Direct Answer
Dimensional inspection verifies that each fabricated member matches its piece mark drawing to within specified tolerances (AISC Code of Standard Practice Chapter 6 and Appendix 6). Key measurements: overall length (±1/16" for beams), hole locations (±1/32" from theoretical position, ±3/16" from piece end), cope dimensions, and connection plate location and orientation. Inspection is performed with a steel tape, bolt gauge, and square before the member leaves the shop.
Full Explanation
AISC tolerances for structural members: overall length tolerance is ±1/8" for columns and ±3/16" for beams up to 30 feet (increasing slightly for longer members). Hole location tolerance within a bolt group is ±1/32". End squareness (perpendicularity of the cut end to the member axis) is limited. Connection plate position tolerance (vertical and horizontal) is ±3/16". These tolerances stack — a member at the limit of every tolerance simultaneously can still cause field fit-up problems, especially with pretensioned bolt groups.
What This Means for Your Shop
Dimensional inspection must happen before blasting and painting — paint conceals defects and makes rework more expensive. Establish inspection hold points between assembly and surface preparation in your production flow.
Common Mistakes
Performing dimensional inspection only on complex assemblies, skipping routine beams as 'standard.' Errors on routine members are just as disruptive as errors on complex ones.
Recommended Process
Implement a tiered inspection approach: every member gets a minimum check (length, hole pattern at each end), complex assemblies get a full dimensional inspection. Record results on a standardized form, signed by the inspector. Retain records in the project file.