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Re: 3000 psi concrete and special inspection

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S. Gordin wrote:


As always - great analysis and insight.
Here are two more cents.

First, it is not just specimens, but the [continuous, per 1701.6.1] inspection during concrete placement. Furthermore, the special inspection per Section 1701.5.1 is also referenced in 1701.5.4.2 (reinforcing steel has to be inspected if inspection per 1701.5.1 is required). Second, as far as the 3,000 PSI requirements, I would refer to Sections 1921.2.1.5 and, especially, 1921.2.4.1:

"Compressive strength... of [concrete in members resisting earthquake-induced forces]... shall not be less than 3000 PSI. Exception: footings of buildings three stories or less may have concrete with f'c of not less than 2500 PSI."

Third, strictly speaking, any formal, to-the-letter, interpretation of Section 1921.2.1 would necessarily include walkways and patios into the "Scope" requiring 3,000 PSI concrete...

I agree with Stan Scholl - 2,500 PSI is what I've seen in 90% of the projects I had to review. And 2500 PSI still was an overkill in most of those, even for concrete retaining walls. In grade beams and drilled CIP piles - I do not specify anything below 3,000 PSI. Steve Gordin

I disagree as I think you missed the section on structural plain concrete. Please refer to section 1922 and again specifically 1922.2.4.1 which states similar reference as section 1921 but deals with foundations and slab on grades. FWIW, I know of no city that requires the use of 3,000 psi in Southern California for a slab on grade or a residential (up to three stories) continuous foundation or pad footings. The only time this becomes an issue is when there is a moment frame, embedded column or other lateral load resisting element on an isolated foundation such as a grade beam.

Reread this section to see the difference - it could never be applicable to flatwork or most of us are really in trouble.



*Dennis S. Wish, PE*
*California Professional Engineer
Structural Engineering Consultant

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