An Experimental Investigation of Structural Fire Behaviour of a Rigid Steel Frame

Some experimental studies have been conducted on structural fire behaviour of steel sub-frames in order to investigate the effects of thermal stress due to the axial restraint from columns to a heated beam on the behaviour of connections, and its influences on the connected beam and robustness of steel frames. However, the object connections were not beam-to-beam connections but beam-to-column connections with fin plates, end plates, and web cleats. This paper discusses, on the basis of experimental results, structural fire behaviour of a rigid steel frame with fully-moment-resisting beam-to-beam connections with splice plates and HSFG bolts, and beam-to-column connections with full penetration welds. The structural behaviour in the test was also analysed with finite element analysis using Bernoulli-Euler beam elements. The test results indicated that the moment-resisting connections in the rigid steel frame have sufficient load-carrying capacity, but failure may occur in the connected beam due to inadequate shear resistance of the beam web in fire. The critical temperature of the steel beam could be approximated on the basis of its inherent resistance at elevated temperature and initial effects, because the thermal stress disappeared at the fire limit stage. This study was also intended to provide experimental data to help understand the fundamental behaviour of rigid steel frames in fire.