Effects of elevated temperatures on bolted moment-connections between cold-formed steel members

Experimental investigations at ambient temperature into the behaviour of bolted moment-connections between cold-formed steel members have previously been described. Full-scale joint tests have demonstrated that the channel-sections being connected are susceptible to premature failure, the result of web buckling caused by the concentration of load transfer from the bolts. The results of tests on bolted lap joints have been used to propose design recommendations for the shear strength in bearing of the bolt-hole. For both types of test, the results of non-linear elasto-plastic finite element analyses have been shown to have good agreement. No consideration, however, has been given to the behaviour of such connections at elevated temperatures. This paper describes non-linear elasto-plastic finite element parametric studies into the effects of elevated temperatures on bolted moment-connections between cold-formed steel members. Two issues at elevated temperatures are investigated:
• the reduced moment-capacity of the channel-sections at the joints
• the reduced shear strength in bearing of the bolt-hole, which in fire will be required to resist catenary action. From the results of the parametric studies, simple design rules are proposed that will enable designers to take into account the effects of elevated temperatures.