Evaluation on fire resistance of tubular K-joints based on critical temperature method

Abstract

This paper proposes a design method for evaluating the fire resistance of circular hollow section (CHS) tubular K-joints subjected to axial loading based on a critical temperature method. In this method, a tubular K-joint is considered to be safe when the joint temperature is lower than a critical temperature. Through finite element (FE) analyses, it is proved that the temperature development of a steel tube in fire condition can be taken safely as the temperature development of a tubular K-joint with a chord same as the steel tube. Afterwards, an extensive parametric study is carried out to investigate the effect of geometric parameters including β, γ and θ on the critical temperature of tubular K-joints. It is found that the critical temperature for a tubular K-joint without initial chord stress is merely related to the degree of utilization, and the effect of geometric parameters on such critical temperature can be ignored. The results also show that the critical temperature of a tubular K-joint subjected to balanced axial loads can be calculated on the basis of the equation for predicting the critical temperature of a steel member specified in Eurocode 3 (part 1-2). Moreover, the influence of the chord stress on the critical temperature is investigated through the numerical results of 30 FE models. The results show that the relationship between the critical temperature and the chord stress can be simplified as a parabolic curve for designed purpose.