The member schedule is not the fabrication ticket
A structural steel takeoff that reads W14×90 off the column schedule, multiplies 90 lb/ft by the column length, and calls it tonnage has produced a member weight. The fabricator sees something very different. For every column there is a base plate and cap plate. For every beam-to-column connection there is a shear tab or a moment end plate. For every brace there is a gusset, a stem plate, and erection fills. None of these show up on the member schedule. All of them show up on the bill of lading.
AISC 360-22 Chapter J governs connection design. It defines simple shear connections (Type SSC), fully restrained moment connections (Type FR), and partially restrained (Type PR). Every connection type brings its own plate family and its own weight.
The 8-12% number — where it comes from
RSMeans Building Construction Cost Data 2025, Division 05 12 23, notes that "connection materials typically add 8-10% to main member weight for shop fabrication." AISC Steel Construction Manual, 16th Ed., Part 7 design examples imply comparable ratios. MBMA Metal Building Systems Manual documents a slightly lower 5-7% range for pre-engineered buildings where connections are simpler and standardized. Fabricator shop data from a sample of six mid-size US mills over 2022-2025 showed connection weight as a percentage of member weight ranging from 7.8% (simple braced frame, low-rise office) to 14.1% (moment frame hospital with seismic detailing).
Wtotal = Wmembers · (1 + αconn)where αconn ≈ 0.08–0.12 (typical) and 0.13–0.16 (SMF/seismic)
Connection types and their weight signatures
| Connection Type | Per-Conn Weight | Freq. per ton | Tonnage Adder |
|---|---|---|---|
| Shear tab (simple shear) | 8–18 lb | 8–12 | 3–4% |
| Double-angle clip | 14–26 lb | 6–10 | 3–5% |
| Bolted end-plate moment | 45–120 lb | 2–4 | 2–4% |
| Welded direct moment (WUF) | 30–70 lb (stiffeners) | 2–4 | 1–2% |
| Gusset (braced frame) | 35–180 lb | 1–3 | 1–3% |
| Col. stiffener/continuity pl | 18–55 lb | 3–6 | 1–2% |
| Col. base plate | 40–420 lb | ~0.4 | 0.8–1.5% |
| Col. cap plate | 25–90 lb | ~0.4 | 0.3–0.6% |
Source: aggregated fabricator shop data (2022-2025) cross-checked against AISC Manual Part 10 tables and AISC Design Guide 29 (vertical bracing). The right-hand column assumes an average 40 lb/ft member weight profile; actual tonnage adders scale with the structure type.
Shear tabs: the most overlooked plate in the scope
A typical shear tab is 3/8" PL × 4" × 9" with three 3/4" A325 bolts. That is roughly 14 lbs of plate per connection. On a mid-rise office with 22 beam-to-column connections per floor and 12 floors, that is 264 connections, or 3,696 lbs — 1.85 tons just in shear tabs on a 100-ton package. Include the bolts (3/4" A325 heavy-hex at ~0.31 lb each), nuts, and washers and you add another 260 lbs per floor.
AISC Steel Construction Manual Table 10-9 provides pre-designed shear tab configurations by bolt count. Pulling weights directly from this table and multiplying by connection count is the fastest defensible way to carry shear tabs. Do not rely on a generic percentage.
Gussets and the braced-frame premium
A gusset plate at a braced-frame work point can be 1/2″ or 3/4″ PL depending on the brace force. A typical concentric-braced-frame gusset on an HSS6×6×1/2 brace is about 22″ × 28″ × 5/8″ thick — roughly 110 lbs per gusset. On an SCBF or BRBF system (AISC 341-22 §F2, §F4) the gusset design per the Uniform Force Method or the work-point offset method can drive thicknesses up to 1″ and dimensions above 36″, putting individual gussets over 300 lbs.
A lateral system with 48 brace work points (12 frames, 4 levels) at an average 140 lbs/gusset is 6,720 lbs — 3.36 tons of gusset alone, before stiffeners or stem plates.
Taking "8% connection adder" on a seismic moment-frame job
An 8% adder is right for a braced low-rise. Apply it to an SMF hospital with RBS beams, continuity plates, doubler plates, and column web stiffeners per AISC 341-22 §E3 and you will be 4-6% light. SMF detailing routinely runs 14-16% connection weight. A 600-ton hospital frame at the wrong adder is 30-40 tons of missing plate — roughly $125,000-$170,000 at current material-plus-install rates.
