Flexure-Shear Interaction Model for Longitudinally Reinforced Beams

An analytical model is proposed for predicting the relative flexural capacity, i.e. the ratio of the moment capacity with interaction to moment capacity in pure flexure. The study concerns longitudinally reinforced concrete beams or one-way slabs without shear reinforcement failing under the combined influence of fleuxure and shear. For these structural elements, it is possible to obtain the 'valley of diagonal failure.' Moreover, an expression is determined giving the a/d ratio at which the minimum value of the flexural capacity under shear and moment interaction is attained. At the minimum flexural capacity, the moment contribution due to beam action is analytically found to be 60% of the total capacity. It is further shown that the expression for the a/d ratio corresponding to minimum flexural capacity also gives the critical a/d ratio distinguishing failure at diagonal cracking from failure by crushing or splitting of the concrete.