An experimental study on double longitudinal plate connection for steel T-joints subject to out-of-plane moments

Square hollow section (SHS) is widely used as a chord member in steel trusses. In one connection type, a brace using I-shape or box section at a T-joint transfers out-of-plane bending moment to these chords through double longitudinal plates. Design codes include rules for different connections to hollow sections, but not specifically for this detail. An experimental program is presented in this paper to verify relevant design rules and apply them to the double-plate connection, considering three key parameters: double-plate spacing, connection offset from the chord centerline, and plate width. The test results are evaluated by discussing the connection capacity and the observed failure modes, in addition to plotting both the load-displacement and moment-rotation curves. Applying relative rules from code is found to be on the conservative side and requires adjustment to apply to the current context. However, the rules for single plates are found to be adequate for some of the eccentric double-plate connections with a plate at the chord face center. Some modifications to the existing design rules are proposed to suit the eccentric connection with a plate not at the center.