Shear Strength of Reinforced Concrete Members Subjected to Monotonic and Cyclic Loads

Abstract

The shear capacity of reinforced concrete members subjected to monotonic loads was investigated and used as the basis to formulate an expression to calculate the strength of members subjected to load reversals. The monotonic shear capacity of slender beams, deep beams, walls, and columns was calculated by superposition of components related to arch-action, trussaction, friction, and from a contribution of the uncracked compression zone, which is related to the tensile strength of concrete. A procedure to calculate the shear strength of members in the transition phase from deep to slender members was formulated, so that the proposed expression can be used for all geometries considered. The shear strength of members with and without web reinforcement was analyzed. The proposed model was calibrated using an extensive database of test results, and was found to give good results compared to other analysis models in an n-fold cross validation. The resistance to lateral load reversals was investigated for two failure modes: failure due to degradation of the flexural strength, and failure due to degradation of the shear strength. The degradation of flexural strength is expressed in terms of a linear slope derived from the displacement and load at yielding of the tensile reinforcement to the displacement at 80 percent of the yield load. Shear failure was defined by yielding of the transverse reinforcement. The degradation of shear strength was found to be non-linear with respect to the limiting displacement, and is formulated as a reduction factor for the initial shear strength. Degradation functions for the decrease in strength of the contributing arch and compression zone components, and for the truss mechanism are presented. The following key conclusions were drawn from this study: 1. The monotonic shear capacity can be modeled by the proposed superposition of contributing components for member geometries ranging from squat to deep members. Simply superimposing the individual components, however, does not reflect the actual member behavior. Functions transitioning between squat and slender members, as well as between reinforced members and members without web reinforcement, are necessary to model the member behavior accurately. 2. In the proposed model, the friction component is used to control the so-called "size effect." It was found that the "size effect" is not only an effect of the section depth, but is also influenced by the compressive strength of concrete, the tensile reinforcement ratio, and the average shear stress. ii 3. The shear strength degradation under cyclic lateral loads was found to be due to a reduction of the components related to friction and the compression zone, and to a reduction of the truss mechanism. 4. The shear analysis according to the proposed model gave more accurate results than the other models considered in the study at hand. Moreover, with the exception of the approach proposed by Watanabe, compared to other methods, it was the only model applicable to a wide range of member configurations.