Required BOM Fields
- Piece mark — unique member identifier linking the BOM to the drawing set
- Description — member type and orientation (e.g., W14×132 column, HSS 8×8×1/2 tube brace)
- Section size and standard — W14×132 ASTM A992, L4×4×5/16 A36, PL1×12 A572-50
- Material grade — governs mill certificate requirements and welding procedure selection
- Quantity — number of identical members at this piece mark
- Length — finished length of each member after cutting
- Unit weight and total weight — for shipping, erection planning, and cost verification
- Piece mark drawing reference — the drawing sheet from which this entry was generated
- Package or release assignment — which fabrication release this member belongs to
BOM Accuracy and the Mill Order
The fabricator's mill order is placed from the BOM — or from a preliminary material list derived from the BOM. An inaccurate BOM leads to wrong quantities ordered, wrong grades specified, or wrong lengths purchased. Each of these errors costs money: surplus material must be returned or scrapped, short orders require emergency purchases at spot pricing, and wrong grades require material testing or replacement.
Preliminary vs. Final BOM
A preliminary material list is issued before connection details are finalized — it provides section sizes and approximate member lengths sufficient to place mill orders on long-lead items. The final BOM is issued with the approved shop drawings and includes exact lengths, connection plate counts, and hardware quantities. The fabricator should confirm which version is current before placing any purchase order.
Connection Material in the BOM
Connection material — shear tabs, end plates, gusset plates, stiffeners, and connection angles — should appear in the BOM as individual line items, not as a lump 'connection material' allowance. Each plate should have a piece mark, a size, a material grade, and a quantity. This level of detail allows the purchasing department to place precise plate orders rather than guessing quantities, and it allows the fabricator to track connection material usage against the BOM during production. Tekla Structures generates connection material automatically in the BOM if all connection components are modeled as real objects.
Bolt Lists and Hardware in the BOM
A complete structural steel BOM includes bolt lists — the count of every bolt diameter, grade, length, and installation type required for the project. Bolt quantities should be broken out by shop bolts (installed in the fabrication shop) and field bolts (installed during erection) because these are purchased separately and handled differently. A bolt list generated from the Tekla model counts every bolt in every connection; a manually prepared bolt list is subject to counting errors that result in short orders. Hardware items — anchor rods, leveling nuts, shim packs, and construction shims — should also appear as BOM line items.
- Shop bolts — diameter, grade, length, and installation type for shop-installed connections
- Field bolts — same data, flagged for field installation
- Anchor rods — diameter, length, ASTM grade (F1554 grade specified), thread length, and nut and washer requirements
- Leveling nuts and shim packs — quantities by column base plate
- Erection pins and temporary bolts — if specified for erection sequence
Using the BOM for Cost Verification and Reconciliation
At project award, the fabricator's estimating BOM (built from design drawings) and the detailer's final BOM (built from the model) should be reconciled. Differences reveal scope additions or deletions that occurred during the design-to-detailing transition. Significant differences — more than 5% by tonnage — should be investigated and explained before invoicing. At project closeout, a final BOM reconciliation against actual material used identifies any over-order or under-order that affects the project's material cost accounting. Tekla's BOM report can be filtered by release package, making this reconciliation tractable even on large projects.