Moment Frame vs. Braced Frame: Cost Comparison
Braced frames typically cost 15-30% less than moment frames for the lateral system, because braced frames use simple shear connections plus diagonal members while moment frames need expensive rigid beam-column connections with full-penetration welds and heavy inspection. The trade-off is architectural: braces obstruct space, moment frames leave it open. The choice is made at schematic design — switching late is redesign.
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Where the cost difference comes from
Moment frame connections are the expensive part: full-pen welds, weld access holes, continuity plates, and ultrasonic testing of every weld, plus the heavier columns needed for frame stiffness. A single special moment frame connection can cost $2,000-$5,000 installed and inspected. Braced frames use standard shear connections (cheap) and add diagonal members (cheap steel, simple connections) — the economy is in the connections, not the member weight.
Architectural and functional trade-offs
Braces need diagonal space — they block windows, doors, and open floor areas, which is why you see them in warehouses and industrial buildings but rarely in office facades. Moment frames keep bays open for storefronts, parking entries, and architectural expression. Eccentrically braced frames (EBFs) split the difference: the link beam yields in earthquakes while the bracing stays out of the way of most openings.
Seismic detailing multipliers
In high seismic zones, special moment frames carry the strictest detailing and inspection requirements in the code — the cost premium over braced frames grows. Ordinary moment frames are cheaper but heavily restricted in seismic design categories. The structural engineer runs the comparison at schematic design with real member sizes and connection counts, because rules of thumb mislead on irregular buildings.
The bottom line
Braced frames cost 15-30% less than moment frames but obstruct space; moment frames buy openness at the price of expensive connections and inspection. Decide at schematic design with real numbers.
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