Earthquake response analysis of multiple towers on a common podium

Abstract

In this study, one of the complex structural systems that requires extra caution during the design process, a tall building structure with multiple towers on a common podium, is analyzed considering effects of interaction between the towers due to connected podium floors. Nonlinear response history analysis is essential for performance-based design of tower structures. However, due to excessive computational demands of nonlinear analysis, using combined models for the multiple towers throughout design process is usually not viable. Therefore, to reduce analysis duration, analyzing separate single-tower models, using assumptions that typically neglect the interaction, is a common industry-standard approach. However, for more reliable response predictions, interaction of the towers with each other must be implemented in the analysis. In the current study, interaction effects of the podium floors are considered in the analyses, first using a simple approach of assigning either fixed or free end restraints at the continuous boundaries of the single-tower models. Responses of the single tower models are then compared with the response obtained using a combined model, which includes both of the towers as well as the common podium and basement floors. Results of various linear and nonlinear analysis methods are compared and the effects of interaction on the structural response are discussed. In addition to important response parameters associated with the tower structures, in-plane tensile and shear force distributions developing in the podium floors are also considered as critical design quantities. Results obtained demonstrate that response spectrum and linear response history analysis methods used for analyzing the combined model provide comparable internal tension and shear force resultants acting on the podium floors. The nonlinear analysis results obtained using the combined model for the tower response quantities are generally closer to those obtained from the single-tower model with free end restraints at the continuous boundaries. In both linear and nonlinear analyses, single-tower models with fixed end restraints overestimate the internal tension and shear forces at the podium floors, although to a reasonable extent.