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RE: 3000 psi concrete and special inspection

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Title: RE: 3000 psi concrete and special inspection

Dennis,

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  

   

Steve,

Are you speaking of the exception 2 of section 1701.5? If so this refers

to the need to take test specimens not whether or not the minimum

compressive strength is limited to 2,500 or 3,000 psi. I agree there is

an implication here, but you should take the lead from section 1921 and

section 1922 that refers more to specifically to lateral resisting

structural concrete or plan structural concrete.

Interestingly, I would probably take the lead on this from the

Prescriptive codes in Section 2320. My thinking here is that if section

1921 governed all concrete except footings, then no home could be

constructed prescriptively in section 2320 as the idea that the

foundation required special inspection and observation takes it out of

the realm of Conventional Construction. How's this for a reach?

--

*Dennis S. Wish, PE*

*California Professional Engineer

Structural Engineering Consultant



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