UBC Theses and Dissertations
Gravity-force resisting system flexural stiffness modifiers for seismic analysis of tall reinforced concrete shear wall buildings Granda Valencia, Camilo Sebastian
High-rise residential buildings are considered as one of the best solutions to the current lack of space in urban areas. In high-density cities in the Canadian Pacific Northwest, reinforced concrete shear wall structures are one of the main typologies used in tall buildings design. This type of building is composed of a seismic-force resisting system and a gravity-force resisting system. While the former system is designed to resist lateral loads, failure of the gravity-force system is recognized as one of the main causes of building collapse under earthquake demands. Accurate estimation of seismic demands in this system is critical to provide a safe design. The goal of this study is to obtain gravity system flexural stiffness modifiers to safely estimate their seismic demands following a linear-elastic analysis. The proposed flexural stiffness modifiers were derived from the moment-curvature analysis of members within a nonlinear 3D reinforced concrete shear wall structural analysis building model (with both seismic-force and gravity-force resisting systems modelled as nonlinear). These quantitative results for individual members are used to perform regression analyses to develop generalized equations to estimate the flexural stiffness modifiers in gravity-frame columns and slabs. Typical flexural stiffness modifiers range from 3-100% and 18-85%, for columns and slabs, respectively. In most of the cases, the results show that the gravity system bending moment demands of a linear-elastic analysis model with the proposed effective stiffness modifiers are consistent with the moment demands in an equivalent nonlinear model. The proposed recommendations provide appropriate estimates of seismic demands in the gravity-force system by means of realistic stiffness factors. Moreover, they support the implementation of the Simplified Analysis procedure for the gravity-system design of reinforced concrete shear wall buildings as outlined in the Canadian concrete standard (CSA A23.3-19 § 220.127.116.11) by practicing engineers.
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