Biaxial Stress-Strain Relations for Concrete

On the basis of an extensive experimental investigation reported more fully elsewhere, an analytical form of stress-strain relationship for plain concrete in biaxial compression is proposed. This plane-stress orthotropic constitutive relationship accounts for the influence of microcrack confinement as well as Poison's ratio. Other equations found in the literature are shown to be special cases of the one proposed. Also based on experimental results, a simple equation is offered which accounts for the increase in compressive strength of plain concrete when biaxial compressive stress is introduced. Both the biaxial stress-strain equation and the strength equation are shown to give good agreement with the experimental results obtained by the writers as well as by others. Finally, a constitutive law, stated in matrix terms, is given for concrete in biaxial plane stress. This relation is suitable for use in the finite element analysis of reinforced or presstressed concrete.