 to 3 sec. is, in general, unconservative for systems with a small post yielding stiffness and a low lateral strength; (2) the ductility demands for the new self centering structural systems are much larger than those for conventional systems; and (3) the use of supplemental viscous damping can reduce ductility demands but for most of structures it will increase total acceleration demands.