Experimental study of structural fire behaviour of steel beam to concrete filled tubular column assemblies with different types of joints

This paper presents experimental results of structural fire behaviour of steel beam to concrete filled tubular (CFT) column assemblies using different types of joints. The joint types include fin plate, end plate, reverse channel and T-stub. The structural assembly was in the form of a “rugby goalpost”. In each test, loads were applied to the beam and then the structural assembly was exposed to the standard fire condition in a furnace while maintaining the applied loads. In total, 10 tests were carried out. In eight of the 10 tests, fire exposure continued until termination of the fire test, which was mainly caused by structural failure in the joints under tension when the beam was clearly in substantial catenary action. In the other two tests (one using fin plates and one using reverse channels), fire exposure stopped and forced cooling started when the beam was near a state of pure bending and just about to enter into catenary action. The results of the experiments indicate that even the relatively simple joints used in this study were able to allow the beams to develop substantial catenary action so that the final failure times and beam temperatures of the assemblies were much higher than those obtained by assuming the beams in pure bending. At termination of the tests, the beams reached very high deflections (about span/5), even then failure of the assemblies always occurred in the joints. Therefore, to enable the beams to reach their full potential in catenary action, the joints should be made to be much stronger. The results also indicate that reverse channel connection has the potential to be developed into a robust connection characterised by high stiffness, strength, rotational capacity and ductility. The beams in the two cooling tests developed high tension forces, however there was no structural failure in the assemblies. The principal aim of this paper is to present experimental results of joint behaviour in fire (which until now is lacking) to enable development of better understanding and rational design methods for robust construction of joints to resist extreme fire attack.