Direct Answer
A bill of materials (BOM) is a complete, itemized list of every steel member, plate, bolt, and hardware item needed to fabricate and erect the structure. A good BOM includes piece mark, quantity, description, section size, material grade, length, finish, and weight — everything the purchasing agent needs to order material and the shop floor needs to track production.
Full Explanation
BOMs are generated directly from the 3D detailing model, which ensures that quantities are accurate and match the drawings. The BOM is organized by piece mark or by assembly, and often sorted by material type for procurement efficiency. In Tekla Structures, the BOM is a live document — any change to the model updates the BOM automatically. A BOM exported from the model is far more reliable than a manually prepared material list.
What This Means for Your Shop
Your material purchasing should come from the model-generated BOM, not from a manual takeoff of the design drawings. Model-generated BOMs reduce over-ordering by 5–15% on average and catch missing members that manual takeoffs miss.
Common Mistakes
Using the BOM from a preliminary model (before all connections are designed) to order material. Connection plates, stiffeners, and gussets often add 8–15% to the total weight and are absent from early BOMs.
Recommended Process
Order long-lead structural shapes early from a preliminary BOM. Wait for the fully detailed, connection-complete model BOM before ordering plates, clips, and miscellaneous hardware. Maintain a living BOM that is updated with every model revision.