Performance of an unprotected steel structure subjected to repeated fire at a firefighter training facility

An evaluation of a single story unprotected steel structure exposed to repeated fire during the training of fire fighters is described. Temperatures are monitored on the structure using resistance temperature detectors connected to a data acquisition system. Temperatures of up to 384 °C are measured in the steel of the structures, which are below levels likely to cause much degradation in stiffness or strength. Uniform heating of the columns was shown to result in minimal stresses in the structure as the columns were relatively free to deform axially. Differential temperatures, however, where one side of the member is heated by a greater amount than the opposite side of the member, resulted in stresses calculated using an elastic analysis, up to 16 times greater than the yield strength and can thus explain large permanent curvatures observed in the columns. Coupon tests on steel samples from the columns exposed to repeated fire showed some hardening of the steel, possibility attributed to the plastic deformations in the columns, although the ultimate strain in the material was not greatly affected. Based on the monitoring and analysis, no aspects of the structure are considered to present an immediate hazard to the safety of the users. However, without improved cooling, plastic deformation of some members is expected.