Tolerance Dispute at Panel-to-Foundation Connection
You are the QA lead on a tilt-up warehouse. The foundation contractor set anchor bolts for the panel base connections. Survey of 30 bolts shows 9 are outside the ±1/4 in. tolerance in plan, with the worst at 5/8 in. off. The panels are cast and ready to lift. The structural drawings show a slotted base plate with 1/2 in. of adjustment in one direction and a welded shear lug. The panel erector says the slots will absorb the error. The engineer of record has not been consulted. The foundation contractor wants to sign off the bolts as acceptable.
1. Is the erector correct that the slots absorb the error? Walk through the check.
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Not necessarily. The slot provides 1/2 in. of adjustment in one direction, but that is total movement, so the bolt can move ±1/4 in. from the nominal position within the slot. A bolt that is 5/8 in. off in the slotted direction exceeds the slot's ability to accommodate it, and a bolt that is off in the non-slotted direction has no adjustment at all.
The check must be done per bolt and per direction:
- Resolve each bolt's offset into the slotted and non-slotted directions.
- Compare the slotted-direction offset to the slot's ±1/4 in. capacity and the non-slotted-direction offset to the plate's hole clearance.
- Any bolt exceeding either is non-conforming.
With 9 of 30 out of tolerance and a worst case of 5/8 in., several bolts will not fit within the slot. The erector's blanket statement is not an engineering evaluation. The shear lug also matters: if the lug must bear on the concrete, its position relative to the bolt and the pocket affects whether the connection can develop shear.
2. What is the correct disposition process, and what are the possible outcomes?
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Process:
- Do not sign off the bolts as acceptable. Document the survey with bolt-by-bolt offsets in both directions.
- Notify the engineer of record in writing with the survey and the plate/slot geometry, and request a disposition for each non-conforming bolt.
- Hold panel erection for the affected locations until the disposition is issued, or erect only locations confirmed conforming.
Possible outcomes from the engineer:
- Accept bolts within the slot's actual capacity after a per-bolt check (some of the 9 may be acceptable).
- Enlarge or slot the base plate per an engineer detail, with weld or plate reinforcement as required.
- Relocate or re-set the bolt by drilling and epoxying a new anchor per engineer design, or by chipping and recasting the pocket.
- Modify the shear lug or add a supplemental connection.
Record the disposition, the repair, and the inspection of the repair. The foundation contractor cannot self-accept a tolerance deviation; the engineer of record owns that decision.