Direct stiffness analysis of a composite beam-column element with partial interaction

This paper presents a stiffness formulation for the analysis of composite steel–concrete beam-columns with partial shear interaction (PI). This formulation is based on the direct stiffness method (DSM). The advantage of the proposed method is that no approximated displacement and/or force fields are introduced in the element derivation, unlike other modelling techniques available in the literature. Some simple structural systems, such as simply supported beams and propped cantilevers, subjected to a point load and to a uniformly distributed load are then considered to validate the accuracy of the results obtained using the proposed formulation against results derived based on closed form solutions; for continuous beams, the results have been validated against those calculated using highly refined mesh of high order finite elements. This has been carried out for different levels of shear connection stiffness to highlight the ability of the proposed method to overcome the curvature locking problems observed in some conventional displacement formulations. The generic applicability of this technique to the analysis of continuous beams is then illustrated, in particular, highlighting its ability to account for material nonlinearities at both service and ultimate conditions.