Stiffeners, doublers, and continuity plates
AISC 341-22 §E3.6f requires column web doubler plates and continuity plates at moment connections when the panel zone or web local yielding check fails. These are rarely shown on S-sheet column schedules — they appear on connection detail sheets or are left to the connection designer. On a moment-frame job:
- Continuity plates match beam flange thickness, typically 1/2" to 3/4" at typical office spans. Two per beam connection (top and bottom flange).
- Doubler plates vary from 1/4" to 1-1/4" on heavy SMF; often 3/8"-1/2" on typical commercial.
- Web stiffeners at loads (girder reactions into columns) — check AISC 360-22 §J10.
Base plates and anchor rod packages
Column base plates by themselves are not small. A W14×90 column under a 3-story office typically sits on a 20″×20″×1-1/2″ PL, roughly 212 lbs. Heavy warehouse or crane columns can see 30″×30″×3″ plates at 750+ lbs each. On 42 columns in an office frame that is ~8,900 lbs — 4.45 tons of base plate not usually counted in the member schedule.
Anchor rod assemblies per ASTM F1554 are separate but often in the steel bid scope. F1554 Gr. 55 rods at 1″ diameter are ~2.67 lb/ft; at 36″ embedment plus projection and template, four rods per column on 42 columns is roughly 560 lbs of rod, plus template steel, sleeve couplers (if any), and washer assemblies.
"Young estimators want one number — the connection percentage. Senior estimators carry shear tabs by Table 10-9 count, moment connections by detail, gussets by brace elevation, continuity and doublers by AISC 341 check. The percentage is the cover story, not the math."
Harlan Voyles, Chief Estimator, Keystone Iron & Steel — Cleveland, OH
Bolted vs. welded: the labor delta
Beyond tonnage, connection type drives labor hours. AISC Code of Standard Practice §3.1.2 makes connection design the fabricator's responsibility unless otherwise noted, but the detail type is almost always set by the engineer. Typical install labor:
| Connection Method | Shop hrs / conn | Field hrs / conn | Notes |
|---|---|---|---|
| Bolted shear tab, 3-bolt | 0.45 | 0.20 | Fastest field install |
| Bolted end-plate moment | 1.10 | 0.45 | Heavy A490-TC bolts typical |
| Welded direct moment (WUF-W) | 0.85 | 2.50–3.20 | CJP welds, field CWI-inspected |
| Gusset, bolted | 1.40 | 0.55 | Heavier plate, more holes |
| Gusset, welded | 0.95 | 1.80 | Field welds to beam/column |
Source: AISC Steel Solutions Center field labor data and erector productivity reports 2023-2024. The field-hour differential between bolted and welded moment connections is roughly 5-7×. On a 200-connection moment frame, the decision between WUF-W and bolted end-plate changes the field labor budget by 400-500 hours — roughly $28,000-$40,000 at typical Ironworkers Local rates plus burden.
Erector vs. fabricator responsibility split
AISC Code of Standard Practice §7.10 is the line most bids get wrong. Shop connections (welds, bolts installed at the fabrication shop) are fabricator scope. Field connections (bolts installed after erection, field welds) are erector scope. Loose shipping material, temporary erection bolts, drift pins — these belong to the erector. When a connection detail calls for "3 A325 bolts field-installed, 3 additional A325 bolts shop-installed for member handling," missing the shop-installed bolt count hands $400–$800 of material per connection to whichever contractor absorbed it, depending on how the scope was written.
What a defensible connection takeoff contains
- Connection count by type (shear tab, double-angle, bolted end-plate, WUF, gusset, splice) extracted from connection details.
- Per-connection plate weight from AISC Manual tables or connection detail plates.
- Continuity and doubler plate count from moment-frame and braced-frame detail sheets.
- Base plate and cap plate weights by column type.
- Bolt count by grade (A325 / A490 / F3125), diameter, and length.
- Anchor rod package per F1554 with grade, diameter, embedment.
- Shop labor hours by connection type.
- Field labor hours by connection type, separated between erector bolt-up and erector field welding.
- Field weld inventory (CJP, PJP, fillet) with linear inches for CWI inspection budget.
PILRS extracts connection details and base plate schedules alongside member schedules so the tonnage number reflects everything that will show up on the fabricator's ticket. See PILRS pricing and let the next steel package be the one where the fabrication ticket matches the bid.