Performance of Modified Response Spectrum Analysis (MRSA) Procedures for Predicting the Seismic Demands of High Rise Buildings

Abstract

The development of earthquake analysis procedures has been the subject of several studies over the years. The design of structural systems to resist lateral forces has evolved significantly. Increasing computational power has contributed significantly to improving the accuracy of simulations. Several research studies found that Standard RSA under-estimates the elastic seismic forces of high-rise buildings by reduction of seismic forces of all vibration modes by the same Response modification factor R. However, higher modes remain elastic or experience very little nonlinearity. Recent studies proposed modified versions of RSA to overcome discrepancies of standard RSA. In this research study, the performance of the proposed modified response spectrum analysis (MRSA) procedures (MRSA (E.L), MRSA (H.E), and MRSA (H.I)) is evaluated using three case study high-rise buildings (20, 33, and 44-story) under different intensities of ground motions. Nonlinear response history analysis (NLRHA) has been used to assess the effectiveness of these MRSA procedures. To understand the composition of MRSA procedures, Uncoupled Modal Response History Analysis (UMRHA) is used. In UMRHA, the nonlinear response of every significant vibration mode is independently determined and combined to get the overall nonlinear response of buildings. The result indicates that UMRHA captures all the responses very well. MRSA (E.L) predicts all seismic responses perfectly, and it follows the same pattern as the UMRHA since it is independent of the numerical incorporation of nonlinearity by Response Modification Factors. In MRSA(HE) and MRSA (H.I), Up to 18 to 20 stories can be used to calculate displacements but underestimate above 20 stories. For story shear and overturning moments, both of these remain conservative. The UMRHA has provided several key insights about the relative contribution of all significant vibration modes.