Nonlinear reinforced concrete frame element with torsion

In this paper an element for nonlinear analysis of reinforced concrete framed structures subjected to torsion is developed using a force-based formulation. The interaction between the axial force and bending moment is taken into account by adopting the Navier–Bernoulli assumption and using the fibre element approach. The torsional DOFs are formulated independently and the effect of normal and tangential forces on the torsional stiffness of section is accounted for by modifying the torque–twist curve of a section under pure torsion. Furthermore, the torsional warping effects on the section stiffness are considered by adding an extra strain field to the section axial strain caused by normal generalised forces. The formulation accuracy and efficiency are verified by some numerical examples.