HSS-to-HSS seismic moment connection performance and design

• HSS-to-HSS moment connections' finite element models are developed and analyzed.
• Unreinforced HSS-to-HSS connections do not develop the beam plastic moment capacity.
• Reinforced connections meet current seismic requirements for all β values.
• Beam thickness–column thickness ratio of 0.6 maximizes reinforced connection capacity.
• A capacity based seismic design procedure is derived for reinforced connections.

Hollow structural sections (HSS) provide an alternative to typical wide flange sections in low-rise seismic moment resisting frames. Their beneficial strength-to-weight ratio as well as bending, compression, and torsional resistance increases the versatility of moment frames and potentially improves performance under earthquake loads. With an understanding of current design requirements for seismic moment connections and static HSS-to-HSS connections, 39 fully welded unreinforced HSS-to-HSS connections are explored through finite element analyses. However, performance is limited due to column face plastification and inability to develop the plastic moment capacity of the beam. To rectify this problem, 24 through plate and 24 external diaphragm plate HSS-to-HSS moment connections are analyzed. Several important geometric parameters, such as the beam width–column width ratio, beam thickness–column thickness ratio, plate length, and plate thickness are considered to understand their effect on the connection moment capacity and sources of inelastic rotation. The through plate and external diaphragm reinforcement greatly improve the connection behavior moving yielding away from the column face and into the beam member. The results from the reinforced connections are used in combination with current seismic design provisions to develop a design procedure that optimizes the performance of these connections. The reinforced connections can be detailed to develop plastic hinging in the HSS beam member while minimizing the likelihood of a non-ductile weld failure.