Development of Analysis Tools for RC Members Subjected to Three-Dimensional Combined Loads

This paper presents a new finite element-based model for analysis of reinforce concrete (RC) frames subjected to combined loading conditions. The proposed model is formulated to address the interaction between the axial force, biaxial shear, biaxial bending, and torsion. The shear mechanism along the beam is modeled by using the Timoshenko beam approach with curved three dimensional (3-D) frame elements with arbitrary cross-section geometry. The problem consists of solving a system of equations by combining the equilibrium conditions, compatibility conditions and constitutive laws of materials at the section and structural level. The concrete constitutive model follows the Softened Membrane Model (SMM) with a tangent-stiffness formulation. The validity of the model is established by correlation of analytical results with experimental tests of RC specimens. The result shows that the flexural capacity and ductility of the RC members decreased significantly under the effect of combined bending and torsion.