Double-HSS Seismic Resistant Beam-to-Column Moment Connections

Abstract

Hollow structural sections (HSSs) are highly efficient in resisting compression, torsion, and bending. Their high torsional rigidity generally eliminates lateral-torsional buckling (LTB), which in turn eliminates the need for lateral bracing in flexural members. As a result, their plastic rotational capacity is mainly governed by flange local buckling (FLB) and web local buckling (WLB). Moment-resisting connections for single-HSS flexural members can be complicated. This study investigates the behavior of double-HSS flexural members under large displacement reversals. The study configuration consists of a double-HSS beam connected to a column through a center gusset plate secured by flare-bevel groove welds. The advantages of the proposed double-HSS moment connection are: (1) compared to a single-HSS, it effectively reduces the width-thickness ratios (b/t) of the flanges by using a double-HSS, thereby considerably increasing the member’s compactness and ductility; (2) it provides simple and practical connection details between the beam and column; and (3) it eliminates the need for lateral bracing. In addition, on-site welding can be eliminated by using shop-welded double-HSS beam-column stubs spliced by a bolted end connection. Experimental tests indicate that the proposed double-HSS moment connections showed a stable response up to a story drift angle of approximately 0.07 rad for the HSS sizes tested. Nonlinear finite-element analyses, including fracture behavior via the extended finite-element method (XFEM), were used to simulate test results, and finite-element analysis (FEA) was used to formulate the design procedure for the center gusset plate and welds connecting the double-HSS beam and column flange.