Commercial Building Inspector B2Structural SystemsEasy
A commercial building inspector is reviewing the structural plans for a new three-story office building. The plans indicate the use of concrete floor slabs. Which of the following is the minimum specified compressive strength (f'c) required for concrete in members not exposed to freeze-thaw cycles or sulfate attack, according to IBC 2021?
- A2,500 psi (17.2 MPa)
- B3,000 psi (20.7 MPa)
- C3,500 psi (24.1 MPa)
- D2,000 psi (13.8 MPa)
Show answer & explanationAnswer & explanation
Correct answer: A. 2,500 psi (17.2 MPa)
IBC 2021, Section 1905.1.1 refers to ACI 318-19, Section 19.2.1.1. For concrete not exposed to special conditions, the minimum specified compressive strength is 2,500 psi.
Why the other options are wrong
- B. This is a common strength used, but not the minimum required by code for general conditions.
- C. This strength is often used for higher performance or specific structural elements, exceeding the minimum for general use.
- D. This value is typically too low for structural concrete applications in commercial buildings.
Minimum Concrete f'c
The lowest acceptable specified compressive strength for structural concrete, as required by building codes for general conditions.
- Ensures adequate strength and durability.
- Varies based on exposure conditions (e.g., freeze-thaw, sulfate attack).
- For general structural use, IBC references ACI 318 minimums.
Memory trick: General Concrete needs a 'C' for Code-compliant strength.