Pinching Effect in Hysteretic loops of R/C Shear Elements

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Title: Pinching Effect in Hysteretic loops of R/C Shear Elements

Author(s): M. Y. Mansour, T. T. C. Hsu, and J. Y. lee

Publication: Special Publication

Volume: 205

Issue:

Appears on pages(s): 293-322

Keywords: analytical model; compatibility; concrete; constitutive laws; cyclic loading; equilibrium; hysteretic loops; membrane element; nonlinear analysis; pinching; reinforced concrete; reloading;

Date: 1/1/2002

Abstract:
The load-deformation response of R/C membrane elements (panels) subjected to reversed cyclic shear showed that the orientation of the steel bars with respect to the principal coordinate of the applied stresses has a strong effect on the pinching effect in the post-yield hysteretic loops. When the steel bars were oriented in the directions of the applied principal stresses, there was no pinching effect. When the steel bars were oriented at an angle of 45’ to the applied principal stresses, there was severe pinching effect. It was obvious that the pinching effect is caused by the orientation of the steel bars, rather than the bond slips between the steel bars and the concrete as surmised by many researchers. A non-linear analytical model capable of describing this pinching behavior is presented in this paper. The model is actually an extension of the fixed-angle softened truss model (FA-STM) proposed by Hsu and his colleagues for monotonic loading. The extension of FA-STM for application to reversed cyclic loading requires new constitutive models for concrete and steel in the unloading and reloading ranges. This rational theory satisfies Navier’s three principles of the mechanics of materials: equilibrium, compatibility and constitutive relationships of materials. The validity of this theory is illustrated by comparing the behavior of three panels with three different steel bar angles. The predicted cyclic behavior compared well with the experimental behavior, except in the descending branch.