SIMPLIFIED DYNAMIC ANALYSIS OF THREE DIMENSIONAL SHEAR BUILDING ON ELASTIC FOUNDATION

Abstract

An efficient method is presented for the time-history analysis of seismically excited asymmetric shear buildings on flexible foundations. The governing equations are reduced to a set of integro-differential equations involving the interaction displacements alone with the degrees of freedom of the superstructure being eliminated through the use of modal analysis of the superstructure. The influence of shear wave velocities, building eccentricities and direction of earthquake on the response of the interaction system is investigated. In order to determine the maximum response of the interaction system by the response spectrum technique, approximate normal modes are derived. Accurate damping ratios for these approximate normal modes are obtained by matching the approximate normal mode solution with the rigorous solution. The modal maxima are combined using both the more widely used Square-Root-Sum-of-Squares (SRSS) method and the more recent Complete-Quadratic-Combination (CQC) method. The latter method is found to be more accurate for systems with closely spaced natural frequencies.