Strictly based on experimental evidence, a non-linear material model is presented for concrete
subjected to membrane stresses. The model assumes a smeared rotating crack approach, tension
stiffening, stress degrading effect for concrete parallel to the crack direction, and shear
retention of concrete on the crack surface. In addition, the concrete model considers the
enhancement in stiffness and strength of concrete under bi-axial compression. A NLFEA
computer code was developed by incorporating the model into standard finite element
formulations. The code applies to the analysis of rc plates and membranes. Colnparison with
experimental results indicates the efficiency of the material model in predicting the postcracking
response of reinforced concrete even with lower-order type of elements.