Commercial Building Inspector B2Roof Ceiling ConstructionEasy
A structural engineer is designing a concrete roof slab for a commercial building. The slab is designed for a target 28-day compressive strength of 4,000 psi. According to ACI 318, what is the specified concrete compressive strength (f'c) typically used for structural concrete in the IBC?
- A3,000 psi
- B5,000 psi
- C4,000 psi
- D2,500 psi
Show answer & explanationAnswer & explanation
Correct answer: C. 4,000 psi
While ACI 318 allows for a range of concrete strengths, 4,000 psi (27.6 MPa) is a very common specified compressive strength (f'c) for structural concrete elements like roof slabs in commercial buildings, especially where moderate to heavy loads are anticipated.
Why the other options are wrong
- A. This strength is common for non-structural elements or lighter-duty applications, but 4,000 psi is more typical for structural slabs.
- B. While higher strengths are used, 4,000 psi is a more common baseline for general structural applications.
- D. This strength is generally considered too low for structural concrete roof slabs in commercial buildings.
Concrete Compressive Strength (f'c)
The specified compressive strength of concrete, typically measured at 28 days, which is a critical parameter for structural design.
- Measured in psi (pounds per square inch).
- Influences structural capacity.
- Specified by ACI 318 and referenced by IBC.
Memory trick: Strong concrete holds the load, a critical part of the building code.