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RE: horizontal bar distance below top of wall?

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Scott:

If tolerance relative to what is indicated on the drawings is the issue,
then the code does not really do much in this area.  Most real tolerance
issues will be outlined in the contract documents, which you would be
better able to say whether or not a code offical has direct authority to
require such adherance (sp?) if the engineer of record is not pushing it.

In the IBC code there is section 1907.5.2.  More specificically section
1907.5.2.1.  It would be somewhat debatable if this provision would really
apply to your specific situation or not.  These same basic provisions are
now also in the ACI 318-02 in section 7.5.  Basically it gives tolerances
on the d distance for tension reinforcement in flexural members (which
would potentially effect the lateral position tolerance for a wall but
not likely the vertical position tolerance) and minimum cover in all
members.  Thus, it would seem that is the top layer of reinforcement is
spaced below the top of the wall much greater than minimum cover, these
tolerances would not likely apply.

You other place to look would be the contract specifications/documents.
If the engineer of record was on top of things, then there should be some
tolerance requirements for concrete "things" in the specs.  Many times
this will basically be in the form of referencing ACI 117.  If so, then
there will likely be a tolerance requirement that outlines how far from
what is indicated on the plans the contractor can deviate.  Now, I
honestly don't know if such things would be in the realm of code official
enforcement (to some degree, I would think so since the specifications
have just as much authority as the drawings and in fact are meant to be
"part" of the drawings...thus, if there are tolerances in the specs and
the drawings clearly show a "required" location for some thing and the
contractor does not place that "thing" within the required location +/-
the tolerance, then in effect they are not following the drawings).  Thus,
I leave that to others to really determine.

As to the requirement that you point out from the IRC and the plain
concrete portion of the IBC, it means very little to me.  Do those
provisions give a clear definition for what they define as "top" (i.e.
within the top 5 in)?  If it is basically only what you show (i.e. put a
#4 at the top), then this basically says to me that you must put a bar
somewhere near the top of the wall in a wall that otherwise has not
reinforcment.  In otherwords, it is no better than the reinforced case
that your are looking for an answer to...there needs to be a bar up there
but does not specify exactly where.  Obviously, common sense would say it
should be reasonable close to the top of the wall (i.e. 6 inches +/-).
Common sense, however, would say the same thing for the reinforced case
too.  The problems for both situations is that what is common sense to me
many not be common sense to others.

The end result is that the code does not seem to provide much guidance or
requirements in this area, either in terms of tolerance relative to what
is shown on the drawings by the EOR _OR_ in terms of what requirements
might be placed on the EOR in designing/determining the location to show
on the drawings.  In the end, your best bet may end up being what is
required in the project specs.  If they refer to ACI 117, then sections
2.2.4 and/or 2.2.5 would be of interest.

HTH,

Scott
Ypsilanti, MI


On Fri, 5 Sep 2003, Haan, Scott M. wrote:

> Thanks to respondents   My question is what kind of tolerance is acceptable
> on an inspection?  Cover is not the problem.  It has upset contractors and
> engineers when ispectors have pointed out the field condition at the top of
> the wall varies from a plan detail or note.
>
> You would think you would want the bar close to the top but the way the code
> is written you could start the first bar at least a spacing from the top for
> a reinforcement ratio or shear if required.  For residential seismic design
> category D foundation construction IRC R403.1.3.1 requires foundation stem
> walls to have "... a minimum of one number 4 bar at the top of the wall...".
> IBC 1910.4.4.2 has the same requirement for plain concrete foundations. My
> question is more for a reinforced wall application.
>
> -----Original Message-----
> From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
> Sent: Thursday, September 04, 2003 8:14 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: horizontal bar distance below top of wall?
>
>
> Scott:
>
> I am not aware of anything in either the ACI 318 code or the 2000 IBC that
> would give a maximum permitted distance for the first layer of rebar from
> the top of a wall.  The only thing that would "come close" would be cover
> requirements (but that gives what the minimum distance would be rather
> than what the maximum distance would be) or what would be required to
> satisfy shear provisions (i.e. section 11.5.4.1 of ACI 318 which states
> "spacing of shear reinforcement placed perpendicular to axis of member
> shall not exceed d/2 in nonprestressed members or .75h in prestressed
> members, nor 24 in....thus, if shear is really an issue, it would seem
> that a maximum limit for the top layer of the wall steel [assuming it is
> needed to resist shear] would be at d/2 [which would likely be a large
> number] or 24 in.).
>
> Now, presumably as well, it would still be the engineer's "responsibility"
> to ensure that the bar locations could still achieve the minimum required
> ratio.  So, to some degree, there could be an arguement made that if
> spacing the first layer of bars at the full spacing causes the overall
> ratio to be slightly below the minimum code required ratio, then the
> engineer would need to adjust the spacing of that first layer to meet the
> ratio requirements.  OTOH, the response to the arguement is that if you
> are missing the ratio by such a small amount (i.e. a couple percent off),
> that you are still meeting the intent of the code.
>
> The only other thing that give some "ammunition" would be section 1910.4.3
> of the 2000 IBC that gives tie requirements for the top of columns with
> anchors in them for Seismic Design Catergory C or above.  One could
> logically extend such a need for walls that might have anchor bolts in
> them (although, truth be told, the code does not require that).  One could
> further extend the logic beyond that, but again it would be required by
> the code.
>
> As to my own practice, I generally have the first layer of wall
> reinforcement at about the cover distance from the top of the wall.  This
> is assuming that the wall stops at that level (i.e. like a basement wall
> or retaining wall).  A wall that continues is a WHOLE other matter.
>
> HTH,
>
> Scott
> Ypsilanti, MI
>
>
> On Thu, 4 Sep 2003, Haan, Scott M. wrote:
>
> > Hello:
> >
> > How far can the first horizontal bar be below the top of a poured concrete
> > wall?  Code reference?  It seems you would need one in the first half of a
> > spacing to get your reinforcement ratio or if it was required for shear.
> Is
> > there something that says you need to have reinforcement within a certain
> > definite distance?  Thanks.
> >
> > Respectfully,
> >
> > Scott M. Haan P.E.
> > Chief of Building Inspections
> > Municipality of Anchorage
> > Development Services  Department
> > phone: 343-8330
> > fax: 343-8200
> > cell: 317-6934
> >
> >
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