RE: bar spacing

Yes, in FL it is very common to find hollow 8” CMU with 1-#5 @ 6 to 8’ o.c. in the 110/120B and 16”o.c. in Miami.  So how is it possible that solid concrete can’t do as well or better?  Like I said before, try working out your conservative assumptions and remember that you still have a fairly large FOS working on your side and see if you can’t get comfortable with it.  Personally, I think 48” o.c. isn’t unreasonable.

 

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From: Jordan Truesdell, PE [mailto:seaint2@truesdellengineering.com]
Sent: Friday, September 04, 2009 8:08 AM
To: seaint@seaint.org
Subject: Re: bar spacing

 

I always find discussions like this interesting, especially since CMU is regularly reinforced vertically at 48" o/c with nary a second thought, and in seismic A & B horizontal reinforcement is allowed at 10' o/c. 

This discussion is somewhat timely, as I just had a contractor call me on a failed rebar inspection. Took me two hours to figure out WHY he failed. There were about three or four issues. Everything seemed to work fine for residential prescriptive codes save bar placement - and they had proportionally more steel than necessary for the actual "d" compared to the code tables. What got them was that this was a 4 unit apartment so their planned us of ACI332 and the IRC (this a residential builder) torpedoed them.  The horizontal bars are at 24" o/c and they don't have window reinforcing. The concrete subs engineer is looking into it now.

While this is not an option I'm willing to take, you might want to look at section 14.2.7:

14.2.7 — Quantity of reinforcement and limits of thickness required by 14.3 and 14.5 shall be permitted to be waived where structural analysis shows adequate strength and stability. (where14.3 is the minimum steel section with the bars at 18" o/c max.)

I have also found the IRC interesting - When ACI 318 ...[is] used to design concrete ... foundation walls, project drawings, typical details and specifications are not required to bear the seal of the architect or engineer responsible for design...   I never point this particular clause out to clients.

Jordan

Jeff Hedman wrote:

 My numbers show the walls could work with #4 bars @ 24” o.c. each way other than it doesn’t meet the maximum spacing requirements.  Looking at IRC Table R611.3(2) it says for an 8’-0” tall 5.5” core ICF wall with 30 psf wind pressure I can use #4 bars @ 48” o.c. each way.   Now don’t get me wrong I would NEVER be willing to stamp anything with bars spaced that far apart.