A simple mixed finite element model for composite beams with partial interaction

A simple and effective mixed finite element model is proposed for studying the behavior of beams with composite section, with particular reference to two-layer beams with partial interaction, namely, steel–concrete, timber–concrete, and two-layer laminated glass beams. The model is based on a mixed variational formulation, which as independent fields assumes the displacements of each layer and the shear stresses transmitted by the connections between the layers. The effectiveness of the model, which automatically satisfies the Newmark kinematic hypothesis for a composite beam, is evaluated by performing a set of numerical tests and comparing results with existing analytical and numerical solutions; furthermore, the convergence of the model to the well-known layered and monolithic beam behavior is shown. Numerical tests are performed in the linear elastic field, but the possible model extensions to the field of material and geometric nonlinearity are highlighted, together with a further refinement of the numerical model.