A 3D beam element to study torsion of steel open sections exposed to fire

In the analysis of structures in fire, numerical models must account for the effects of increasing temperatures. Although different finite elements capable of effectively tackling the problem are available, 3D beam elements employed in many commercial software do not properly account for the degradation of the torsional properties with temperature. In this context, an enhanced 3D beam element based on a co-rotational formulation is proposed. The element was specifically developed for steel elements and is well suited for the analysis of structures that exhibit a significant torsional behavior. The Timoshenko beam theory was employed and the steel stress-strain law and thermal expansion were implemented according to EN1993-1-2. Two different case studies are presented in this paper. Numerical analyses by means of two different software (ABAQUS and SAFIR) were performed and compared to the results. The outcomes confirmed the effectiveness of the proposed element.