An experimental study of the behaviour of reverse channel connection components to concrete filled steel tubes under tension at elevated temperature

• New joint type (reverse channel) for connection to concrete filled tubes.
• Detailed experiments to obtain reverse channel web and CFT tube component behaviour.
• Ambient and elevated temperature tests.
• Analytical equations for calculating component ultimate resistances.

This paper presents the results of a series of tests conducted on two components of reverse channel (RC) connection to concrete filled tubular (CFT) column to quantify the load–deflection behaviour of these components at both ambient and elevated temperatures. A total of 21 tests were performed, including 9 tests on the RC component and 12 tests on the face of the CFT section.The RC tests covered two channel widths (150 and 230 mm), two channel web thicknesses (5.5 and 7.5 mm), one and two bolt rows and three temperature levels (20, 550, and 750 °C). The final failure modes were web fracture around bolt hole, bolt pull-out and bolt fracture. Before these final failure modes which exhibited evidences of membrane action, there were evidences of formation of yield lines around individual bolts and formation of yield lines along the length of the channel section. Due to different reductions in strength of bolt and steel plate at elevated temperatures, the failure mode may be different from that at ambient temperature.In the CFT tests, the loads on the tube surface were applied through two plates welded to the tube along the longitudinal direction. The test variables included two types of hollow section (square hollow section (SHS) and circular hollow section (CHS)), two distances between the welded plates (150 and 230 mm) which corresponded to the two RC widths and three temperature levels (20, 550, and 750 °C). Four failure modes were attained: weld failure, column face pull out, loading plate fracture and bolt failure.