Tension stiffening in concrete beams. Part 1: FE analysis

Although after cracking, concrete has negligible tension capacity, the intact concrete between cracks within the tension zone of a reinforced concrete beam can still develop significant tensile stresses to contribute to the flexural stiffness of the concrete beam. Such a tension stiffening effect in a flexural member is not quite the same as that in an axial member because the tensile stresses in a cracked flexural member are induced not only by the steel reinforcement–concrete bond but also by the curvature of the flexural member. In this study, the tensile stresses developed in cracked concrete beams are analysed using a finite-element (FE) model that takes into account the non-linear biaxial behaviour of the concrete and the non-linear bond stress–slip behaviour of the steel reinforcement–concrete interface. Based on the numerical results so obtained, a tensile stress block is proposed for section analysis of the moment–curvature curves of reinforced concrete beams at both the uncracked and cracked states. It will be shown in part 2 of this paper that the tensile stress block may also be used for member analysis of the load–deflection curves of concrete beams without resorting to FE analysis.