Effect of Restraint Force Location on the Response of Steel Beams Exposed to Fire

Abstract

Restrained steel beams, when exposed to fire, can develop significant fire-induced restraint force. In most previous studies, the location of the fire induced restraint force was always assumed to be situated at the center of gravity of the beam cross section. In practice, the location of axial restraint force can vary depending on many parameters, including the configuration of the connection at the supports of the beam. A set of numerical studies is presented to illustrate the response of unprotected steel beam-columns under realistic fire, load, and restraint scenarios. Results from the parametric studies indicate that fire scenario, beam span, and restraint conditions have significant influence on the behavior of restrained beams under fire. High intensity fires produce high axial forces at early stages of fire exposure, whereas in mild fires, significant axial force develops only at later stages of fire exposure. Presence of axial and rotational restraint enhances the fire resistance of beams due to the development of tensile catenary action. Overall, the fire response of restrained beams generally improves when the axial restraint is located in the bottom flange.