Direct Answer
The most common field fit-up causes are: detailing errors (hole mislocations, wrong member length), fabrication errors (drilled wrong location, cut short), anchor bolt misplacement in concrete, and design coordination errors (member depth mismatch at connections). Out-of-tolerance concrete work is also a frequent culprit when base plates or embed plates don't land where the drawing shows.
Full Explanation
Fit-up problems are expensive because they occur in the field where labor rates are highest and crane time is running. Identifying the root cause is essential for both resolving the immediate problem and preventing recurrence. Common fit-up scenarios: (1) Beam is 3/4" too long — caused by fabrication error or design dimension error. (2) Column bolt holes don't align with beam holes — caused by detailing error in hole location or fabrication tolerance. (3) Column base plate won't seat on anchor bolts — caused by anchor bolt misplacement in concrete. (4) Moment connection flange won't clear — caused by section depth tolerance or weld reinforcement height.
What This Means for Your Shop
For each fit-up problem, your first step is to establish root cause before accepting any blame. Document the as-fabricated dimensions of the member in question and compare to the shop drawing. If your member matches the drawing, the error is elsewhere (detailing, design, or field work).
Common Mistakes
Field-modifying members (burning holes, cutting flanges) without engineering approval. Unauthorized field modifications can compromise structural integrity and create future inspection problems.
Recommended Process
When a fit-up problem occurs: (1) Stop. Do not attempt to force connections. (2) Document the condition with photos and measurements. (3) Submit an RFI to the engineer. (4) Wait for a formal resolution before proceeding. (5) Identify root cause and assign responsibility for cost.