Constitutive Laws of Concrete in Tension and Reinforcing Bars Stiffened by Concrete

Constitutive laws of concrete in tension and reinforcing bars stiffened by concrete are required in the formulation of the softened truss model theory for predicting the in-plane behavior of reinforced concrete membrane elements. These two constitutive laws were determined by testing 17 reinforced concrete panels under pure tension in a universal panel tester. The test panels were reinforced by deformed steel bars in the direction of the applied tensile stresses. Based on the test results, analytical expressions were derived for these two stress-strain relationships. It was shown that the concrete develops substantial tensile stresses even after extensive cracking. Expressions are given relating the average principal tensile stress in the concrete to the average principal tensile strain of the panel. The stress-strain curve of a mild steel bar tested in a bare condition exhibits a long plateau after yielding. However, the average stress-strain curve of mild steel bars embedded in concrete does not show such a yield plateau. The ‘apparent yield stress’ is lower than the yield stress of a bare bar. Expressions are proposed to relate the average tensile stress to the average tensile strain of the steel.