Large wall-type reinforced concrete structures can be visualized as assemblies of membrane elements. The behavior of a whole structure may thus be predicted if the collective behavior of all its component membrane elements (or panels) can be determined. Fourteen full-size reinforced panels with 100 MPa concrete were tested to determine the constitutive laws of membrane elements with high strength concrete. Two sets of constitutive laws of concrete and steel bars are established. The first set of constitutive laws is established for rotating-angle softened-truss model, in which the stress-strain relationships of concrete are developed in the principal directions of cracked concrete. The second set of constitutive laws is established for fixed-angle softened-truss model, in which the stress-strain relationships of concrete are developed in the principal directions of the applied stresses.
Equations proposed previously for the average stress-strain relationship of normal strength concrete in tension and that of steel bars embedded in normal strength concrete were found to be applicable to high strength concrete. The compressive softening coefficient, however, was found to be inversely proportional to the square root of the concrete strength √ f 'c. As a result, the maximum shear strength of reinforced concrete members and the balanced shear steel ratio were found to be proportional to √ f 'c.
The behavior of test panels subjected to pure shear was accurately predicted by both the rotating-angle softened-truss model and the fixed-angle softened-truss model. However, the assumption of crack angle in the rotating-angle model limits its applicability to a range of 0.4 < η < 2.5, where η is the ratio of steel yield forces in the two directions. The fixed-angle model is more powerful, with a range of applicability of 0.2 < η < 5.
The panel tests were carried out in a strain-control procedure using a servo control system. The strain-control tests allowed us to correctly measure the, for the fist time, the Poisson ratios of cracked reinforced concrete. The Poisson ratios can be incorporated into the finite element analysis to predict the behavior of reinforced concrete structures.