A Modified Response Spectrum Analysis Procedure To Determine Nonlinear Seismic Demands of High-Rise Buildings With Shear Walls

Abstract eng:
The standard Response Spectrum Analysis (RSA) procedure prescribed in various codes and design guidelines is commonly used by practicing engineers to determine seismic demands for structural design purpose. In this procedure the elastic force demands of all significant vibration modes are first combined and then reduced by a response modification factor (R) to get the inelastic design demands. Recent studies, however, have shown that this standard RSA procedure significantly underestimates the true inelastic demands of high-rise buildings as higher vibration modes tend to remain elastic (or undergo very little nonlinearity), and therefore it may not be appropriate to reduce their demand contribution by the same factor. In this study, a modified RSA procedure based on equivalent linearization concept is presented. The underlying assumptions are that nonlinear seismic demands can be approximately obtained by summing up individual modal responses, and that the responses of each individual vibration mode can be approximately represented by those of an equivalent linear SDF system. Using three high-rise buildings with reinforced concrete shear walls (20-, 33- and 44-story high), the accuracy of this procedure and the standard RSA procedure are examined. In this examination, the inelastic demands computed by the Nonlinear Response History Analysis (NLRHA) procedure are used as benchmark. The modified RSA procedure is found to provide a reasonable degree of accuracy for all case study buildings under different input ground motions.

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