Experimental investigation of deformation characteristics of concrete under cyclic biaxial compression with constant confined stress

An experimental research program was carried out with the aim of investigating the deformation characteristics of normal strength concrete under multistage cyclic biaxial compression with constant confined stress. A biaxial compressive test equipment based on the stress-controller close-loop system of MTS was reconstructed and used in the test. The results of fatigue tests were presented in the form of the diagrams of cyclic stress-strain curves which were recorded in the progress of tests. The deformation characteristics including the development of longitudinal and transverse fatigue strains, the secondary creep rate under the states of constant-amplitude and variable-amplitude cyclic compressive loads,and deformation modulus of concrete in terms of cyclic number, were drawn from the analysis of experimental results. In addition, An ultrasonic pulse velocity method was used to measure the damage growth during cyclic loading of concrete, and which results implied the progress of failure of concrete under biaxial cyclic compressive loads with constant confined stress. The microcosmic destructive mechanism of concrete under the present stress states was analyzed as well. The experimental results showed that the failure mode of compression fatigue of concrete was correlated with the magnitude of confined stress, while the development of fatigue strain conformed to the laws of three-stages. Furthermore, the rate of strain in second stage had also a perfect correlation with the fatigue life of concrete.