Experimental investigation of concrete under multiaxial extension: loading path dependent stress-strain behaviour

This paper presents a methodology for experimental detection of changes in mechanical properties of concrete under multiaxial compression and the findings of an experimental investigation of concrete under triaxial extension. Series of 100 mm cubic specimens with different moisture content were tested under cyclic loading to the extension meridian of the strength envelope (Lode angle theta = -pi/6) at several levels of hydrostatic confinement. The tests were performed by using two types of deviatoric loading: (i) conventional triaxial extension and (ii) reduced triaxial extension; and two different cycling sequences, by progressively increasing or decreasing the hydrostatic confinement. In addition to general stress-strains relationships recorded during the loading cycles, the stress-strain behaviour of the material was investigated by measuring the stresses during short periods of constant strains and by stress-probing in the three principal stress directions, both applied at various stress states during the tests. The results provide evidence for the influence of loading history on the stress-strain and creep-relaxation behaviour of the material as well as a link between the global (macroscopic) stress-strain behaviour of the specimens and the development of damage (or strain localization) within the fabric of the material.