Evaluation of shear and diagonal tension in plain concrete

Shear strength is an important property in civil engineering materials and structures. Several practical concrete structures result in loading conditions with high shear and low moment such as corbels, brackets, composite floor systems and bridge decks. Shear failure in concrete is undesirable due to the brittle nature of failure. In addition, it remains difficult to predict accurately, despite all the research in the area. Experimental and analytical work has been conducted to investigate a modified Iosipescu test as a means of measuring the direct shear strength of plain concrete beams. The Iosipescu loading configuration results in shear failure in a predefined plane, and the failure path is completely contained within the region of high shear. While other researchers have argued different failure modes for similar loading configurations, it is concluded from this study that high shear stress along the failure plane causes high principal tension. Finite element analyses show that the failure planes observed in the specimens are defined by the orientation of principal tensile stress. Combined with the experimental results, these finite element analyses provide a means to predict failure based on the magnitude and orientation of the principal tensile stress.