Study On Fire Resistance Of Welded K - Type Round Steel Tube

This paper is mainly focused on studying the fire resistance and the failure mode ofcircular hollow section (CHS) tubular K-joints at elevated temperature under brace axialloading. Experimental tests on two full-scaled CHS tubular K-joints are carried out toinvestigate the mechanical behavior of the specimens at elevated temperature. Thetemperatures on the tube surface and the displacement at some critical positions such ascrown, saddle and brace end are measured. Experimental results indicate that the failure ofCHS K-joints occurs suddenly when the temperature on the specimens exceeds a criticalvalue. The temperatures development at different measurement points on the chord surfaceare almost same. Comparatively, the temperatures at different time on the brace surface arealways higher than the corresponding temperatures on the chord surface. Generally, thefailure process can be divided into three distinct stages due to different deformingmechanisms. It can also be observed that the final failure modes of both of the K-jointspecimens are characterized by local plastic yielding. In addition, an indirect sequentiallycoupled thermal-stress analysis model is proposed for studying the fire resistance ofCircular Hollow Section (CHS) Tubular K-joints. The accuracy and the reliability of thepresented model are verified by comparing finite element results with experimentalmeasurements. Deforming rate criterion is selected and defined to determine the criticaltemperature of a tubular K-joint in fire because failure occurs quickly when deformingrate exceeds a certain value. Afterwards, a preliminary parametric study is conducted tostudy the effects of some parameters on the temperature development and on the criticaltemperature of a K-joint. These parameters include convection coefficient, radiationcoefficient, loading ratio, geometrical parameters β(brace-to-chord diameter ratio), γ(chordwall slenderness ratio), θ(brace-to-chord inclination angle), and initial chord stresses. Theresults show that the convection and the emissivity have no effect on the criticaltemperature of K-joints but have great effect on temperature development and on fireendurance time. The critical temperature of a K-joint is slightly enhanced with thedecrease of β and θ. However, with the increase of γ, the critical temperature decreases slightly. Furthermore, it is also found that parameters β and θ have a slight influence onthe critical temperature. The results also indicate that the critical temperature of a K-jointdecreases rapidly with the increase of loading ratio and initial chord stresses. Furthermore,a simple yet reliable and accurate designed equation is proposed for predicting the staticstrength of tubular K-joints at elevated temperature.