Acceptable construction tolerance for rebar placement
Acceptable construction tolerance for rebar placement
(OP)
I am a PE and do concrete design frequently. I also frequently am involved in watching the designed concrete members get built in the field and I am constantly stressed and depressed and aghast at the inattention to detail that the concrete contractors seem to have. It seems they never pay any attention to required edge distances, bottom clearances, embed locations, etc. If they pour a footing with some pedestal rebar coming up out of it, it is always off location by a couple inches. Then when they go to place the forms, the forms will sit right against the rebar and they might push the tops of the bar away from the forms, but the bottoms of the bar will still be pushed up against the forms.
I don't make a fuss if the bar in a wall or mat should be on 12" centers and they end up at 11" on one and 13" on the next. I only make a fuss when the depth to the rebar in a bending member is off by more than 1" or so. And that is because I know that if I change "d" in the calcs by an inch, it can be a substantial change in strength. And I make a fuss about edge distances to forms and the the ground. For some reason 3" clear means "just not sitting right on the ground" to a contractor, and even that is a generous definition to some contractors.
If I say something to the contractor about it they look at me like I am completely nuts, and then they tell me that I am completely nuts if I think they could possibly do it any better than how they are doing it. I am told by contractors on every job that my expectations are completely out of line with what is possible. If I had a nickel for everytime someone has looked me straight in the eye and said, "are you f*ing serious?" I would be rich and could retire.
So my question is, is this standard fare for concrete contractors or do I just happen to have a very bad lot of concrete contractors in my area? Or am I really just expecting the impossible? Does anyone else have experience where the rebar gets placed where it should? What should my expectation be when it comes to rebar placement tolerances?
I don't make a fuss if the bar in a wall or mat should be on 12" centers and they end up at 11" on one and 13" on the next. I only make a fuss when the depth to the rebar in a bending member is off by more than 1" or so. And that is because I know that if I change "d" in the calcs by an inch, it can be a substantial change in strength. And I make a fuss about edge distances to forms and the the ground. For some reason 3" clear means "just not sitting right on the ground" to a contractor, and even that is a generous definition to some contractors.
If I say something to the contractor about it they look at me like I am completely nuts, and then they tell me that I am completely nuts if I think they could possibly do it any better than how they are doing it. I am told by contractors on every job that my expectations are completely out of line with what is possible. If I had a nickel for everytime someone has looked me straight in the eye and said, "are you f*ing serious?" I would be rich and could retire.
So my question is, is this standard fare for concrete contractors or do I just happen to have a very bad lot of concrete contractors in my area? Or am I really just expecting the impossible? Does anyone else have experience where the rebar gets placed where it should? What should my expectation be when it comes to rebar placement tolerances?





RE: Acceptable construction tolerance for rebar placement
Many of the contractors and their staff are plenty intelligent, but have no understanding of what they are building. Better contractors with actual quality control and proper pride do exist, they are just the rare exception.
Keep correcting them, as you must, and nevermind the attitude unless it becomes aggressive or abusive. Brook no opposition to your authority, mind you... If you do they will never correct anything again and simply pour when you're not there, figuring you for a wet noodle who won't do anything about it.
RE: Acceptable construction tolerance for rebar placement
Also CRSI may have some info on that.
Keep in mind there is some degree of latitude in rebar placement - they don't have to be exact and 117 perhaps offers what degree is acceptable.
The phi factors in ACI are partially meant to deal with minor variations in "d".
I would most be concerned with the bar cover.
RE: Acceptable construction tolerance for rebar placement
RE: Acceptable construction tolerance for rebar placement
I'll have to check my books Monday.
RE: Acceptable construction tolerance for rebar placement
I did just find a technical note from CRSI - they reference ACI 117 a bit.
Check out this CRSI Document: Construction Technical Note CTN–M–1–11
Link here. Looks like you can download it free....might have to create a logon registration.
RE: Acceptable construction tolerance for rebar placement
To some degree, CRSI and ACI have a circular reference going. Each refers to the other and neither gives reasonable tolerance limits. See attached CRSI document...this is a free document from CRSI so not a problem posting...
RE: Acceptable construction tolerance for rebar placement
RE: Acceptable construction tolerance for rebar placement
Sort of like:
Architect shows "see structural" on their detail.
Engineer shows "see architectural" on theirs -
both pointing to the same thing.
RE: Acceptable construction tolerance for rebar placement
length splice - +- 25mm
variation in reinforcement
starter bars - one bar dia
slabs and walls - 1/4 indicated spacing
beams and columns - +- 5mm
dimensions of bent bars - +- 5mm
RE: Acceptable construction tolerance for rebar placement
RE: Acceptable construction tolerance for rebar placement
Dik
RE: Acceptable construction tolerance for rebar placement
If you spend a fair amount of time in the field, it may be worth getting a copy of (sales alert) the CRSI Placing Reinforcing Bars book. It explains field practices and is the contractor's reference for bar placement.
RE: Acceptable construction tolerance for rebar placement