Title: Softened Membrane Model for Reinforced Concrete Elements in Shear

Author(s): Thomas T. C. Hsu and Ronnie R. H. Zhu

Publication: Structural Journal

Volume: 99

Issue: 4

Appears on pages(s): 460-469

Keywords: load; reinforced concrete; shear; strain; stress

DOI: 10.14359/12115

Date: 7/1/2002

Abstract:
Biaxial stress and strain conditions are produced in reinforced concrete elements subjected to shear. Current shear theories, which neglect the Poisson effect (mutual effects of the two normal strains), can reasonably predict the ascending branches of the response curves, but give descending branches that are either irrational or inaccurate. This paper presents a new theory, the softened-membrane model, that can confidently predict the entire behavioral history including both the prepeak and the postpeak behavior. In this general theory, the postpeak behavior is rationally predicted by taking into account the stresses and strains caused by Poisson effect. The Poisson effect is characterized by two Hsu/Zhu ratios, defined as “the Poisson’s ratios of cracked reinforced concrete based on the smeared-crack concept.” In the smeared-crack concept, cracked reinforced concrete is treated as a continuous material, and the constitutive laws of concrete and steel bars are expressed in terms of smeared (average) stresses and smeared (average) strains. As a result, the Hsu/Zhu ratios are the same for both the smeared concrete and the smeared steel bars. The experiments to measure the two Hsu/Zhu ratios are reported in a companion paper.