Commercial Building Inspector B2Footings and FoundationsMedium
An inspector is observing the placement of anchor bolts for a steel column base plate in a commercial building. The plans specify a 3/4-inch diameter anchor bolt. According to the 2021 IBC, what is the minimum concrete embedment depth required for a 3/4-inch diameter anchor bolt in normal-weight concrete, assuming no special conditions or seismic design factors that would require greater embedment?
- A5 inches
- B8 inches
- C7 inches
- D4 inches
Show answer & explanationAnswer & explanation
Correct answer: C. 7 inches
IBC Section 1905.1.8 and ACI 318 (referenced by IBC) provide embedment requirements for anchor bolts. For a 3/4-inch diameter anchor bolt in normal-weight concrete, the minimum effective embedment depth (hef) is typically 7 inches, as derived from ACI 318 Table 17.5.2.2.1a (or similar provisions for cast-in anchors).
Why the other options are wrong
- A. 5 inches is also typically too shallow for a 3/4-inch anchor bolt.
- B. 8 inches is a safe depth but not the minimum required by code for this specific bolt diameter.
- D. 4 inches is generally insufficient for a 3/4-inch diameter anchor bolt to develop adequate pullout strength.
Anchor Bolt Embedment Depth
The minimum depth an anchor bolt must be embedded into concrete to ensure sufficient pull-out and shear strength.
- Critical for transferring loads from steel to concrete.
- Depends on bolt diameter, concrete strength, and load type.
- Governed by ACI 318, referenced by IBC.
Memory trick: Deep bolts hold tight, preventing columns from taking flight.