Shear Behaviour of Ordinary Strength RC Slender Beams

Abstract

To avoid abrupt shear failure, ACI 318 – 08 specifies the requirements for the minimum amount of shear reinforcement for Reinforced Concrete Beams. Minimum amount of shear reinforcement corresponds to a value that restrains the growth of inclined cracking and prevents a sudden shear failure. The factors which influenced the growth and width of inclined cracks have been identified as compressive strength of concrete, shear span to depth ratio, and longitudinal reinforcement. Though significant, few of these factors are not fully incorporated in ACI code 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 investigate the effect of these parameters on shear behavior of the beams, an analytical and experimental study was undertaken on the shear behavior of ordinary strength reinforced concrete slender beams with average longitudinal reinforcement. This experimental study consisted of testing of 8 x simply supported RC slender beams having cross section 10 inches x 18 inches and length of 12 feet subjected to two concentrated load with a shear span of 48 inches and span to depth ratio of 3. In this experimental program 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, two specimen were prepared without any shear reinforcement, two based on ACI code provisions, two Zarari’s (2003) equations, and two based on modification made to Zarari’s equations. Ultimate shear strengths obtained in this experimental program are compared with analytical shear strengths calculated according to ACI code, Zarari’s equation and the Modified Zarari’s equation. Test results exhibit that, modified form of Zarari’s equation is more accurate in prediction of shear strength of beams. On the basis of these test results, it was also found that the minimum amount of shear reinforcement should be such that it allows development of nominal flexural capacity in reinforced concrete beams.