Influence of span to depth ratio on the shear strength of reinforced concrete deep beam

Abstract

A total of twenty five brick aggregate reinforced concrete deep beams have been tested in this study in order to investigate the influence of span to depth ratio on the shear strength of reinforced concrete deep beam. The test beams were single span and simply supported type. The beams were divided into five series according to their span to depth ratio (LID = 1 to 5). The first beam of each series was designed and detailed as per the recommendations of ACI Building Code (ACI 318-89). In the other four beams of each series, the amount of either flexural or horizontal web reinforcement or both were changed in relation to those of first beam of the corresponding series. All the beams were tested under single concentrated loading at mid span. The effects of different web steel arrangement and span/depth ratio on cracking load, ultimate load, crack patterns and modes of failure were investigated. It was observed in the study that the amount of both flexural and horizontal web reinforcements influenced the diagonal cracking load and the ultimate load capacity of test beams to some extent. It was also found that the change in the amount of either the vertical or the horizontal web reinforcement alone could not bring a significant change in the load carrying capacity of test beams. After comparing the observed initial cracking stress with that of by de Cossio(9), Kabir(7) and Rashid(10) , it was found that the observed initial cracking stress was very close to the stress calculated by de Cossio(9). It was also observed that the shear strength capacity of the deep beam having LID ratio five was very close to the shear capacity of ordinary rectangular beam of similar size. In general the ACI 318-89 recommendations regarding the ultimate strength of deep beams were observed to be conservative. Some available formulae (e.g. ACI 318-89, Ray & Reddy and Ramkrishnan & Ananthanarayana) were used to estimate the ultimate load in shear of deep reinforced concrete beams. It was shown that all the three formulae can be used efficiently to determine the ultimate shear strength of deep beams but these formulae need some modifications as proposed by Kabir(7) and Rashid(10).