Development of a rational procedure for shear design in structural concrete

Abstract

Over the last century, the design for shear in reinforced concrete beams has been uncertain. The reason for this uncertainty is the lack of clear understanding of the true nature of load carrying mechanism. Researchers around the world have developed several shear design procedure as a remedy to this uncertainty. Most of them are empirical and some are rational which use various mathematical representations of load carrying mechanism. Almost all of these mathematical models are complicated and accuracy of is rather low compared to empirical methods. With the advancement of concrete technology and introduction of new methods, the improvement of accuracy of shear design methods is rather unmatchable when compared with flexural design. However, some of the new shear design methods were adopted by codes of practice and the design formulae were modified by introducing various empirical factors based on test. So the shear design has now become very much empirical. Some of the developed rational methods give good representation of the load carrying mechanism of beams. The method proposed here with the objective of developing a rational yet simple method, also assumes the load carrying mechanism of a beam as a truss. The tension carrying member represents the stirrups and the concrete portion is represented by compression member. For this proposed method, the compression carrying concrete member is idealized as a cylindrical element applied with axial compression. The behavior of this idealized cylinder is modeled by using mathematical techniques like Isotropic and Anisotropic analysis. This developed method is compared with several key codes of practice using available test data for accuracy. It is found that the proposed method is giving sound representation of the test results compared with most other codes of practice. According to the comparison, it is clear that this method is only second to Japanese code of practice.