Reinforced Concrete Beams Subjected to Bending and Torsion

A diagonal compression field theory was extended to study the post-cracking behavior of reinforced concrete sections subjected to combined axial force, biaxial bending, and torsion. The theory assumes that when concrete cracks are formed by the torsion, the reinforced concrete member becomes a hollow section with varied wall thickness, which is then discretized into a wall element system. With the consideration of equilibrium and compatibility conditions, the theory converts the problem to that of solving a system of nonlinear equations. An examination of the model’s response in limiting loading cases indicated that the proposed method provides a single model unifying the pure torsion and pure bending theories. The proposed theory was calibrated with experimental data for combined bending and torsion of both rectangular and slab sections. The comparison indicated that the post-cracking behavior is in general well predicted by the model. The proposed theory can be employed to determine the moment (curvature and torsion) twist response of general reinforced concrete sections subjected to combined loadings.