Compressive behavior of high-strength high-performance concrete under biaxial loading

Components of most concrete structural systems, such as slabs, long span thin shells, containment vessels and protective structures are stressed in multiaxial states of stress. This study explores the behavior of high strength high performance concrete under biaxial loading in comparison to uniaxial loading conditions, and to propose a modified Elastic Modulus expression for concretes under biaxial loading for cylinder compressive strengths above 12,000 psi (82 MPa). In excess of 100 high-strength cube specimens in several series were tested to failure under uniaxial and biaxial compression. Ratios of the minor to major principal stresses (sigma(2)/sigma(1)) were selected as a major test variable. From the test results, it is shown that confinement stress in the minor principal direction has a pronounced effect on the strength and deformational behavior in the principal direction. Both the stifffness and ultimate strength of the concrete increased to a value of approximately 30 percent. Crack development in the tested specimens under biaxial compression progressed into asymptotic tensile splitting cracks along the sigma(2) direction. A mathematical model and an empirical equation were developed for the elastic modulus of concrete under biaxial loading as a result of these tests.