Structural Steel Detailing
Structural Steel Bill of Materials: A Practical Guide for Detailers
How to build a structural steel bill of materials that purchasing, the shop and the field can all trust — including marks, grades, lengths and bolts.
A bill of materials is not a spreadsheet souvenir of the model. It is the purchasing and cutting list. If the BOM is wrong, the drawing can be right and the project will still buy the wrong length or the wrong grade. Treat the BOM as a controlled drawing, with a revision letter of its own.
This guide covers what to include, how to reconcile quantities, and how bolts and miscellaneous plates get lost. For spreadsheet-heavy teams, StruTools Excel programs are aimed at this kind of structured engineering table work.
Reconcile the BOM against plans using the same marks you used on fabrication drawings. Never maintain a parallel nicknaming system in Excel.
What a usable steel BOM contains
- Piece or shipping mark
- Quantity
- Section or plate size
- Grade / specification
- Length or plate dimensions, including extra for camber or mill tolerance if your shop standard requires it
- Weight if the contract or shipping needs it, with the calculation basis stated
- Finish (paint, galvanize, prime, none)
- Remarks: camber, shop assembly, hold
Main steel versus miscellaneous versus bolts
Lumping everything into one unsorted list is how clip angles and bolts disappear. Split, at least, into main members, connection material, deck support / miscellaneous, and fasteners. Bolts need diameter, grade, length, hole type if it affects purchasing, and whether they are shop or field.
| List | Typical rows | Common miss |
|---|---|---|
| Main members | Columns, rafters, beams, braces | Mirrored marks counted once |
| Plates & connections | Base plates, end plates, gussets, clips | Typical “4 off” never multiplied |
| Fasteners | Bolts, nuts, washers, anchors | Field bolts omitted because they are “the erector’s problem” |
| Finish extras | Vent holes, tags, extra primer | Not listed, then not done |
Reconciliation is the real quality control
Exporting a BOM from a model is a start. Checking it is the work. Count columns on the plan. Count rafters by bay. Search for marks that exist only in Excel or only on the drawing. Typical notes that say “similar about ridge” must be expanded into quantities, not left as a comment.
Revision control for lists
When a rafter length changes, the drawing, the BOM and the mill order must change together. Issue the BOM with a revision letter and a short description: “Rev C — added 4 FB- bracing, lengthened R12.” Purchasing should not have to diff unmarked spreadsheets.
Weights and estimates
If you report weights, state whether they are theoretical, with or without connection material, and whether paint or bolts are included. Do not present a rough estimate as a weighing-scale fact. Downstream shipping and quotations will treat your number as exact.
A practical workflow
- Freeze marks on the drawings.
- Export or compile the BOM from the same source files.
- Split lists (main, misc, bolts).
- Reconcile counts against plans.
- Issue with a revision letter and send with the drawing transmittal.
Engineering tips
- One mark system only. Excel nicknames are how pieces get double-ordered.
- Keep bolt lists in piece-mark order so the field can find them.
- If you automate extraction, still spot-check one bay by hand.
Common mistakes
Letting purchasing edit the live BOM
They need a copy. The live list stays with detailing so revisions stay coherent.
Mixing metres and millimetres in one column
State units in the header. Mixed units are silent length errors.
Dropping connection material because it is “in the typical”
Purchasing cannot order a typical detail. They order plates with sizes.
Checklist
- Marks match drawings
- Quantities reconciled to plans
- Grades filled
- Lengths/plate sizes filled
- Finish column complete
- Bolts split shop/field
- Holds flagged, not deleted
- Revision letter on the list
Frequently asked questions
Should the BOM be on the drawings?
A summary can be. Long lists are easier as controlled schedules. Either way they share marks and revisions with the sheets.
Who owns bolt quantities?
Whoever the contract says supplies them. If the fabricator supplies field bolts, they belong on the BOM even though they are used on site.
Can I maintain the BOM only in the 3D model?
Yes if the issued report is revision-controlled and reviewers/purchasing can open it. A model that only one person can query is not an issued BOM.
How does this relate to Excel tools?
Excel is fine for sorting, filters and checks. It becomes dangerous when it is an uncontrolled parallel model. Use it as a view of the controlled list.
Where this leaves the work
If drawings, BOM and mill order tell three different stories, fabrication will believe the mill order. Make the BOM boring, current and reconcilable.
Use the detailing checklist issue-control items whenever the BOM changes, even if “no sheets were redrawn.”
This article provides general educational information. Project-specific structural design, calculations and drawings should be reviewed by appropriately qualified engineering professionals and checked against applicable project requirements and standards. StruTools does not replace engineering judgement or professional design review.