Behaviour of square hollow section brace-H-shaped steel chord T-joints under axial compression

Abstract

To research mechanical behaviour of square hollow section (SHS) brace-H-shaped steel chord T-joints under axial compression, eight different β joint specimens with different external stiffeners arrangements at the foot of SHS brace were tested under axial compression in brace. The axial compression force was applied to the top end of the SHS brace member, which was weld to the center of the chord member. The test procedures, joint failure modes, jack load–vertical displacement curves and jack load–strain intensity curves were presented in the paper. The effect of β (defined as the brace width to the flange of H-shaped steel chord width ratio) and the external stiffeners at the foot of SHS brace on the mechanical behaviour of the T-joints was also studied. The corresponding finite element analysis was also performed and calibrated against the test results. An extensive parametric study was carried out to evaluate the effect of geometric parameters on mechanical behavior of the T-joints under axial compression. Results of these tests show that local buckling failure of brace member was the main failure mode observed during the tests. 45° oblique external stiffeners could not improve the ultimate capacity of unstiffened joints under axial compression, while 90°normal external stiffeners could effectively improve the ultimate capacity of unstiffened joints with large β, even decrease the ultimate capacity of unstiffened joints with small β. Increasing the thickness of stiffeners can slightly improve the ultimate axial compressive capacity of stiffened joints. It is shown that the design strengths predicted by the current design rules are conservative for the unstiffened test specimens. The joint strengths obtained from the parametric study were compared with the design strengths calculated using current Eurocode 3. It is shown from comparison that the current Eurocode 3 is dangerous for the SHS brace-H-shaped steel chord T-joints under axial compression. The new design equations were proposed for the SHS brace-H-shaped steel chord T-joints under axial compression, which were verified to be safe and accurate.