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Seismic demands on gravity-load columns of reinforced concrete shear wall buildings Bazargani, Poureya

Abstract

In shear wall buildings, walls serve as the seismic force resisting system while the gravity-load system consists of columns that are primarily designed to carry the weight of the building through frame action and are not detailed for seismic ductility. Design codes require the gravity-load system to be checked for deformation compatibility as the building deforms laterally. The process of checking the columns for adequate deformability still requires more work. In addition to flexural deformations, components such as shear strain and rotation of the foundation contribute significantly to lateral deformations in the wall plastic hinge zone. Shear strains in flexural shear walls are analytically shown to be a result of large vertical tensile strains in areas with inclined cracks. Based on this theory, a simple design-oriented method for estimating shear strain profile of flexural shear walls is formulated, the accuracy of which is verified against experimental results from works of other researchers. Rotation of shear wall foundations is studied through performing about 2000 Nonlinear Time-History Analysis (NTHA) considering the nonlinear interaction between the foundation and the underlying soil. Behaviour of shear walls accounting for foundation rotation is explained with emphasis on relative wall to foundation strengths. A simple method for obtaining the monotonic foundation moment-rotation response is formulated which is then used in a simple step-by-step method for estimating foundation rotation in a given shear wall building. Curvature demand on columns pushed to a given wall deformation profile is studied using a structural analysis algorithm specifically designed for the task. In the absence of wall shear strain or significant foundation rotation, column curvature demand is found to remain close to the wall maximum curvature. Wall shear strain and foundation rotation are found to cause severe increase to column curvature demand. In a parametric study on column curvature demand, parameters including wall length, column length, height of column plastic hinge zone, first storey height, fixity of the column at grade level, and the effect of members framing into the column are studied. Several simple expressions for estimating column curvature demand are derived that can be implemented in design.

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Attribution-NonCommercial-NoDerivs 2.5 Canada

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