Four anchor rods per column
Under 29 CFR 1926.755(a)(1), all columns must be anchored by a minimum of 4 anchor rods (anchor bolts). Two is the minimum bolts per solid web connection under 1926.756(a)(1), not the rod count, and three and six are not Subpart R minimums. A common error is looking for the 4-rod rule in 1926.756; it is in 1926.755.
The rule reaches columns as defined in 1926.751, and that definition excludes posts weighing less than 300 lb. So a light post is outside the 4-rod minimum. Everything else stays a column:
- a perimeter column (1926.756(e) adds height and cable-hole rules),
- a column supporting steel joists (it may also need the stabilizer plate in 1926.757(a)(1)(i)),
- a column that will be spliced (the splice must meet 1926.756(d)).
The 300 lb at 18 in load
Under 1926.755(a)(2), each column anchor rod assembly, including the column-to-base plate weld and the foundation, must resist a minimum eccentric gravity load of 300 lb (136.2 kg) located 18 in (0.46 m) from the extreme outer face of the column in each direction at the top of the column shaft.
1926.756(d) applies the same 300 lb at 18 in load to each column splice. Thinking it applies only to splices, or only to anchorage, is a common error: it applies to both. Relying only on permanent design loads is wrong, because the rule sets a minimum erection load.
Look-alike figures that do not belong here: 42 in (perimeter cable height, 1926.756(e)), 1,000 lb (bridging bundle, 1926.757(e)(3)), 4,000 lb (decking bundle) and the 1 ft load placement rule (1926.757(e)), and twice the load on the cover (opening covers, 1926.754(e)(3)).
Anchor rod repairs and changes
Anchor rods may not be repaired, replaced or field-modified without approval of the project structural engineer of record, 1926.755(b)(1). The controlling contractor must notify the erector in writing before the column is erected, (b)(2).
The traps: a competent person's approval and verbal notice meet neither requirement, the erector's foreman has no approval authority, and a like-for-like replacement is still a replacement that needs the engineer's approval.