Joists at columns: the 60 ft line
29 CFR 1926.757(a) splits joists at or near columns by span.
- 60 ft or less, 1926.757(a)(3): the joist must be designed so one employee can release the hoisting cable without the need for erection bridging. A 55 ft joist falls here, so no row of bridging is required before release.
- More than 60 ft, 1926.757(a)(4): the joist must be set in tandem with all bridging installed.
Trap: keeping cables attached until all bridging is installed is the rule for spans over 100 ft through 144 ft in 1926.757(d), not for joists at columns.
The only alternative to tandem setting
For a joist at a column over 60 ft, such as a 64 ft span, 1926.757(a)(4) allows one alternative: an alternative method of erection designed by a qualified person, giving equivalent stability, and included in the site-specific erection plan.
All three elements are needed. These fail:
- A competent person's approval on the day of erection.
- Verbal approval from the engineer, which is not a qualified-person design in the erection plan.
- A single midspan row of bridging.
End attachments by joist series
1926.757(b) sets minimum end attachments. The exam swaps the two sets.
- K-series: at least two 1/8 in fillet welds 1 in long, or two 1/2 in bolts, or the equivalent.
- LH and DLH series and joist girders: at least two 1/4 in fillet welds 2 in long, or two 3/4 in bolts, or the equivalent.
Common swaps
- A DLH joist bolted with two 1/2 in bolts fails; that is the K-series figure. One 3/4 in bolt is half the count, and two 5/8 in bolts are undersized. The answer is two 3/4 in bolts.
- A K-series joist welded with two 1/8 in fillet welds 3/4 in long fails, because the welds must be 1 in long. The rule sets a length, so the length matters for K-series as well as for LH and DLH.