Behavior of Concrete under Multiaxial Stress States

Differences in the observed behavior of concrete under multiaxial stress states can be ascribed to either different materials or different test methods. In order to isolate the effects of these two variables, seven institutions cooperated in a test program in which specimens of indentical material were subjected to variety of biaxial and triaxial stress states common to all participants. Specimen loading conditions ranged from flexible, uniformly-stressed membranes through various intermediate conditions to rigid, rough steel plates providing uniform surface displacements. Stress-strain relations obtained are presented and examined. They indicate that there are some systematic differences in results which depend on the test method used. The principal stress-strain relations from the tests are transformed into octahedral space, and the material response is expressed in terms of variable bulk and shear moduli. A coupling effect relating volume change to stress deviation was also observed. Moduli from the biaxial and triaxial tests are compared to explore the range of validity of a inified formulation.