Steel Connection Types and Detailing: Shear Connections, Moment Connections, Bolted and Welded Details

Steel structural connections transfer forces between members and determine how a frame behaves under gravity and lateral loads. This topic covers shear (simple) connections, moment (rigid) connections, bolted and welded joining methods, connection detailing for seismic performance, and the prequalified connection standards that govern steel moment frame design.

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Overview

A steel frame is only as good as the joints that hold it together. The way beams attach to columns, braces bolt to gusset plates, and base plates anchor to foundations determines whether a structure acts as a rigid frame, a pinned assembly, or something in between.

Steel connections fall into two broad families. Shear connections (also called simple connections) transfer vertical loads while allowing the beam end to rotate freely. Moment connections (also called rigid connections) lock beam and column together so the joint transfers bending forces and restrains rotation. That single distinction drives everything from frame stiffness to seismic ductility.

The joining method matters just as much as the connection type. Bolted connections use high-strength bolts in bearing or slip-critical configurations. Welded connections fuse members with deposited weld metal, creating continuity that can match or exceed the base material strength. Most real connections combine both: welded flanges for moment transfer, bolted webs for shear.

For the PDD exam, you need to understand how connection type affects structural system classification, how AISC 341 governs seismic detailing, and how AISC 358 prequalifies moment connections proven by testing. You also need to recognize common connection configurations in drawings and understand their load-transfer mechanisms.

Connections are where design intent meets constructability. Getting them right is the difference between a ductile frame that survives an earthquake and a brittle one that does not.

Essential

Every steel connection answers one question: what forces does this joint need to transfer? The answer splits the world of connections into two categories, and then the joining methods add another layer of decisions. ## Shear Connections (Simple Connections) A shear connection transfers vertical reaction forces from a beam into a column or girder while allowing the beam end to rotate. Structurally, this behaves like a pin. The beam is free to deflect under load without inducing significant bending moment into the column. Common shear connection types include: Single-plate (shear tab): A plate welded to the column and bolted to the beam web. This is the most common shear connection in steel construction because it is economical and easy to erect. The plate is typically shop-welded to the column, and the beam is field-bolted through the web.

Professional

An architect working on a six-story office building in SDC D faces a structural engineer's recommendation for a special steel moment frame. The connection type choice will ripple through the project's cost, schedule, and quality control requirements. The engineer specifies reduced beam section (RBS) connections for the moment frames. This is a common choice for special moment frames because the RBS is well-tested, eliminates the risk of weld fracture at the column face, and avoids the need for heavy reinforcement plates. But the flange cuts require precise fabrication. The shop drawings will show the exact radius and depth of each cut, and the structural steel fabricator needs CNC equipment or careful template work to execute them. Consider the coordination implications. The RBS creates a wider beam at the connection zone, which may conflict with fireproofing profiles, architectural column covers, or ductwork routing.

TLDR

Shear connections transfer vertical loads only; beam end rotates freely (pin behavior). Common types: shear tab, double angle, seated connection.
Moment connections transfer shear, axial force, and bending moment; beam and column act as a rigid unit. Required for moment frame lateral systems.
Bolts come in two categories: bearing-type (load through bolt shank bearing) and slip-critical (load through friction between clamped surfaces).
Welds follow AWS D1.1. Fillet welds are most common; CJP groove welds are required at moment connection flanges.
Fillet weld effective throat = 0.707 x leg size.
AISC 341 governs seismic detailing for all steel SFRS members and connections.
AISC 358 prequalifies tested moment connections (RBS, extended end plate, bolted flange plate, etc.) so project-specific testing is unnecessary.
Strong column, weak beam: plastic hinges must form in beams, not columns or connections.
Post-Northridge lesson: improved weld metal toughness and modified connection geometry (like the RBS) are now required for seismic moment connections.
Special moment frames must sustain 0.04 radian interstory drift through inelastic rotation per AISC 341.

ELI5

Think of building with steel beams and columns like building with an erector set. The pieces themselves are strong, but the whole thing only works if the joints hold. There are two ways to connect steel beams to columns, and they do very different things. Simple connections (shear connections) are like a door hinge. The beam can swing a little at the end. It holds the beam up and stops it from falling, but it does not stop the beam from rotating. These connections transfer weight straight down. Most beams in a building use this type because it is simple and cheap. Rigid connections (moment connections) are like gluing two Lego bricks together. The joint is locked solid. The beam cannot rotate where it meets the column. This means the whole frame acts as one stiff piece.

AREProject Development & Documentation

Steel Connection Types and Detailing: Shear Connections, Moment Connections, Bolted and Welded Details

2 min read230 words

Why Steel Connections Define Structural Behavior

Connections are where design intent meets constructability. Getting them right is the difference between a ductile frame that survives an earthquake and a brittle one that does not.

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