Direct Answer
When a section is unavailable or has excessive lead time, options include: substituting an equivalent or heavier section with engineer approval, sourcing from an alternative service center or steel distribution network, using a built-up (fabricated) section that approximates the required properties, or adjusting the project schedule to accommodate the lead time. Always involve the engineer in any section substitution — substitutions require engineering approval even if the substitute is 'stronger.'
Full Explanation
Substitution process: (1) Identify the unavailable section and its structural requirements (Sx, Ix, weight, depth). (2) Find candidate substitutes from available inventory (same or heavier weight in same nominal depth family). (3) Submit an RFI to the engineer proposing the substitution with the substitute's section properties. (4) Engineer evaluates and approves or rejects. (5) If approved, update the BOM, detailing model, and shop drawings. Common substitutions: W14×90 for W14×82 (heavier weight, similar depth), built-up web-and-flange plate girder to replace unavailable deep W-shape.
What This Means for Your Shop
In tight markets, section availability can change from 'yes' to 'no' between your order and delivery. Include a materials availability clause in your subcontract that protects you from cost increases if standard sections become unavailable after contract signing.
Common Mistakes
Self-approving a 'heavier is always better' substitution without engineering review. A deeper section might conflict with architectural constraints; a heavier section might impose higher loads on supporting members that aren't designed for the increase.
Recommended Process
Establish a relationship with 2–3 service centers so you can quickly check availability across multiple sources. Develop a standard RFI template for section substitution proposals that includes a comparison table of structural properties. Submit quickly to maintain schedule.