Evaluation of the slotted-hidden-gap (SHG) connection for square HSS brace members

Abstract

Hollow structural section (HSS) braces of concentrically braced steel frame structures are often connected using a knife connection, which creates a net area in the brace due to the slot. Tensile rupture of the brace's net section is the controlling failure mode unless reinforcing schemes are utilized. The “Slotted-Hidden-Gap (SHG)” connection, in which a notch is created in the gusset plate to overlap the gross area of the tube to eliminate the net area, represents an attractive alternative to traditional connection reinforcements; however, no design guidelines exist for the SHG connection for square HSS braces. A laboratory testing program and finite element modelling were carried out to determine the minimum overlap length required to develop the yield resistance of a square HSS brace. The test program included monotonic tensile loading tests on short conventional- and SHG- connection specimens, and one reversed cyclic loading test on a 4.86 m long brace specimen with SHG connections. An overlap length of 5% of the weld length was sufficient to develop the yield resistance of the braces with SHG connections. For those specimens, the HSS eventually fractured on their gross area away from the connections, after experiencing extensive yielding along their length. Conversely, braces with the conventional connections suffered localised yielding and fracture at the net section. The long brace with SHG connections attained its yield tensile resistance, including a 15% increase due to strain hardening, while sustaining an axial deformation corresponding to a storey drift of 3.14%.