3000 psi Concrete Requirement
3000 psi Concrete Requirement
(OP)
I have a small residential metal building foundation (30 X 42) on uneven topo with some exterior foundation walls having up to four feet of concrete exposed to the weather. The owner received a comment back from the local jurisdiction (King County) that 3000 psi concrete is required in this area of exposed concrete. This will throw the concrete into the inspected range since it is over 2500 psi. The requirement seems ridiculous to me.
Does anyone know of a specific code reference in the IBC requiring this 3000 figure in this circumstance? If not, then I may be dealing with a local upgrade, or an over exuberant plans examiner trying to be an engineer.
Yea... like that never happens.
Does anyone know of a specific code reference in the IBC requiring this 3000 figure in this circumstance? If not, then I may be dealing with a local upgrade, or an over exuberant plans examiner trying to be an engineer.
Yea... like that never happens.
Mike McCann
MMC Engineering






RE: 3000 psi Concrete Requirement
The 3,000 psi requirement could possibly be a local amendment but you'd have to check with that jurisdictions website or call the bldg department to see where that comes from.
Also, according to the IBC, a building official has the right to increase the minimum requirements of the IBC (they can't diminish them).
RE: 3000 psi Concrete Requirement
Mike,
See 2003 IBC Section 1904 and Table 1904.2.2(2). King County WA may be in a moderate or severe exposure region. By this table it would require 3,000 psi concrete because it is a vertical surface exposed to the weather.
Ralph
Structures Consulting
Northeast USA
RE: 3000 psi Concrete Requirement
This is not a code provision, but a general industry standard to protect the supplier from future nuisance claims later. Since there is just such a small cost differential, there is really no problem.
You have a hard time getting concrete here for an external slab unless it is 4000 psi and air entrained unless the person on site signs and it responsible. - Life is too short and precious for "penny-pinching" on materials when labor is the real cost.
Localities have some latitude on codes and acceptance, but not every supplier is willing to accept the consequences.
RE: 3000 psi Concrete Requirement
RE: 3000 psi Concrete Requirement
I see the table referred to here and it looks like 3000 psi is required as it is in a 40 psf snow load area. Moreover, and more importantly, the owner is refrigerating the slab with cooling coils and insulating under the slab of which I was not aware.
I also see that he is installing 40 psi foam under the spread footings too. I don't like it, but if the 40 psi figure is the compressive strength of the foam, I guess it is OK.
Thanks guys.
Mike McCann
MMC Engineering
RE: 3000 psi Concrete Requirement
In your area, Minnesota, I can completely understand that. However, our winter weather is much milder here and 2500 psi is regularly specifleied and available, or at least it has been in the past.
From the looks of the IBC table referred to above though, it looks like I will have to change my thinking and specifying on the subject, at least pertaining to commercial. I am going to check the IRC to see if the same table applies.
Mike McCann
MMC Engineering
RE: 3000 psi Concrete Requirement
The code is only the least restrictive standard that you can use and be legal, but it is not always correct or proper.
In our area, there is little external control (especially with extremely price conscious contractors) that the industry has some concrete major producers have set a higher standard because the ultimate use of the material is not known. Some suppliers will not unload without a signed waiver if it is apparent it is for exposed purposes. - It eliminates nuisance claims and suits where the timing and placement could really be the culprits. There will always be the low priced producers because they think they have some cost saving secrets.
The difference in the per yard material cost is minimal and not significant when compared to the labor and potential liability for the supplier and contractor. The price people just go to the small low bidders and try to get performance. At times, I feel like we are in a jungle surrounded out of area bidders that is sitting on good aggregate deposits.
I am not in the ready-mix business, but have been involved for over 40 years (starting as summer concrete inspector on state projects)and marveled at the differences across the country and in other countries. - Now Al Franken will have to be "Minnesota Nice" if that is possible after his 25 year hiatus.
RE: 3000 psi Concrete Requirement
RE: 3000 psi Concrete Requirement
I think that with the old 97 UBC that we use to spec. 2500 psi concrete to not require Special Inspection on residential projects.
Now, Section 1704.4 Exceptions allows Light Framed Construction with out Special Inspection. But, I don't see anything in the 2006 IBC that required 3000 psi concrete.
Maybe the Building Official is just adding his own specs to the code. You might ask him where he has found something, in the code, that required 3000 psi concrete.
I suspect, that when push comes to shove, that the concrete probably has a minimum compressive strength greater than 3000 psi.
RE: 3000 psi Concrete Requirement
RE: 3000 psi Concrete Requirement
According to the IBC section and table RHTPE quoted in his post above, it is required for the project as it is in the Ravensdale area of Washington. As I previously said, I am going to change my specs and thinking here.
Mike McCann
MMC Engineering
RE: 3000 psi Concrete Requirement
RE: 3000 psi Concrete Requirement
RE: 3000 psi Concrete Requirement
Mike McCann
MMC Engineering
RE: 3000 psi Concrete Requirement
BigH, a mud mat/blinding is not structural concrete. 10 MPa is fine. 3000 psi is 20.7 MPa.
RE: 3000 psi Concrete Requirement
RE: 3000 psi Concrete Requirement
RE: 3000 psi Concrete Requirement
RE: 3000 psi Concrete Requirement
So what if it needs inspection? It is a good thing for a designer to have a second set of eyes keeping him safe.
It reminds me of when I started out and it got busy in the office and the boss hired a moonlighting professor to help out. We got the markup plan back for a small building addition with 4" deep roof beams! The professor's reply to the boss's remark that we never use and probably can't get those was "that's all that the calculations called for."
That phrase has never left me, showing how designers can be just as unrealistic as contractors.
RE: 3000 psi Concrete Requirement
RE: 3000 psi Concrete Requirement
Sandman21 may be correct - See 1704.4, paragraph 2.3, which is part of a list of exceptions.
BUT, as I read that section more carefully, I suspect the exceptions apply only to footings.
Ralph
Structures Consulting
Northeast USA
RE: 3000 psi Concrete Requirement
RE: 3000 psi Concrete Requirement
The section I mentioned in my pervious post is a DSA requirement which does not apply.
RE: 3000 psi Concrete Requirement
Also, according to the IBC, a building official has the right to increase the minimum requirements of the IBC (they can't diminish them).
Can the building official do this, or is it a matter of a local building by-law? Seems like they are being given more clout than they deserve...
Dik
RE: 3000 psi Concrete Requirement
He believes they are way overstepping their bounds but what do you do about it when they have the power to grant building permits?
I thought Chapter 1 of the IBC gave direct power to the building official to increase the minimum standards of the code but I couldn't find it directly.
My son and his firm are thinking about complaining to a higher authority in their city (not prayers) but that has its pitfalls too.
RE: 3000 psi Concrete Requirement