Accuracy of RSA Design Demands for Multi-Tower Buildings

Response spectrum analysis (RSA) procedure commonly used in design practice has been found to underestimate design forces in tall buildings. This study aims to check the accuracy of the RSA procedure when applied to multi-tower buildings sharing a common podium. Two hypothetical multi-tower buildings, the first consists of two towers with the same height (building SH), and the second consists of two towers with the different height (building DH), were designed for Chiang Mai site of Thailand using the conventional RSA procedure, and then the nonlinear response history analysis (NLRHA) is carried out. Results from NLRHA, which is the most accurate method, were used as reference values to evaluate the accuracy of RSA procedure. The results show that seismic shear demand from nonlinear analysis is about 3 times larger than the demand obtained from the RSA procedure. This could lead to shear failure in the shear walls designed by RSA procedure. Since the elastic method is preferred in practice, 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. It is found that MRSA provides good estimates of shear force in vertical elements. MRSA can significantly enhance the design of tall buildings by avoiding brittle shear failure.