Structural behavior of CHS T-joints subjected to brace in-plane bending at elevated temperatures

Fire resistance of steel joints is one of the major concerns when designing structures against extreme hazards. However, little information is available for Circular Hollow Section (CHS) joints in fire condition, especially forT-joints. In order to gain greater insight into the static behaviour ofCHSconnections, this paper presents an experimental study of CHS T-joints subjected to in-plane bending with variation of brace-to-chord diameter ratios ( & beta;) under elevated temperatures. The tests were conducted with five specimens in isothermal heating condition where the joints were heated to the desired temperatures and then subjected to static load until failure occurred. The failure modes and ultimate strengths of such joints under various isothermal temperatures were investigated and compared with the corresponding joints at the ambient condition. Within the range of investigated parameters, at 700 & deg;C, the joint strength was only 8.40 kNm while at ambient temperature, it was 43.25 kNm. Furthermore, at high temperature, there was a change in the failure modes of the joints. Cracks formed around the weld toes before the joints reach excessive deformation. These cracks affected post-yield strength in moment-rotation curves of the joints. In order to understand the development of cracks around the welded region, material tests were performed to determine the fracture strains of chord material beneath the center weld at high temperatures. To the authors' best knowledge, these structural tests were among the first reported experimental investigations on the ultimate strength and failure mechanisms of tubular joints at elevated temperature.