Shear Behaviour of Ordinary Strength RC Slender Beams

Abstract

Major factors contributing to the shear behavior in reinforced concrete (RC) beams have been identified as compressive strength of concrete, shear span to effective depth ratio, and longitudinal reinforcement. Though significant, few of these factors are not fully incorporated in ACI code provisions for design of minimum shear reinforcement. The effect of these factors on shear behavior of RC beams have been studied analytically by Zararis (Zararis, 2003; Zararis and Papadakis, 2001) but have not been validated experimentally. To clarify the anomaly and to investigate the effect of these parameters, an analytical and experimental study was undertaken on the shear behavior of ordinary strength RC slender beams with moderate longitudinal reinforcement. Based on this study, modification to Zararis (2003) equations is proposed on shear behavior of RC beams. The experimental program consisted of testing of eight simply supported RC slender beams subjected to two concentrated loads with a shear span of 1016 mm (a/d = 2.5). Test specimens were divided into four groups based on amount and spacing of minimum shear reinforcement in RC beams. For comparison and experimental validation of minimum shear reinforcement in RC beams, specimens were prepared without shear reinforcement, based on ACI code provisions, Zararis (2003) equations, and modified equations presented in this study. Ultimate shear strengths obtained in this experimental program are compared to the analytical shear strengths calculated according to ACI code, Zararis equation and the modified equation. Test results exhibit that, the proposed equation gives more accurate prediction of shear capacity of RC beams. Based on the test data, it was also found that minimum shear reinforcement should be such that it allows development of nominal flexural capacity in RC beams; accordingly, a new expression for calculating minimum shear reinforcement is also proposed which incorporates all contributing factors.