Torsion–shear–flexure interaction in reinforced concrete members

Abstract

Synopsis An analysis for predicting stresses, strains and rotations at all levels of load and for predicting the strength of members under combined torsion–shear–flexure loads is presented. Equilibrium and compatibility are considered and the analysis predicts the phenomenon of ‘shear relief’, whereby the torsional strength of an over-reinforced beam is enhanced by a small shear load. A torsion–shear–flexure interaction surface is proposed which is actually a combination of two surfaces. An equation defining the space curve formed by the intersection of these two surfaces is derived. Use of this equation indicates the portion of the interaction surface that is appropriate for a particular combination of loads. The proposed interaction surface is compared with test results available in the literature and good correlation is noted.