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RE: bar spacing in a wall

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It seems to me that maximum bar spacing should be a function of member thickness and span - similar to effective flange width for T-beams in Section 8.12/ACI 318-08.  Rationally there must be some "zone of influence" of a single bar in concrete beyond which protection against cracking is significantly reduced.

Bill Sherman
CH2M HILL / DEN
720-286-2792
 

> -----Original Message-----
> From: Gil Brock [mailto:gil(--nospam--at)raptsoftware.com] 
> Sent: Friday, September 04, 2009 2:54 PM
> To: seaint(--nospam--at)seaint.org
> Subject: re: bar spacing in a wall
> 
> Andrew,
> 
> You cannot achieve reasonable crack control with bar spacings 
> greater than 18" according to ACI. Other codes have since 
> reduced this to 12" 
> (Eurocode and AS3600). Wider than that and the crack width 
> between the bars is not controlled by the bar. BS8110 
> theoretically allows 750mm (30") as an absolute maximum but 
> not if you want good crack control for which they give 
> reduced values depending on certain factors I cannot remember 
> (code is at work). So, yes, it has to do with the Z factor 
> and its replacement method.
> 
> It has nothing to do with warm and fuzzies and little to do 
> with strength, except that for a cantilever wall for strength 
> I would not think you would want a spacing greater than the 
> wall height, but probably significantly less than that, say 
> about half wall height.
> 
> 
> At 01:43 AM 5/09/2009, you wrote:
> >I should not post twice on the same subject, but I will be that guy 
> >because it is Friday and I am feeling chippy, hombre.
> >
> >Riddle me this batman, why in one situation could I go with 
> 8" CMU with 
> >#4@48" o.c. in solid grouted cells but ACI would require me 
> to go 18" 
> >o.c. max for that same wall if it is 6" solid poured? I have 
> done more 
> >than my fair share of CMU calcs so I understand the 
> intricacies, I want 
> >a common sense type answer. Don't blind me with your 
> science. I think 
> >the answer is somewhere between a longstanding ACI minimum 
> that gives 
> >people warm and fuzzies, and something to do with bond stress or the 
> >old Z factor or something? I don't have my ACI around and I 
> don't have 
> >it memorized like Scott, but I bet he knows the answer.
> >
> >But Jeff says the IRC table says 48" o.c. for 30 psf, which 
> makes sense 
> >from a CMU perspective, and we all know about CMU being of much less 
> >compressive strength than solid concrete. I have also heard 
> people in 
> >the ICF business throw 48" o.c. out there also.
> >There has to be some science or testing behind this, but it from a 
> >residential wall standpoint it would seem about right. (I 
> still would 
> >pay the extra for my house from a crack control perspective).
> >
> >I digress. Rebar, we talkin about rebar? REBAR? REBAR? 
> (Allen Iverson 
> >talkin about practice). How much more, anyone anyone anyone, 
> can this 
> >860sf addition cost either way for say about 20-30 more 
> bars? Have the 
> >GC tell you, then bill him for your extra time on this list 
> and doing 
> >research and call it even. Add in our time as "consulting and 
> >research".
> >
> >Its 100am where Conrad in Adelaide is, means we can all have 
> a beer now right?
> >
> >
> >Andrew Kester, PE
> >Orlando, FL
> >
> >
> 
> Regards  Gil Brock
> Prestressed Concrete Design Consultants Pty. Ltd. (ABN 84 003 163 586)
> 5 Cameron Street Beenleigh Qld 4207 Australia
> Ph +61 7 3807 8022              Fax +61 7 3807 8422
> email:          gil(--nospam--at)raptsoftware.com
> email:          sales(--nospam--at)raptsoftware.com
> email:          support(--nospam--at)raptsoftware.com
> webpage:        http://www.raptsoftware.com
> 
> 
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