Numerical modelling of lateral torsional buckling for partially encased steel beams at elevated temperatures

Partially encased beams are composed structural elements widely used for industrial and commercial buildings with increasing significance. Composite beams may be designed for service load conditions without the collaborative contribution of slabs. Instability problems may occur because concrete may not have the age to resist and also because the concrete may slip over steel, crack or crush. Lateral torsional buckling is an instability phenomenon that may occur in these situations. This paper presents a material and geometric non linear finite element model for determining lateral torsional buckling resistance of partially encased beam without encasement reinforcement in fire conditions. The steel part of the composed section will be modelled by finite shell element, concrete part by three dimensional finite solid elements and the bond contact with finite non linear spring elements, from Ansys. Elevated temperatures will be applied in both four sides of the cross section along the beam, based on the 1S0834 standard fire curve. Failure of concrete will also be predicted when subjecting partially encased beams to fire conditions