Behaviour of bolted rigid joint with endplate under localised fire scenario

Abstract

The bolted endplate rigid connections in steel structures are used due to their robustness in distributing forces between the connected members. Though numerous studies have been performed to investigate the response of endplate connections under conventional fires representing uniform temperatures throughout the members (ISO-834, ASTM E119, etc.), the response of the same in case of localised fire is still not explored fully. The present paper focuses on an investigation of the behaviour of a moment resisting frame (MRF) assembled with flush endplate connection with bolts as connecting medium under localised fire scenario using Finite Element (FE) technique. A series of cases with different magnitudes of applied loads was investigated. In all the cases, the frames were heated up to failure with the localised fire source underneath the beam midspan and the corresponding failure modes were investigated. Experiments were performed on the samples of material at high temperature to gather a firsthand information on material characteristics. The frames experienced member failure at the zone of maximum temperature in the beam (midspan) for load level up to 30% of its ultimate capacity, whereas for load level above this, the frame failed at the connecting bolts of grade 5.6, which were maintained at room temperature. Based on the numerical study, it was observed that the provisions of IS 800:2007 were conservative than EN 1993-1-8:2005 in evaluating the safety of bolts under localised fire scenarios. Finally, parametric studies with the variation in connection geometry and configurations were performed, and design suggestions were recommended.