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Structuralaka: rigid connectionaka: fixed connection

Moment Connection

In Plain English

A rigid joint between a beam and column that prevents rotation and transfers bending forces between members.

Definition

A rigid structural joint between a beam and column—or between other members—that transfers both shear forces and bending moments. Moment connections prevent rotation at the joint, allowing the connected members to work together as a rigid frame. They are more complex and costly than simple shear connections but are essential for moment frames resisting lateral loads.

Why It Matters in Bidding

Moment connections are far more expensive to fabricate and erect than simple shear connections, so misjudging how many a structure requires can swing a steel bid substantially. Estimators must read the connection schedule and details carefully because added welding, stiffeners, and inspection drive both shop labor and field hours. Special seismic moment connections also trigger third-party testing that must be priced into the scope.

Example

Reviewing the structural drawings, the steel estimator counts 24 field-welded moment connections at the perimeter columns and adds shop welding, stiffener plates, and UT inspection costs that a shear-connected frame would not carry.

Related Terms

Moment FrameBeamColumnLateral Force

Frequently Asked Questions

They require additional welding, stiffener and continuity plates, tighter fabrication tolerances, and often full-penetration welds that need ultrasonic testing. Field erection is slower because alignment is critical. Each of these adds shop labor, field labor, and inspection cost, so estimators price moment connections at a significant premium over simple shear tabs.
They appear on the structural framing plans and connection schedules, usually marked with specific symbols and detailed on connection sheets. Notes referencing moment frames, rigid joints, or full-penetration welds are indicators. Counting and classifying these connections accurately during takeoff is essential because they cost far more than the typical connections in a frame.
Often yes. Complete-joint-penetration welds in moment connections typically require nondestructive testing such as ultrasonic or magnetic particle inspection, frequently by a third-party special inspector. This testing is a real cost and schedule factor, so estimators should confirm the inspection scope in the specifications and clarify whether it falls to the contractor or owner.

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