Shear strength of RC deep beams

This paper reports on some experimental investigations on the shear behaviour of reinforced concrete (RC) deep beams without and with shear (web) reinforcement. Twelve large scale deep beams made of 60MPa concrete were tested. Three different beams of depth 250 mm, 500 mm and 750 mm were tested to understand size effect. The behaviour of deep beams including load-deflection curves, web strains and crack width, shear ductility and reserve strength has been investigated. The beams tested under three-point loading failed in shear and failure modes were influenced by the beam depth and amount of shear reinforcement. The shear strength was found to decrease with increase of beam size and large size beams exhibited brittle failure, which was attributed to size effect. Sufficient shear reinforcement in beams turned brittle failure in to ductile. The load-deflection curves are regular in small size beams with heavy shear reinforcement. The web strains and the width of shear cracks increase at failure with web reinforcement. With increased quantity of shear reinforcement, more confinement is offered to sustain greater web strains and crack widths. Shear ductility (=capability of withstanding severe cracking and deformation) decreases in deep beams and increases in highly shear-reinforced deep beams. Significant reserve strength beyond diagonal cracking was observed in deep beams. Asa matter of fact, this reserve strength was to two times larger in small-size beams, compared to large-size beams.