The member schedule is not the tonnage
A structural steel member schedule — typically on sheet S-001 or S-002 — lists every beam, column, brace, and girder with its wide-flange designation, length, and weight per foot. Sum the weights across the schedule and you have the "shape tonnage." What you do not have: the connection steel, the bolts, the shear studs, the base plates, the stiffeners, the doubler plates, the misc metals carved out of the structural scope.
The industry rule of thumb is that connection steel adds 8-12% to shape tonnage on a typical commercial braced frame, 12-18% on a moment frame, and 15-22% on a seismic-designed moment frame in SDC D. If your bid applies a flat 10% across every project, you are overbidding simple gravity frames and underbidding moment frames — in exactly the pattern that loses the cheap bids and wins the hard ones.
Connection typing is where the money lives
AISC 360-22 recognizes three primary connection types: simple (shear), fully restrained moment (FR), and partially restrained (PR). Simple connections are typically double-angle, shear tab, or end plate — fabrication is fast, bolt count is modest, connection material is 4-8% of shape weight.
Moment connections — bolted flange plate, extended end plate, WUF-W (welded unreinforced flange, welded web) — carry substantially more material and fabrication labor. A W24×68 moment connection with bolted flange plates adds 140-180 lb of connection steel, 16-24 A325 bolts, and 4-6 hours of fab shop labor. Multiply across 60 moment connections on a four-story frame and you are looking at 10,000+ lb of unaccounted-for steel if you used a flat shear-connection factor.
"I lost a seven-story OMF project because I bid it like an IMF. The connection tonnage was 16% on the winning sheet and 9% on mine. Seven percent of 340 tons at $4,200 installed is the margin I gave away."
Gregory Huang, Senior Estimator, Keystone Steel Fabricators — Cleveland, OH
Bolts — A325 vs A490 and the count that gets skipped
A325 (now called Group A per AISC 360-22) bolts are the commodity. A490 (Group B) bolts are higher strength, used on moment connections, tension-heavy braces, and specific shear conditions. A490 bolts cost roughly 1.8x what A325 bolts cost, and they require stricter installation inspection — turn-of-nut procedure, tension calibration, or direct tension indicators.
Bolt count on a steel job runs 8-16 bolts per ton of structural shape for simple connections, and 20-32 bolts per ton on moment frames. At roughly $2.40 per A325 bolt delivered and $4.30 per A490, the bolt line item on a 300-ton frame is $15,000-$28,000 depending on mix. Most takeoffs aggregate it as "bolts and fasteners" with a flat $/ton allowance — which is fine until it is wrong by $10,000 on a moment-heavy job.
Shear studs — the composite deck multiplier
Composite floor decks require welded shear studs at the beam-to-concrete interface. Stud count is dictated by composite design — typically 3/4" diameter × 5" to 6" long, placed at 12-24" spacing along the top flange of each composite beam. A single 30-foot composite W18×35 beam carries 20-36 studs depending on design.
Studs run $1.40-$1.80 each material, plus welding labor in the shop or field at 0.06-0.10 hours per stud. On a 120,000 SF office building with composite framing across 4 floors, stud count can easily exceed 24,000. That is $36,000-$43,000 in stud material and 1,400-2,400 hours of stud welding — real scope, real money, and easy to miss if the estimator reads "composite deck" and moves on.
The misc metals carve-out
Stairs, handrails, ladders, roof screens, equipment supports, bollards, lintels, loose lintels over openings in CMU walls, channel frames for louvers, pipe bollards, dunnage for rooftop equipment — this is misc metals (Division 05 50 00). It lives on the architectural sheets more often than the structural ones, and it routinely gets carved out of the structural steel package or double-bid.
The tonnage is not huge — usually 5-10% of structural shape weight — but the labor hours per ton are 2-3x higher than structural because the pieces are smaller, the fabrication is more custom, and field install is one-off. Miscount 12 tons of misc metals at 90 labor hours per ton and you are 1,080 hours underbid. At a blended $95/hr, that is $102,000 gone.
The misc metals audit checklist
- Read the A-sheets for stair details, handrail runs, ladder calls, equipment screen elevations.
- Check spec section 05 50 00 for scope boundaries — structural vs architectural steel.
- Flag every non-wide-flange steel element on the S-sheets for inclusion in misc or exclusion by note.
- Cross-reference the mechanical equipment schedule for dunnage requirements.
- Loose lintels over CMU openings — on CMU-heavy jobs, this alone can be 2-3 tons.
Closing the gap
A disciplined steel takeoff produces shape tonnage from the member schedule, connection tonnage calculated per connection type (not flat), bolt count by grade, shear stud count by composite beam, and a separate misc metals tonnage with its own labor unit per ton. When these five numbers are built independently and then summed, the total tonnage lands within 2-3% of fabrication tickets. The 8-12% gap that sinks competitive bids disappears — not because it went away, but because it got counted.