Coupled Model for Non Linear Analysis of Reinforced Concrete Members Subjected to 3D Loading

This study presents an inelastic non-linear element with bending, shear, axial force and torsional interaction for seismic analysis of reinforced concrete (RC) structures. This concrete model uses an orthotropic constitutive relation in which the directions of orthotropy are the principal directions of total strain. The model was developed based on softening and confining effects. The shear mechanism along the beam is modeled by using Timoshenko beam approach with a curved three dimensional (3D) frame elements and arbitrary cross-section geometry. The strain field at each concrete fiber of a cross-section is modeled by assuming the strain field of the section as given by the superposition of the classical plane section hypothesis for the longitudinal strain field and a uniform distribution over the cross-section for the shear strain field. Transverse strains are internal variables determined by imposing equilibrium at each fiber between concrete and vertical steel stirrups. The validity of the model is established by correlation of analytical results with experimental tests of RC specimens. The result shows that the energy dissipation and ductility of the RC members decreased significantly under combined bending and torsion.