Written notice before steel goes up
Under 29 CFR 1926.752(a), steel erection may not begin on new concrete footings, piers and walls until the steel erection contractor receives written notification that the concrete has reached either:
- 75 percent of its intended minimum compressive design strength, or
- sufficient strength to support the loads imposed during steel erection.
Verbal confirmation does not meet the rule; it must be written. Full 28-day design strength is not required, and 50 percent understates it. The figure is 75 percent.
Who gives the notice
The controlling contractor gives the written notification to the steel erection contractor before erection begins. The traps are the other parties who appear nearby:
- The structural engineer of record shows up in Subpart R for bolt equivalents and design matters, not as the party giving this notice.
- The erector's own competent person does not give it.
- The testing laboratory supplies the test results, but the notice itself comes from the controlling contractor to the erector.
How the 75 percent is measured
The rule bases the determination on an appropriate ASTM standard test method of field-cured samples. Each alternative fails for a specific reason:
- Laboratory-cured cylinders are not what the rule names; it says field-cured.
- Elapsed days alone are not a test of strength.
- A visual check by the erector's competent person is not an ASTM test.
Working the numbers
Multiply the specified design strength by 0.75.
- Footings specified at 4,000 psi: 0.75 × 4,000 psi = 3,000 psi minimum field-cured test strength before erection may start.
- 2,000 psi is only 50 percent, too low.
- 3,500 psi is 87.5 percent, which overstates the requirement.
- 4,000 psi is the full design strength, which the 75 percent test does not require.
Keep the three parts together: written notice, from the controlling contractor, showing 75 percent by ASTM field-cured tests (or strength sufficient for erection loads).