Response of steel beam–columns exposed to fire

Steel beams when exposed to fire develop significant restraint forces and often behave as beam–columns. The response of such restrained steel beams under fire depends on many factors including fire scenario, load level, degree of restraint at the supports, and high-temperature properties of steel. A set of numerical studies, using finite element computer program ANSYS, is carried out to study the fire response of steel beam–columns under realistic fire, load and restraint scenarios. The finite element model is validated against experimental data, and the importance of high-temperature creep on the fire response of steel beam–columns is illustrated. The validated model is used to carry out a set of parametric studies. Results from the parametric studies indicate that fire scenario, load level, degree of end-restraint and high-temperature creep have significant influence on the behavior of beams under fire conditions. The type of fire scenario plays a critical role in determining the fire response of the laterally-unrestrained steel beam within a space subframe. Increased load level leads to higher catenary forces resulting in lower fire resistance. Rotational restraint enhances the fire resistance of a laterally-unrestrained steel beam, while the axial restraint has detrimental effect on fire resistance.