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3000 psi Concrete Requirement
2

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.  nosmiley

Mike McCann
MMC Engineering

RE: 3000 psi Concrete Requirement

IBC references ACI 318 and ACI 318 requires a minimum of 2,500 psi.  See ACI section 5.1.1.

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

In our area, you will not even buy or get 2500 psi concrete, unless it is specifically specified in writing. Some lightweight concrete fire protection may be exempted from the requirement, but it may still be over the minimal 3000 psi limit.

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

I agree with concretemasonry - 3,000 psi mix is the minimum I use for any structure, reinforced or non-reinforced. 2,500 is only used for curbs, gutters and sidewalks and this is required by local code.

 

RE: 3000 psi Concrete Requirement

(OP)
I will not argue here, but note that Simpson only requires 2500 psi for most of their holddowns, but provide tables for strengths in excess of that figure too.  

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

(OP)
Concretemasonry:

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

Mike -

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

Just wondering if we are becoming "code" engineers or are we "thinking" engineers?  Do we "follow" the code even if it isn't an absolute necessity from a design point of view?  (I'm thinking about the recent post of hitting bedrock "within" the frost depth required.) 3000 psi (18MPa) is okay by me - but when I do leveling concrete (blinding concrete/mud mat) I wouldn't specify 3000 psi nor even 2500 psi concrete - yet if the code requires . . .   

RE: 3000 psi Concrete Requirement

Mike,
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

the reason a lot of codes require 3,000 psi and a lot of engineers, suppliers and contractors use it for structures is that it has been shown that over the years, it provides a good level of performance. Not just because some code official published it. And by the way, most codes are written and edited by practicing engineers. IF there are special circumstances, this minimum requirement or local preference should be evaluated to see if something stronger might be required.  

RE: 3000 psi Concrete Requirement

(OP)
OldPaperMaker:

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

We've never used any mix under 3000 psi, but we don't do any residential work.  I would spec an air entraining agent for the exposed walls and for the slab, if you expect it to be exposed to freezing temperatures.   

RE: 3000 psi Concrete Requirement

If you show that you only need 2,000, I would assume that you could get the inspection waived, even if you ordered a higher grade. If it were me I would get the 3,000. It will not be much more cost for higher strength and better dependiblility.

RE: 3000 psi Concrete Requirement

(OP)
Interesting thought DRC1, but I do not know that KC will buy it.  I will try though.

Mike McCann
MMC Engineering

RE: 3000 psi Concrete Requirement

What an absolute nonsense your fellows in the US have gotten yourselves into.  3000 psi concrete requires inspection, yet 2500 doesn't.  Go figure.

BigH, a mud mat/blinding is not structural concrete.  10 MPa is fine.  3000 psi is 20.7 MPa.

RE: 3000 psi Concrete Requirement

The higher strength concrete will improve durability.

RE: 3000 psi Concrete Requirement

40 psi is 5.76 ksf, better than most subgrades.

RE: 3000 psi Concrete Requirement

hokie - well aware that mudslab isn't structural - and even 5MPa or less would be sufficient

RE: 3000 psi Concrete Requirement

We never use less than 3000 psi on anything, residences included.

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

I don't have my code but special inspection is still required for 2500 psi concrete, however if you spec. 3500psi and design for 2500 psi, you can waive the batch plant inspection. Section 1704 something.

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

The way around this is you design for 2500 psi (show it on your calcs) but spec out 3000 psi on your plans. Works for me all the time with regards to the plan checker. You won't need a concrete inspection (for 2500 psi or lower per IBC) but you'll get a higher psi concrete. This is the solution if you're just trying to avoid an inspection and satisfy the plan checker.

RE: 3000 psi Concrete Requirement

Section 1704.4.2 exception says it applies to continuous footings under light-frame construction and to concrete foundation walls designed per Table 1805.5(5).  As long as you meet the table and the concrete was designed for 2500 psi special inspection is not required, but spec. the 3000 psi so the plan checker is happy.  

The section I mentioned in my pervious post is a DSA requirement which does not apply.

RE: 3000 psi Concrete Requirement

JAE:
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

My son (an architect) has been recently complaining about their local building officials "practicing architecture" in their plan reviews, requiring all sorts of wild things (one example was in a high school classroom where they required two separate sinks in the chemistry lab vs. the single one they had designed.  The official said something to the effect that they thought it made better sense, allowed for chemicals in one sink and non-chemicals in the other, etc...even though both sink drains immediately went to the same outflow pipe.

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

Your son should be thankful his in not an architect in CA, he would hate DSA, think of the worst building official you have ever had and take it up a 100 notch's. lol  Also lots of people think the BO is stepping over the line when really they are not.

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