Steel connections: shear vs moment, bolted vs welded, slip-critical vs bearing

One-line orientation

How steel members are joined — by force transferred (shear vs moment) and by method (bolted vs welded, slip-critical vs bearing) — is heavily tested because it controls how the frame behaves under gravity, wind, and seismic loads.

Key points

• By force transferred:
  • Shear / simple connection: joins the web only (clip or seat angles). Carries gravity/shear, allows rotation at the beam end (acts pinned), does not resist bending.
  • Moment connection: joins the flanges as well, making the joint rigid. Transfers both shear and bending moment; comes as fully restrained or partially restrained.
• By method — bolted vs welded:
  • Bolted: fast field erection, less skilled labor; uses high-strength bolts (ASTM F3125 Grades A325 and A490). The older A325/A490 names are still the familiar grade names.
  • Welded: continuous and stiff; a sound weld can be stronger than the base metal, and suits complex geometry — but needs skilled labor, inspection/QC, and control of thermal distortion.
• Bolted connection behavior — slip-critical vs bearing:
  • Use a slip-critical connection when slip would harm performance. Seismic loading alone does not make every bolted joint slip-critical.
  • Bearing (bearing/shear): minor slip allowed; resistance develops when the bolt shank bears on the hole. Simpler and cheaper where slight movement is acceptable.
• Bolted detailing:
  • Standard holes — slightly larger than the bolt for fit-up, often about +1/16 in for common sizes; use AISC/RCSC tables for exact dimensions.
  • Slotted holes — allow movement or tolerance.
  • Washers — distribute load and help maintain preload.

Confusions / comparison

	Shear / simple	Moment
Connected	Web only (angles)	Web and flanges
Transfers	Gravity/shear	Shear + bending
End behaves	Pinned — rotates	Rigid — restrained
Example	Seated/clip-angle connection	Welded-flange (FR/PR) connection

	Slip-critical	Bearing
Resists via	Friction (pretension/clamping)	Bolt shank bearing on hole
Slip	None	Minor slip allowed
Use when	Fatigue, seismic, reversal, slotted holes	Slip acceptable; simpler/cheaper

Related

→ Steel shapes and members (this module): the members being joined · Steel lateral systems (this module): moment connections build moment frames; bolted braces build braced frames · Steel types and production (this module): why weldable low-carbon steel matters.