The strength of reinforced concrete beams in shear

Abstract

Summary This paper deals mainly with the effect of the following factors upon the ultimate shearing strengths of beams:— (i) The percentage and spacing of the web reinforcement for stirrups inclined at 45° to the horizontal. (ii) The ratio of span under shear to the eflective depth for beams with plain webs and for two series of beams with different web ratios. (iii) The percentages of longitudinal compression and tension reinforcement for beams with plain webs and for two series of beams with different web ratios. In the beams with reinforced webs the stirrups were inclined at 45° to the horizontal, and a total of 79 shear failures was investigated from a study of asymmetrically reinforced beams and eccentrically loaded beams. The basic assumptions of the various theories in existence were investigated by numerous measurements of concrete and steel strains, defiexions, and widths of cracks. The results are discussed with regard to existing theories and past research work. It is shown that even small percentages of web reinforcement, below the percentage permitted by the British Code of Practice, were effective in increasing the ultimate shearing failing load. The yield stress of the stirrup was never exceeded and the internal and external shearing forces can only be balanced by assuming that the beam behaves like an open-frame girder. The many theories are compared with the actual failing loads in shear and it is seen that the present British Code of Practice greatly unde~estimates the shearing strength of beams.