What is the minimum concrete compressive strength required for structural concrete in residential construction according to CBC?
Correct Answer
A) 2,500 psi
CBC requires minimum 2,500 psi compressive strength for structural concrete in residential applications, with higher strengths required for specific conditions or seismic zones.
Why This Is the Correct Answer
The California Building Code (CBC), following ACI 318 provisions, sets the minimum specified compressive strength (f'c) for structural concrete in residential construction at 2,500 psi. This baseline ensures adequate load-bearing capacity under typical residential conditions. Higher strengths (3,000–4,000 psi or more) are required for specific applications such as foundations in high-sulfate soils, seismic zones, or exposure to freezing and thawing.
Why the Other Options Are Wrong
Option B: 3,000 psi
3,000 psi is a common concrete mix used in residential footings and slabs and may be specified by engineers for better durability, but it is not the CBC minimum for general structural residential use. Confusing a typical or recommended practice with the code minimum is a common error.
Option C: 2,000 psi
2,000 psi is below the CBC minimum and would not provide adequate structural performance for most residential applications. While 2,000 psi concrete exists commercially, it is not an acceptable minimum for structural members under CBC.
Option D: 4,000 psi
4,000 psi is required for specific high-demand conditions — including concrete exposed to seawater, deicing chemicals, or moderate-to-severe sulfate environments — but it is not the base minimum for standard residential structural concrete. Applying a high-exposure requirement to all residential construction would be over-conservative and is not what CBC mandates.
Memory Technique
Remember '2,500 is the minimum to pass' — just like you need a minimum score to pass the exam, concrete needs 2,500 psi minimum to qualify under CBC. Anything stronger is a bonus.
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You are reviewing plans for a mixed-use building where the ground floor will house a restaurant with commercial kitchen equipment. The architect has specified standard residential electrical requirements throughout. What Title 24 compliance issue should you identify?
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A wood frame shear wall is 20 feet long and must resist 8,000 pounds of lateral force. Using 15/32" structural sheathing with 8d nails at 6" o.c., what is the unit shear?