Analytical approach to failure surfaces in reinforced concrete sections subjected to axial loads and biaxial bending

This paper proposes an analytical approach to calculating failure surfaces in rectangular reinforced concrete cross sections with symmetrical reinforcement when submitted to axial loads and biaxial bending. The analytical method is valid for concrete with a strength of between 25 and 80 MPa. The failure surface is obtained by means of reference generatrices that lie on two directrices corresponding to two known axial loads and on the maximum and minimum axial capacity of the section. The proposed expression was assessed with results obtained from experimental tests (from the literature) and from a numerical model. This approach enables the section capacity to be verified and the reinforcement designed to a sufficient degree of accuracy for everyday professional practice. The method is easy to use and may be extensively applied to reinforced concrete columns in buildings.