Shop Drawings — Built for the Fabrication Floor
Shop drawings are fabrication documents. They tell the shop how to build each individual steel component — the length, section size, all hole locations with edge distances, bolt patterns, weld symbols, material grade, and surface preparation requirements. The primary user is the fabrication shop: layout workers, fitters, welders, and CNC machine operators. One shop drawing per unique piece mark.
Erection Drawings — Built for the Field
Erection drawings are field documents. They show where each piece mark goes in the completed structure — its grid location, elevation, orientation, and field connection requirements. Erection drawings are plan views and elevations that give the erection crew enough information to locate and orient each piece without measuring from the structural drawings. They include shipping marks, sequence numbers, and field bolt patterns.
How the Two Work Together
On an erection site, the superintendent uses erection drawings to direct the erection crew — 'Column C-104 goes at gridline D4, level 2 to 3.' The erection crew references erection drawings to set and plumb the piece. If there is a field fit question about how a specific connection goes together, the superintendent pulls the shop drawing for that piece mark to see the exact connection geometry. Both documents are necessary; neither replaces the other.
Content Differences in Detail
The content difference between a shop drawing and an erection drawing is more than just audience — it reflects a fundamental difference in purpose. A shop drawing for a W18x97 beam shows exact cut length, hole group spacing to 1/32", edge distances, weld size and length for each shop-welded plate, bolt diameter and grade, and material specification. An erection drawing for the same beam shows its grid location (B2-B3, level 2), its piece mark (B-0142), the field bolt pattern (4 — 7/8" A325 bolts each end), and a note pointing to the elevation drawing for the bay. The erection drawing contains no fabrication dimensions — those are irrelevant to the ironworker.
- Shop drawing: all dimensions to nearest 1/16", hole edge distances, weld symbols per AWS A2.4
- Erection drawing: grid location, elevation, orientation (N, S, E, W face for columns)
- Shop drawing: material grade on every member and plate
- Erection drawing: field bolt pattern and installation method only
- Shop drawing: surface preparation and coating zone callouts
- Erection drawing: erection sequence numbers, priority marks, shipping bundle reference
Approval Requirements for Each Document Type
Both shop drawings and erection drawings typically require EOR approval before fabrication and erection, respectively. The EOR's review of shop drawings focuses on structural compliance — connection types, member sizes, material grades. The review of erection drawings focuses on member location and orientation accuracy. Some EORs review both document types together in a single submittal; others prefer a separate submittal for erection drawings. Confirm the EOR's preference at kickoff to avoid a rejected submittal that slows the approval cycle.
What Happens When the Two Documents Conflict
Shop drawings and erection drawings are both extracted from the same 3D model in Tekla Structures — so conflicts between them should not exist. But they can arise when: a model is revised after the erection drawing was extracted but before the shop drawing was regenerated; or when a last-minute change is applied manually to one drawing type without updating the other. When a field crew finds a conflict between the erection drawing and the shop drawing for the same piece, work should stop until the discrepancy is resolved through the RFI process. Do not assume the erection drawing governs — or that the shop drawing governs. Both were generated from the same model and a conflict between them means the model had an error.
Phasing and Package Management
On phased projects, shop drawings and erection drawings for each release package should be issued together — not separately. An ironworker crew that receives erection drawings for Phase 1 but is still waiting for shop drawings on the same members cannot erect steel efficiently. Conversely, a shop that receives shop drawings for Phase 2 members cannot fabricate efficiently when the erection drawings for that phase have not been approved yet. Package definitions at project kickoff should specify which shop drawings and which erection drawings constitute each release package.