A residential structure in Honolulu requires a concrete slab foundation. Given a live load of 40 psf and dead load of 15 psf, what is the minimum required concrete compressive strength for the foundation according to Hawaii Building Code?
Correct Answer
A) 3,000 psi
For residential foundations in Hawaii, the minimum concrete compressive strength is typically 3,000 psi, which provides adequate strength for the given loads while considering local environmental conditions.
Why This Is the Correct Answer
3,000 psi is the standard minimum compressive strength for residential concrete foundations under Hawaii Building Code. This strength is sufficient for the combined load of 55 psf (40 + 15) while accounting for Hawaii's humid, salt-air environment that can degrade lower-strength mixes more rapidly.
Why the Other Options Are Wrong
Option B: 4,000 psi
4,000 psi exceeds the minimum requirement for standard residential foundations. While higher strength is used for commercial or marine-exposed structures in Hawaii, it is not the minimum code threshold for a typical residential slab under these load conditions.
Option C: 2,500 psi
2,500 psi is below the minimum threshold allowed by Hawaii Building Code for residential foundations. This strength is insufficient to resist the combined loading and the environmental degradation common in Hawaii's climate.
Option D: 3,500 psi
3,500 psi is stronger than the code minimum but is not the correct minimum requirement. Confusing the minimum with a commonly specified value is a frequent test error.
Memory Technique
Remember '3 for residential' — 3,000 psi is the floor for residential foundations in Hawaii. Higher strengths (4,000+) are reserved for marine, commercial, or post-tensioned applications.
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