Arch action in reinforced concrete subjected to shear

Abstract

Reinforced concrete elements without transverse reinforcement are vulnerable to shear failure. This premature failure mode prevents structures from developing their full flexural load bearing capacity. It is brittle in nature and occurs with the unstable propagation of cracks and limited preventive signs of distress. Moreover, the associated resistance is difficult to predict with accuracy. This uncertainty can lead to safety risks or inefficient structures. In this research, a novel approach was adopted to study the fundamental behaviour of reinforced concrete subjected to shear and to enhance the shear performance. Innovative specimen geometries and advanced monitoring techniques were used to investigate the interaction between internal resisting mechanisms on specimens with a span-to-depth ratio of 2.5 and a longitudinal reinforcement ratio below 1.3%. Novel configurations were developed through the targeted removal of material, with single or multiple voids denoted respectively Void and Truss. The behaviour of the specimens was enhanced by isolating the internal arch action and increasing the efficiency of the inclined struts. Contrary to common beliefs, it was shown that the targeted removal of material and reduction of internal redundancy can lead to a net increase in the overall resistance and ductility of reinforced concrete structures. Compared to the prismatic reference beams, the shear resistance of the Void and Truss specimens increased by +53% to +122% and the displacements at ultimate loads were 4 to 6 times greater. The isolation of a preferential load-path allowed for greater assurance and control of the resisting mechanism. Consequently, a brittle premature failure due to a critical shear crack was avoided, inducing a ductile failure mode through yielding of the longitudinal steel. Engaging the inherent plasticity of the system led to increased overall resistance and enhanced ductility. These conditions were associated with more reliable and consistent failure loads. The finding of this study can lead to enhanced design and assessment approaches, for the development of safer and more efficient structures.