Using a Lumped Mass, Nonuniform Stiffness Beam Model to Obtain the Interstory Drift Spectra

Abstract

The drift spectrum has recently been introduced as a new measure for estimating the interstory drift demands in buildings under near-field earthquakes. In this study, a method for estimating the drift demands in buildings with different structural systems is presented. Unlike previous studies that use a continuous beam, a stick model is employed to estimate the seismic-induced interstory drift demands. The proposed method can overcome the deficiencies of the previously introduced models. It considers the effect of heightwise stiffness reduction on drift demands, which is shown to be very important, and makes it possible to construct the drift spectra for low and medium-rise as well as high-rise buildings. The suggested method is simple because it uses the well-established modal analysis technique of lumped mass beams. The drift spectra for shear building models are constructed using near-field strong ground motions. The effects of the ratio of the lateral stiffness of top story to that of first story, heightwise variation of structural stiffness, number of stories, damping ratios, and higher modes on drift demands are investigated. A method is presented for using these spectra in estimating the drift demands in moment resisting frame structures, and the accuracy of the method is verified using a number of building models.