The modified and extended upper-bound (UB) pushover method for the multi-mode pushover analysis of unsymmetric-plan tall buildings

Abstract

Upper-bound (UB) pushover analysis method, which was proposed to consider the effect of higher modes for two-dimensional (2D) tall building frames, underestimates the seismic demands at the lower storeys. In this study, the limitation of the method is resolved by combining the seismic demands resulting from the upper-bound pushover method and a conventional pushover analysis that the latter controls the seismic demands at the lower storeys. Furthermore, the main aim of this study is the extension of the upper-bound pushover analysis method to unsymmetric-plan tall buildings to take torsional effects into account. The extension is carried out based on the use of upper-bound lateral forces with different patterns for various unsymmetric-plan tall buildings. The upper-bound of the contribution ratio of higher modes is considered in computing the upper-bound lateral forces. The results elucidate that the extended method can predict to a reasonable accuracy the inelastic seismic demands of unsymmetic-plan tall buildings.