Effect of Location of Restraint on Fire Response of Steel Beams

Restrained 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, beam slenderness ratio, location of axial 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 and restraint scenarios. Results from the parametric studies indicate that fire scenario, beam slenderness, location of axial restraint and high-temperature creep have significant influence on the behavior of restrained beams under fire conditions. Severe fires produce high axial forces at early stages of fire exposure; whereas in moderate fires, significant axial force develops only at later stages of fire exposure. Axial restraint enhances the fire resistance due to the development of tensile catenary action in restrained beams. Furthermore, restrained beams with low slenderness ratio exhibit better fire performance when the axial restraint at the support is located at the bottom flange.