Nonlinear dynamic seismic analysis of a high-rise concrete core wall building with podiums using the beam-truss model

This paper describes the nonlinear dynamic seismic response of a thirty-six-story reinforced concrete U-shaped coupled core wall building using the Beam-Truss Model for the vertical elements of the lateral force-resisting system. The case study has three basements, eight podiums, and twenty-five tower levels, with eccentricities on every floor. Eleven nonlinear response-history analyses using bi-directional horizontal input ground motion were performed. The mean results show 56% larger shear forces at the core than those estimated by the code. There were significant differences in the in-plane shear forces at segments of the core wall; the largest was in the cantilever direction at the podiums, with cases in which one of the U-shaped walls resisted 100% of the shear force. Yielding of the vertical reinforcing occurred up to 59% of the height of the building. In certain analyses, the effect of the higher modes resulted in larger vertical tensile strains at the upper stories than at the top of the basements. The performance was acceptable when compared to the recommended limits included in the guidelines. However, when assessed through a strain-based approach found in the literature, the criteria of immediate occupancy was not met, as the strain limit for large diagonal shear cracks was exceeded. Modal analyses of the post-earthquake structure resulted in elongation of the periods associated with the first and higher modes by more than 250%.