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Steel connection types: a visual guide

A reference guide to structural steel connections for drawing review and coordination.

Steel connections are where structural forces transfer between members. The connection type directly affects the structural behavior of the frame, whether it resists only vertical loads (shear connections) or also resists rotation (moment connections). Understanding connection types is essential for reading structural drawings, coordinating with the steel fabricator, and identifying potential conflicts with MEP systems.

Key principle

Shear connections allow rotation (simple framing) while moment connections resist rotation (rigid framing). In seismic regions, moment connections must be specially designed and detailed per AISC 358 to ensure ductile behavior during earthquakes.

Shear Connections (Simple Framing)

Shear connections transfer vertical loads only and allow the beam end to rotate freely. They are the most common connection type in steel buildings and are typically shown on the structural framing plan with no special designation.

Single Plate (Shear Tab)
Light to moderate shear loads
A plate shop-welded to the column or girder web, field-bolted to the beam web. The most common simple shear connection in steel construction.
Drawing notation: Shown as a rectangular plate with bolt holes on one side, weld symbol on the other
Double Angle
Moderate to heavy shear loads
Two angles, one on each side of the beam web, bolted or welded to both beam and supporting member. Provides more capacity than single plate.
Drawing notation: Two L-shapes shown straddling the beam web with bolts through all three plies
Single Angle
Light shear loads
One angle shop-welded to the support, field-bolted to the beam web. Economical for lighter loads.
Drawing notation: Single L-shape on one side of beam web
Seated Connection (Unstiffened)
Light to moderate loads
An angle or plate projecting from the column face supporting the beam bottom flange, with a stabilizing clip at the top.
Drawing notation: L-shape bracket below beam, small clip angle at top flange
Seated Connection (Stiffened)
Heavy loads
Similar to unstiffened but with a stiffener plate welded perpendicular to the seat to increase load capacity.
Drawing notation: T-shape bracket below beam with triangular stiffener
End Plate (Shear)
Moderate shear loads
A plate shop-welded to the end of the beam, field-bolted to the supporting member. Quick erection but requires tight fabrication tolerances.
Drawing notation: Plate flush with beam end, bolts through plate to support

Moment Connections (Rigid Framing)

Moment connections transfer both shear and bending moment, creating a rigid joint that resists rotation. They are designated on framing plans with a solid triangle or "M" symbol at the connection point. Moment frames are used for lateral load resistance and in structures requiring rigidity.

Bolted Flange Plate
Moderate moment capacity
Plates shop-welded to the column, field-bolted to beam flanges. Both top and bottom flanges are connected to transfer moment.
Drawing notation: Plates extending from column face to beam flanges with bolt groups
Directly Welded Flange
High moment capacity
Beam flanges directly welded to the column flange using complete joint penetration (CJP) welds. The pre-Northridge standard detail.
Drawing notation: CJP weld symbols at beam flanges to column, shear tab at web
Reduced Beam Section (RBS)
Seismic moment frames
"Dog bone" connection, beam flanges are trimmed to create a controlled plastic hinge away from the column face. Post-Northridge seismic detail.
Drawing notation: Tapered cutouts shown at beam flanges near column, CJP welds at column face
Bolted End Plate (Moment)
High moment capacity
Extended end plate shop-welded to beam end, field-bolted to column flange. End plate extends beyond beam flanges for bolt placement.
Drawing notation: Plate extending beyond beam flanges with bolt rows above and below flanges
Bolted T-Stub
Moderate to high moment
Split-T sections bolted to both beam flanges and column flange. Provides ductile moment connection through T-stem flexure.
Drawing notation: T-shapes at top and bottom flanges, bolted to both beam and column
Post-Northridge Note

After the 1994 Northridge earthquake revealed brittle fractures in directly welded moment connections, FEMA/SAC research led to AISC 358 prequalified connections. Modern seismic moment connections (RBS, BFP, and others) are specifically designed to form plastic hinges in the beam rather than at the weld.

Bracing Connections

Bracing connections join diagonal braces to beams and columns in braced frames. These connections must transfer significant axial forces and require careful gusset plate design.

Gusset Plate Connection
Triangular plate welded to beam/column intersection, brace bolted or welded to gusset. Must be designed for brace axial capacity plus local forces.
Single Gusset (Corner)
Gusset welded to column flange and beam flange/web at corner. Most common for conventional bracing.
Chevron (V-Brace) Connection
Two braces meeting at midspan of beam. Beam must be designed for unbalanced vertical force when one brace buckles.
BRB (Buckling-Restrained Brace)
Pin or bolted connection for proprietary BRB members. Requires specific connection geometry per manufacturer and AISC 341.

Base Plate Connections

Base plates transfer column loads to concrete foundations. The design depends on whether the column is pinned (gravity only) or fixed (moment frame).

Pinned Base Plate
Small plate with 2-4 anchor bolts. Allows rotation. Used for gravity columns and top of braced frames.
Fixed Base Plate
Large plate with 4-8+ anchor bolts, often with stiffener plates. Resists moment. Used at moment frame bases.
Grouted Base Plate
Non-shrink grout fills gap between plate and concrete after column is plumbed. Critical for load transfer.
Leveling Nuts
Anchor bolts with double nuts allow precise column elevation adjustment before grouting.

Bolt Types and Grades

Type
A325 (Group A)
Diameter
1/2" to 1-1/2"
Strength
120 ksi tensile
Use
Standard high-strength bolts for most structural connections
Type
A490 (Group B)
Diameter
1/2" to 1-1/2"
Strength
150 ksi tensile
Use
Higher strength for heavy connections; not to be galvanized
Type
A307 (Grade A)
Diameter
1/4" to 4"
Strength
60 ksi tensile
Use
Non-structural connections: handrails, grating clips, light framing
Type
F1852 (Twist-Off)
Diameter
1/2" to 1-1/8"
Strength
120 ksi tensile
Use
Tension-control bolt equivalent to A325; splined end shears off at target tension

Common Drawing Notation

CJP
Complete Joint Penetration weld, full-strength groove weld
PJP
Partial Joint Penetration weld, specified effective throat
N/S
Near Side / Far Side, indicates weld or bolt locations
TYP
Typical, detail applies to all similar conditions
SC
Slip-Critical, bolts pretensioned for friction resistance
N
Bearing (threads included in shear plane)
X
Bearing (threads excluded from shear plane)
STD
Standard hole (bolt diameter + 1/16")
OVS
Oversized hole (larger tolerance for erection fit-up)
SSL / LSL
Short-Slotted / Long-Slotted holes for movement accommodation

Sources

AISC Steel Construction Manual, 16th Edition

AISC 360-22, Specification for Structural Steel Buildings

AISC 358-22, Prequalified Connections for Special and Intermediate Moment Frames

AISC 341-22, Seismic Provisions for Structural Steel Buildings

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