Shear capacity of reinforced concrete deep beams

A mechanism analysis of shear failure of simply supported reinforced concrete deep beams is presented. Concrete and steel reinforcement are modeled as rigid perfectly plastic materials. The failure modes are idealized as an assemblage of rigid blocks separated by failure zones of displacement discontinuity. The shear strength of deep beams is derived as a function of the location of the instantaneous center of relative rotation of moving blocks. Minimization of the developed function gives the shear capacity of deep beams. Comparisons of the predicted shear capacity of numerous deep beams show good agreement with results obtained from experiments. A parametric study of main variables affecting shear strength of deep beams is conducted. The present model shows that the shear-span-to-depth ratio has more influence on the shear capacity than the span-to-depth ratio and as the former increases, the shear strength decreases. Increasing main longitudinal bottom reinforcement increases the shear capacity up to a certain limit beyond which no shear strength improvement could be achieved. The relative effectiveness of horizontal and vertical web reinforcement on the load capacity is mainly influenced by the shear-span-to-depth ratio; the deeper the beam, the more effective the horizontal web reinforcement and the less effective the vertical web reinforcement.