Evaluation of Coefficient and Equivalent Linearization Method of FEMA-440 for Soil-Structure Systems

Abstract eng:
In recent years, Nonlinear Static Procedures (NSPs) have been attracted numerous researchers. The purpose of developing these methods is to predict the nonlinear demands of structures in a simple way with an acceptable accuracy. The whole MDOF structure converts to an equivalent nonlinear SDOF via pushover analysis and the nonlinear displacement of this SDOF system approximates approximately the nonlinear displacement of the whole structure. In order to find the nonlinear displacement of SDOF system varied methods are proposed in which Coefficient Method and Equivalent Linearization Method are the most applicable ones. It could be referred to FEMA-273, FEMA-356, and ATC-40 as the pioneer documents on this issue. It was also presented in FEMA-450 in design procedures. However, the aforementioned procedures were modified in FEMA-440 by analyzing a fixed base SDOF through 20 ground motions recorded at each site class categorized by FEMA-450. Moreover, the effect of Soil Structure Interaction on nonlinear demands in NSPs was discussed more elaborately than previous documents. As it was mentioned, since all the optimizations of FEMA-440 were performed for a SDOF model fixed at its base, its accuracy for soil structure system should be evaluated. In this study all the analysis were done in response spectra format for key influential non-dimensional parameters in soil-structure systems in order to make the result more comprehensive and applicable for wide ranges of ordinary structures and soil conditions.

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