| Large wall-type reinforced concrete structures can be visualized as assemblies of membrane elements. Their behaviors can be predicted if the behaviors of the membrane elements are known. Cracking in reinforced concrete transforms it from a linear, isotropic material into a non-linear, orthotropic material. According to recent tests on reinforced concrete membrane elements (or panels) at the University of Houston, the post-yield behavior of such panels can be rationally predicted only if the Poisson effect (mutual effect of the two normal strains) are taken into account. This Poisson effect is characterized by two Hsu/Zhu ratios. According to the test results of 12 specimens, the "Hsu/Zhu ratio nu21" (tensile strain caused by perpendicular compressive strain) was found to be about 1.9 in the post-yield range, and the "Hsu/Zhu ratio nu 21" (compressive strain caused by perpendicular tensile strain) may be negative and is negligible.;A new softened-membrane model is proposed to take into account the two Hsu/Zhu ratios. The existence of the descending branches in load-deformation curves of reinforced concrete membrane elements under pure shear has been a puzzle for many years. The Hsu/Zhu ratios and the new softened-membrane model will provide not only a rational explanation but also a means for their predictions.;This dissertation also presents a new rational shear modulus for the fixed-angle softened-truss model and the softened-membrane model based on the smeared-crack concept. This rational, yet very simple, modulus not only greatly simplifies the solution of these two models but also improves their accuracy. Moreover, this new shear modulus can be used widely to replace the many complicated empirical constitutive laws for shear in cracked concrete, as employed in various nonlinear analyses of reinforced concrete structures. A notable example is the finite element analysis. |
