Mixed Formulation of Inelastic Composite Shear Beam Element

This study presents a new beam element formulation following a Hellinger-Reissner functional for composite members considering coupling between bond-slip and shear deformations. A robust state determination along with new stability criteria for the mixed-based formulation are proposed. The constitutive laws of the concrete, steel, and shear connectors are used to derive the inelastic coupled axial-flexural-shear interaction of the composite element. To consider shear deformations, Timoshenko beam theory has been adopted in deriving the section kinematics equations. The J2 plasticity following a radial return mapping algorithm and a fixed crack smeared softened membrane model are used to simulate the multiaxial stress state in steel and concrete, respectively. The accuracy and efficiency of the mixed-based formulation was evaluated by comparing the responses at local and global levels with the displacement-based formulation. (C) 2020 American Society of Civil Engineers.