Behavior and Analysis of 100 MPa Concrete Membrane Elements

Fourteen full-size reinforced panels (membrane elements) made of 100 MPa high-strength concrete were biaxially tested in the universal panel tester at the University of Houston. A new servocontrol system, newly fitted to the panel tester, allowed us to conduct strain-control tests and, for the first time, to correctly measure the three-dimensional (3-D) stress-strain curves of panels and the descending branches of the compressive stress-strain curves of concrete. The 3-D stress-strain curves provided new insights into the failure processes, and thus revealed the true stress-strain relationships of concrete and steel that were misinterpreted in the past using the conventional two-dimensional (2-D) stress-strain curves. Five 100 MPa concrete panels in this research were subjected to biaxial tension-compression. By comparing the behavior of these panels with those of 42 and 65 MPa tested previously, the writers were able to evaluate the effect of concrete strength on the constitutive laws of concrete in compression. Because the softening coefficient in this law was found to be inversely proportional to the square root of concrete strength $\left({\mathit{f}}_{\mathit{c}}^{\prime }\right)\text{,}$ those constitutive laws obtained previously for normal strength concrete can now be generalized to include concrete strengths up to 100 MPa. The remaining nine test panels were subjected to pure shear. The load-deformation behavior of these panels was correctly predicted by both the rotating-angle softened-truss model (RA-STM) and the fixed-angle softened-truss model (FA-STM). The range of applicability of these two models previously obtained for normal strength concrete were found to be valid for high-strength concrete as well. The failure modes of high-strength concrete panels were also predicted by a theoretical failure modes diagram.