reinforcement in foundations 1

[allisch]

I'm taking a poll.
And this is not about the cost of rebar versus foundation problems.

Code allows unreinforced concrete footings, and for that matter, even unreinforced basement walls to a certain height.

So how would you deal with questions on rebar tying if in that instance the code does not even require any reinforcement?

Eg. would you allow then to "wet-stab" reinforcement bars, in the instance where none is actually required by code? Yet, ACI and ICC requires reinforcement to be secured in place before concrete is placed?

The contractor is trying to argue that since none is actually required (they could meet the requirements of the unreinforced foundation tables given in the ICC), that they do not have to tie it in place prior to placing the concrete.
It could theoretically all fall to the bottom and they would still meet the code for the unreinforced footings.

It is my position that if it is present, then it must be tied per ACI. The next question is this... If it is present, does it need to comply with the rho min etc.

What do you require for a 8" concrete basement wall as far as reinforcing?
(Sandy Soils=SW - 8' wall ht, 8' minus4" slab minus 8" top of wall to grade = 7' unbalanced fill.)

I'm pretty sure that I know the answer to this, but before you answer, check out 2000 IBC Table 1805.5(1). or other table number if in a state with newer codes.

 

[DRC1]

The reality is that much of these situations are wet stabbed, esp. dowels. If it is not required, then why is it being added? if it if for stength, then I would say it should be tied per ACI. If it is just to provide a connection, then I would be okay with wet stabbing.

 

[MiketheEngineer]

Even the IRC 2006 has prescriptive methods that don't meet ACI - I guess to save money. Just how much does a few pieces of rebar cost to install - esp on a $1,000,000 house!!!

Many years ago on an average 30' x 60' one story house - I figured that if #4 rebar was put on 24'' centers vertically and horizontally (maybe it was 16'') you could probably remove half the soil and the foundation would not fail - house might tumble into the hole (however).

Doesn't make sense to me.

Also - most foundation cracks would never occur.

 

[msquared48]

Remember that you are the Structural engineer of record and it is YOUR liability, not the contractor's you are talking about here. Also remember that the code requirements are a design MINIMUM for the engineer to follow.

Consequently, I do what makes ME comfortable in the seismic zone and soil conditions I see for the various projects I design. Rebar is cheap in comparison to foundation repairs and lawsuits. Don't let the contractor call the shots here.

Tell him to show you his structural engineering license, or keep his )(*&^^%%$^ mouth shut, putting it bluntly.

Mike McCann
MMC Engineering

 

[allisch]

OK-I understand what Mike is saying, but to re-iterate---this is not a question of the cost of rebar versus foundation problems.

Let's get back to the original question-
I will re-phrase it so people understand the question better.

The question is if the presence of reinforcement drives the requirement for the reinforced provisions of ACI, even though no steel is actually required by ACI 318-05.

Read ACI 318-05 22.4.6

Thanks

 

[csd72]

My understanding is that if it meets the requirements for plain concrete then the minimum reinforcement rules do not apply.

I would stress that rusting reinforcement potentially creates spalling regardless of the code provisions followed. So if you have rebar in there make sure it has adequate cover.

 

[MiketheEngineer]

Ditto to Mike McCann

 

[swearingen]

I do have a problem with not tying the reinforcement. If all of the bars fell to the bottom of the hole, you would have very little concrete there and very little resistance to shear. Similarly, if the reinforcement bunches up to a form on one side, it is taking the place of the concrete, not bonding properly, and would actually reduce the strength of the wall.

My opinion is that if reinforcement is there, whether required or not, it must be placed and tied to code.



If you "heard" it on the internet, it's guilty until proven innocent. - DCS

 

[allisch]

swearingen-

Ahhh --you are thinking of a concrete basement wall- I see.
Yes I see and agree with that point 100%.

My fault- I threw you off with my initial post.

The basement wall comment was just to get people to see that the steel that we would normally design for a basement wall is apparently WAY off from what the unreinforced provisions will actually allow. (Not that I would ever consider an unreinforced basement wall). I just added that so that people who didn't even know that unreinforced provisions exist could scratch their heads.
Apparently there is magic concrete that makes up for the loss of steel in basement walls. (and that is another whole topic.)

Thanks for the feedback.
Excellent food for thought-nice logic- good argument stopper!

 

[IFRs]

I'd say that if rebar is not required but being used then some method should be used to insure it's placement so proper cover is assured and the rebar does not bunch up. If the contractor has a plan that you approve (and verify by inspection) fine. If the contractor does not have a plan then show them ACI. There is nothing inherently wrong with "stabbing" unless it is done in a sloppy manner...

 

[civilperson]

Any amount of reinforcement less than the minimum placed in concrete makes the design of the concrete per Chapter 22 - Structural Plain Concrete, (no strength shall be assigned to steel reinforcement that may be present.) Clear cover limitations still apply to reinforcement. No requirements exist in ACI code for secure reinforcement in Stuctural Plain Concrete.