Mixed Formulation of Steel-Concrete Sandwiched Beams with Partial Shear Slip

Steel-concrete sandwiched components have recently gained popularity as efficient and cost effective blast resistance systems because of their larger energy dissipation capacity compared to that of conventional reinforced concrete systems. For these sandwiched systems, the shear stress transfer mechanism between steel face plates and surrounding concrete through shear studs, and the resulting shear slip, play an important role in determination of resistance and deformation capacity. This paper presents a performance evaluation of beam-column sandwiched element with partial bond-slip explicitly considering softening and enhancement of compressive strength of concrete material under tensile-compressive and compressive-compressive biaxial stress state respectively based on potential energy functional; and proposes a new two-field mixed-based sandwiched element where independent interpolation functions for the nodal displacements, relative shear slip, and beam section forces are considered. The nonlinear coupled flexural-shear behaviour of the sandwiched element derives entirely from the constitutive laws of the steel, the concrete, and the shear connectors. Shear deformation is considered through the Timoshenko based section kinematics. Distributed inelasticity at the element and section levels are considered through section integration points along the length of the element and material fibre discretization across the cross-section respectively. Multi-axial stress state due to crack-induced anisotropy in concrete fibres is simulated through a fixed crack smeared softened membrane model which is based on the stress equilibrium, the strain compatibility, and the constitutive relationships of materials. The accuracy and efficiency of mixed-based variational principles over widely used displacement-based formulations are assessed by numerical studies of steel-concrete members comparing various response variables such as distribution of shear slip, section forces, and deformations along with capacity-deformation plots, which will in turn pave the way forward for developing performance-based design methodologies for steel-concrete sandwiched structures.