Shear strength and bearing capacity of reinforced concrete deep beams

Abstract

Reinforced concrete deep beans with small span/depth ratios usually fail by crushing of concrete in the bearing zone above the supports. In order to increase the load carrying capacity of deep beans, bearing strength around the supports should be enhanced. The first part of this study involved the investigation of bearing capacity of plain and reinforced concrete blocks. Effects of edge distance, footing to loading area ratios, heights, base friction and size effect are studied with plain concrete blocks. Bearing capacities of reinforced concrete blocks with different forms, diameter and spacing of reinforcement are also investigated. It is found that interlocking stirrups at small spacing are the most effective form of reinforcement. A failure mechanism for a concrete block in bearing is proposed and found to give the best estimate as compared with other models by different researchers. The second part is concerned with the behaviour of reinforced concrete deep beans with span/depth ratios ranging from 0.7 to 1. 1. These beans were tested under uniformly distributed load at the top. It is found that a shear crack is formed along the line joining the inner edge of the support to the third point at the top level of the bean. The concrete block on the outer side of the crack rotates about the centre of pressure in the compression zone. Shear strength is determined by shear in the compression zone, aggregate interlock of the shear crack and dowel action and the components of forces of reinforcement across the crack. Based on these observations, a model of the failure mechanism in shear is proposed which gives excellent results in comparison with other models proposed