CONSTITUTIVE LAWS OF CONCRETE IN TENSION AND REINFORCING BARS STIFFENED BY CONCRETE

Constitutive laws of concrete in tension and reinforcing bars stiffene d by concrete are required in the formulation of the softened truss mo del theory for predicting the in-plane behavior of reinforced concrete membrane elements. These two constitutive laws were determined by tes ting 17 reinforced concrete panels under pure tension in a universal p anel tester. The test panels were reinforced by deformed steel bars in the direction of the applied tensile stresses. Based on the test resu lts, analytical expressions were derived for these two stress-strain r elationships. It was shown that the concrete develops substantial tens ile stresses even after extensive cracking. Expressions are given rela ting the average principal tensile stress in the concrete to the avera ge principal tensile strain of the panel. The stress-strain curve of a mild steel bar tested in a bare condition exhibits a long plateau aft er yielding. However, the average stress-strain curve of mild steel ba rs embedded in concrete does not show such a yield plateau. The ''appa rent yield stress'' is lower than the yield stress of a bare bar. Expr essions are proposed to relate the average tensile stress to the avera ge tensile strain of the steel.