Edge Distance Conflict Discovered After Layout
You are inspecting adhesive anchors for a steel ledger attached to the face of a concrete curb wall. The approved design shows anchors with a specified edge distance to the top of the curb. During layout verification, you find that the as-built curb is 1-1/2 inches narrower at the top than shown on the drawings (the forming was adjusted in the field), so the actual edge distance to the top face is about 1 inch less than the design value for the row of anchors nearest the top. The holes for that row have already been drilled and two anchors set. The manufacturer's published tables include minimum edge distance and show that capacity decreases as edge distance decreases; the design did not include supplementary edge reinforcement. The contractor wants to proceed with the remaining anchors 'because the adhesive is strong.'
1. What is the significance of the reduced edge distance, and what should happen before any more anchors are installed?
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Reduced edge distance is a capacity and failure-mode issue, not a cosmetic one.
- The manufacturer's tables are based on a minimum edge distance; below it, the concrete breakout/edge failure mode can govern and the tabulated tension capacity no longer applies. The design edge distance was part of the basis of the approved submittal.
- The as-built condition (≈1 in. less than design, no supplementary edge reinforcement) falls outside that basis. 'Strong adhesive' does not compensate - the limiting failure may be concrete edge breakout, which adhesive strength cannot fix.
- Before more anchors: stop installation in the affected row, document the as-built edge distance with measurements, and route to the EOR/manufacturer for evaluation. Possible outcomes: relocate the anchor row, reduce load, add edge reinforcement or a different anchorage, or obtain written engineered acceptance with reduced capacity. The inspector must not approve the reduced edge distance in the field.
- The two already-set anchors are also affected and must be included in the evaluation.
2. How would you verify and document the as-built edge distance and the disposition of the affected anchors?
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- Measurement: measure edge distance from the center of each hole/anchor to the actual concrete edge, not to the drawing line, at the top face; record each value individually rather than a single nominal number. Note the as-built curb dimension and the field change that caused it.
- Comparison: compare against the manufacturer's published minimum edge distance and the design value; identify exactly which anchors fall below the minimum and by how much.
- Disposition record: document the nonconformance, the EOR/manufacturer response, and the accepted resolution (relocation, added reinforcement, reduced capacity, replacement). Mark affected anchors on the as-built layout.
- Hold point: no further drilling or setting in the affected row until the disposition is in writing; re-verify layout of relocated anchors for spacing and edge distance before drilling.
- Report: include the field change to the curb, the measured edge distances, and the resolution in the inspection report so the record shows the deviation was evaluated, not ignored.