Direct Answer
HSS members (rectangular, square, and round hollow steel sections) require different fabrication approaches than open sections: end cuts must often be profile-cut or notched rather than square-cut to fit connections, connection welds are made around the full perimeter, and galvanizing requires vent holes. HSS-to-HSS connections involve complex saddle cuts for branch members that typically require CNC profiling.
Full Explanation
HSS fabrication specifics: (1) End preparation — for HSS-to-HSS connections (K-connections, T-connections), the branch member end must be profiled (saddle-cut) to fit the chord member's outer surface. CNC profile plasma cutting achieves the correct geometry. (2) Welds — typically full-perimeter fillet welds or groove welds around the branch. AISC Design Guide 24 governs HSS connection design. (3) Plug welds — HSS columns may require plug welds to the base plate if the fillet weld alone is insufficient. (4) Vent holes — required for galvanizing at prescribed locations. (5) Tolerances — HSS wall thickness tolerance is ±10%, and outside dimensions have ±1% tolerance, which affects connection fit-up calculations.
What This Means for Your Shop
HSS-to-HSS connections are significantly more labor-intensive than open-section connections. A K-connection truss joint where two HSS braces frame into an HSS chord can take 4–8 hours to profile, fit, and weld — versus 1–2 hours for an equivalent open-section connection.
Common Mistakes
Ordering HSS to nominal outside dimensions without accounting for wall thickness tolerance. A 6×6×1/2 HSS with a 10% under-thickness wall has 0.45" actual wall instead of 0.50" — this affects the weld leg available at the corner and the connection capacity.
Recommended Process
Verify HSS material certifications for both size dimensions and wall thickness before fabrication. For HSS-to-HSS connections, develop or obtain a CNC plasma profile cutting file from the detailer rather than manually laying out the saddle cut.