Response of Mortar and Concrete to Biaxial Compression

A series of cubical mortar specimens was tested to failure under monotonically increasing proportional biaxial loading, using two types of boundary constraints. The resulting stress-strain curves and strength data were evaluated in order to establish a unified formulation of the material behavior for use in analysis. It was deduced that a unified engineering description of the constitutive behavior covering all applied stress ratios is possible by use of octahedral stress-strain relations. The nonlinearities can be represented by the bulk and shear moduli expressed as functions of stress level. Strength data indicate that constrained boundary displacements of the specimens not only increase the uniaxial strength, but also give relatively higher biaxial strength values. Strain ratios and strain values at failure are investigated in order to shed light on the post-failure behavior of the material.