The ultimate strength of reinforced concrete beams in shear

The ultimate strength of reinforced concrete beams of both rectangular and tee section under the combined effect of bending and shear forms the topic of this investigation. The published results of tests on over 1000 rectangular and tee beams have been collected and the ultimate strength of each of them predicted from an empirical formula. The overall coefficient of variation of the ratio of predicted to observed strengths is found to be about 18%. By simulating the anticipated variations in the parameters of the empirical formula it has been shown that the overall variation in the results is not excessive. Over 200 new tests on beams of reinforced plaster both rectangular and tee sections, and also the previously published test results on plaster beams support the general form of the empirical formula. Fourteen new tests on reinforced concrete tee beams with short shear spans indicate that the behaviour of such tee beams can be predicted as confidently as that of rectangular beams. The proposed empirical formula will successfully predict the strength of beams tested in the restrained condition and also under uniform load. This is supported by further tests on reinforced plaster beams. The mechanism of shear in reinforced concrete beams is explained by quoting the test results of other investigators and also by the present tests on plaster beams. It will be shown that bond between the reinforcement and concrete is a fundamental factor which influences shear failures. The load factors of the simply supported beams implied by the shear clauses in the current British Code, the current American Code and also by the proposed British Code are compared. The reliability of such predictions is examined. The economic design of reinforced concrete beams is examined by different approaches and the cost is compared. It is suggested that the cost of shear reinforcement is a very small part of the total cost of such beams.