Ultimate limit state design for lateral torsional buckling of partially encased steel beams

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 concrete may slip over steel, crack or crush. Lateral torsional buckling is an instability limit state that may occur in these situations. This paper presents Ansys material and geometric non-linear finite element model for the design of lateral torsional buckling resistance of partially encased steel beam without encasement reinforcements at room temperature. The steel part of the composed section will be modelled by shell, concrete by three dimensional solids and the bond contact with nonlinear spring finite elements. Failure of concrete will also be predicted when the beam is subjected to a constant bending moment