Biaxial strees–strain relationships for concrete

On the basis of experimental results reported more fully elsewhere, a stress-strain relationship is proposed for plain concrete that is applicable to all combinations of biaxial tension and compression. The proposed equation accounts for both non-linear and orthotropic behaviour of concrete. Also based on experimental results, a biaxial ultimate strength criterion is proposed for concrete in the form of a failure stress envelope. The proposed equations are given in a form such that they may be incorporated readily in plane-stress analysis of reinforced concrete using the finite-element approach.