Composite beams with both longitudinal and transverse partial interaction subjected to elevated temperatures

This paper presents a novel numerical model for the analysis of composite steel–concrete beams at elevated temperatures accounting for both longitudinal and transverse interaction. The analytical model is derived by means of the principle of virtual work and its accuracy is validated against limit conditions for which analytical solutions are available in the literature. A robust finite element is presented based on the weak formulation of the partial interaction problem. This element is used to perform an extensive parametric study in which the effects of different thermal distributions on the structural response of a composite beam are considered. As the scope of this study is restricted to lower temperatures, elastic material properties are assumed for all materials while still accounting for their degradation with temperature. A bilinear constitutive model is adopted for the transverse interface connection to reflect the more realistic case in which an extremely high connection stiffness exists for the bearing condition of the concrete slab against the steel joist, and a relatively weaker stiffness is manifested when the joist and slab are separating; an efficient iterative procedure has been proposed to obtain the convergence to the final solution. Based on the proposed numerical model, the coupling of the transverse and longitudinal connection stiffnesses are investigated for a wide range of parametric values. This study highlights the importance of accounting for the combined actions, i.e. combined tension and shear force, to better identify the stress state at the interface connection and it is concluded that failure to do so might lead to a significant underestimation of the connectors’ available capacity. Finally, a prescriptive failure criterion based on the von Mises yield condition is proposed for shear connectors and, in the proposed form, is shown to be easily applied and suitable for practical applications.