Modified response spectrum analysis for computing seismic demands of multi-tower building sharing a common podium

Abstract

To design irregular tall buildings, performance-based design (PBD) approach, which requires nonlinear response history analysis (NLRHA), is the most accurate method. However, PBD approach is not always used in the current design practice because of its complexity, and as allowed in ASCE 7-16, design engineer can use code-based approach such as response spectrum analysis (RSA) procedure. This paper aims to investigate the accuracy of RSA procedure when applied to irregular tall buildings, and in particular for multi-tower buildings sharing a common podium. Also, a modified response spectrum analysis (MRSA) procedure previously proposed for computing shear demand in regular tall buildings, was tried to apply to irregular tall buildings in this study, since elastic method is preferred in practice. Two hypothetical multi-tower buildings were designed for Bangkok and Chiang Mai sites of Thailand using the conventional RSA procedure, and then NLRHA is carried out. The effect of different tower heights is also investigated by analyzing two buildings. The first has two towers with the same heights (building SH), while the second has two towers with different heights (building DH). The out-of-synchronization behavior of the two towers in building DH leads to significant increase of axial forces in the podium floors. It was found that RSA underestimates force demands, while MRSA provides good estimates of shear force in vertical and horizontal elements. MRSA can significantly enhance the design of tall buildings by avoiding brittle failure.