SIZE EFFECT ON SHEAR BEHAVIOR OF HIGH STRENGTH RC SLENDER BEAMS

Abstract

Nine high strength reinforced concrete beams with minimum shear reinforcement and heavier than minimum as per ACI code, were tested to investigate their size effects on shear strength for medium depth beams (d ranges from 305 to 560 mm), ultimate shear capacity and failure modes. Test variables were shear reinforcement percentage (ρv varying from 0.2682 to 0.3351), longitudinal steel percentage (ρl varying from 2.78 to 3.43) and effective depth (varying from 400 to 500 mm) with constant compressive strength (fck =70 MPa) and shear span to effective depth (av/d) =2.6. This study investigated the influence of beam depth with varying longitudinal reinforcement and minimum shear reinforcement. Test results were compared with the strengths predicted by ACI code, CEB-FIP Model, Zsutty’s equation, Okumaro’s equation and also with Bazant’s method. ACI code and Okumaro’s equation can predict the shear strength trend reasonably well for slender beams. The Bazant’s method is underestimating the ultimate strength. The accuracy of the Zsutty’s equation is relatively better than ACI approaches and but it does not take in to account the size effect. Canadian code provisions correlates well with the experimental results taking in to account the size effect. Keywords: