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ACI 117 Tolerances

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bookowski

Structural
Aug 29, 2010
983
My understanding is that ACI 117 allows for +/- 1" at slab edges in/out tolerance in plan (horizontal deviation). Is that correct? Is there any limit for floor to floor alignment/variation? The +/- 1" means that you could have +1" at one floor, -1" at the next. So building facade connections need to account for up to 2" variation in/out between floors if the tolerances are only limited to 117? It also allows +/-3/4" up/down in elevation - so this adds another 1-1/2" up down and that doesn't account for deflections. If the above is correct it seems that more stringent tolerances should be specified, or at least additional floor to floor variation limitations. Are 117 tolerances standard spec?
 
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1" is the max. offset for the intended vertical position.

This creates a plus and minus boundary on either side of a line of column going upward through the floors.

So you can't allow an accumulation of offsets (i.e. the second floor can't be 2" out of position - it also has to be within 1" of its original intended position).


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I agree that a 2nd floor can't be 2" out of its theoretical position, but it can be 2" out from the floor below correct? If the floor 5 is +1" and floor 6 is -1" then you have a 2" plan dimension offset between the two. The facade will have to accommodate the most "+" extent and will be plumb so you'd have a 2" gap to accommodate in your facade connection. Similar for up/down, with 3/4" per floor you could have 1.5" between two adjacent floors. Seems like a lot to ask of the facade connections.
 
Yes - 1" at one floor going one way and 1" at the next floor going the other way is still within the 1" +/- requirement and a total of 2" from one floor to the other. At least that is the way I see it from 117 verbiage.


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I agree on the total of 2". You need to get the tolerances for the facade system itself, and set your concrete and connection tolerances accordingly.
 
I guess my question is whether this ACI spec is common and what is the penalty for specifying tighter tolerances. The 2" in/out, 1.5" up/down seems like a lot to build into facades - just wondering if people are tightening that up.
 
All the finish systems seem to call for tighter tolerances than the concrete or steel standards. If that is what is being specified tighten up your tolerances and let the architect/owner know that may be increased costs.
 
bookowski - that diagram I posted came from this URL - it appears to be a seminar of some type where the speaker gives a history of ACI's attempt over the years to establish 117 and the tolerances we have today. His main point is that many tolerances are not based on any true studies, research, or realities and have resulted in some very unattainable limits. That said, it would seem to my gut that the 1" column limit is doable. If you tighten up the spec it may be you are approaching what this guy's seminar ridicules...i.e. you can specify it but you won't get it.

Don't get me wrong - I haven't thought much on it to form a full opinion - just relaying what his point was.

Tolerance Traps link:



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The 1" is the maximum value, subject to the 0.2% or 0.3% limit, and only for relatively short buildings. Taller structures have different limits. See below for text of the first part of ACI 117 section 4.1

ACI 117 reports the tolerances generated by other ACI committees (318, 301, 315, etc.), and may generate new tolerances where one is needed but hasn't been established. At the last ACI convention, I asked Committee 117 to determine and track "ownership" of tolerances. They are currently working on this and in short order should be able to verify where all tolerances in the document originated. Going forward, this will help with validation of tolerances and should avoid unresolved conflicts where multiple committees or standards have disparate values.

Where ACI 318 and 301 are in use, ACI 117 is the controlling tolerance document UNLESS other tolerances are specified in the contract documents. I hesitate to make different tolerances since the industry prices work based on the "state of the practice". When doing so, I recommend making the deviation clear so it can be priced and constructed according to your plans.

ACI 117.1R-14 Guide for Tolerance Compatibility in Concrete Construction provides information about what to do to prevent problems when one tolerance conflicts with another... for instance, concrete placement tolerances and in-service deflections that could interfere with wall systems.

From ACI 117-10:
4.1.1 For heights less than or equal to 83 ft 4 in.
For lines, surfaces, corners, and arrises: the lesser of
0.3% times the height above the top of foundations or
lowest support level as shown on Project Drawings
or ±1 in. This section shall not be used to evaluate local
departure from a specified plane or form irregularities.
Refer to Section 4.8.2 and 4.8.3, respectively.
For the outside corner of an exposed corner column
and grooves in exposed concrete: the lesser of 0.2%
times the height above the top of foundations or lowest
support level as shown on Project Drawings or ±1/2 in.
This section shall not be used to evaluate local departure
from a specified plane or form irregularities. Refer
to Section 4.8.2 and 4.8.3, respectively.
...
 
4.1 is deviation from plumb, not horizontal deviation. Sounds like the +/-1" for slab edge is fairly standard - was just checking that this was standard practice, 2" total sounded like a lot to accommodate.
 
In case anyone else has the same question: I asked around and in my area +/- 1/2" up/down/in/out for slabs is standard with no penalty, that is sometimes halved for crucial areas.
 
In my limited experience with ACI and PCI tolerances, I have found them to be quite generous. This might be due to the fact that ACI and PCI are funded, to a large extext, by contractors and suppliers.
 
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