Experimental study and failure criterion analysis of plain concrete under combined compression-shear stress

To study the mechanical properties of plain concrete (with a standard compressive strength of 30 MPa) under combined compression-shear stress, the concrete was tested using material compression-shear hydraulic servo machine under various axial compression conditions. In the experimental study, the shear failure modes and shear load-displacement curves of concrete are obtained. The peak shear strength and residual strength of concrete are then extracted from the load-displacement curves. A total of three development stages of shear load-displacement curves are identified and mechanical characteristics at each stage are analyzed. The results show that the shear failure behavior of concrete under different axial compression is quite different, and as the increase of axial compression ratio, the traces of friction on shear plane get more evident and the concrete failure slag also increases. Based on the experiment data and regression analysis, it is observed that both the peak shear strength and residual strength of concrete increase linearly as the increase of axial compression ratio. From the residual strength analysis, the shear failure plane of plain concrete has a relatively stable friction coefficient of 1.46. According to octahedral stress space analysis and unified strength theory, the failure criterion curves of concrete under compression-shear stress are obtained and the results fit the test data well. The proposed two types of failure criterion theories can effectively model the strength law of plain concrete under combined compression-shear stress.