Dumb question time - vertical rebar and foundation starter bars
Last Post 15 Feb 2012 08:08 PM by Alton. 10 Replies.
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aa_ukUser is Offline
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14 Feb 2012 04:31 PM
Does the vertical rebar in an ICF wall have to match up with the starter bars sticking out of the foundations?

It's pretty obvious why rebar has to be overlapped in a wall but does the vertical rebar have to match up with the starter bars in the foundations?

I thought that the starter bars were there to stop any lateral movement of the building rather than to add strength to the walls.   Or am I wrong?

Thanks

Andrew
AltonUser is Offline
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14 Feb 2012 04:41 PM
The practice that I have always seen is that the vertical rebars are actually attached to the dowels in the footer.  I know that with a tall backfilled wall, I would prefer to see the vertical rebar tied to the rebar dowels.  What does the building code say in your area?
Residential Designer & Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu, 334 826-3979
aa_ukUser is Offline
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14 Feb 2012 05:00 PM
I'm in the UK where ICF isn't used as much.  As a result the building code doesn't explicitly cover it.

I have been looking through as many of the ICF manuals as I can find and some say do it and some say do it where you need to.  There is a Logix technical bulletin that explicitly says that you don't need to match them up for residential.  It says:

"Footing dowels connects the wall to the footing (see Figure 4). This prevents wall movement at the wall/footing joint caused mainly by soil loads. In residential construction, the vertical rebar in the wall itself does not contribute to the strength of the wall/footing connection and hence is not required to splice with the footing or match the spacing of the footing dowels. In cases, where lap splice may be required, non-contact lap splices are permitted."

In order to use a product in the UK it does need to have what is called a BBA Certificate.  I'm using Nudura and the certificate for it shows a non-contact lap splice with the starter bars so that's what I'll go for.
AltonUser is Offline
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14 Feb 2012 06:57 PM
Since you do not plan to connect the footer dowels to the vertical rebars, then have you considered using a keyway in the footer.  Not required but does help lock the wall to the footer.  I guess a keyway could be used ok with Nudura blocks.  If the walls are above grade, then a keyway would not serve much purpose.
Residential Designer & Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu, 334 826-3979
Chris JohnsonUser is Offline
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14 Feb 2012 08:35 PM
Your footing dowels are to hold the bottom of the wall

Vertical bar provides the strength in the wall

Matching is not required

In a typical cast in place walls, regular forms, the verticals are tied to the dowels to prevent the cage from shifting out of location, in ICF since we stagger our horizontal bars which holds the vertical bars when placed from the top the cage does not shift.

Unfortunately history shows the typical cast walls which involves a lot of steel tying and those in charge of inspecting/designing are not always familiar with the advantages of ICF and cannot get past the ease of which we do things compared to yesteryear I'm not saying it's wrong, I am saying it is unnecessary

Chris Johnson - Pro ICF
North of 49
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15 Feb 2012 03:25 AM
Thanks for the replies. Much appreciated.
Jerry D. Coombs, PEUser is Offline
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15 Feb 2012 02:26 PM
No, but it's supposed to be within 6" to be considered "associated" with it. It's a good idea to be within that.
No keyway is needed as long as you leave the surface rough; as a matter of fact it's often better without it. But the dowel MUST be long enough to develop for the shear friction.
Jerry D. Coombs, P.E.
Coombs Engineering, P.C.

You can have with quality; You can have it fast; You can have it cheap. Pick any two.
AltonUser is Offline
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15 Feb 2012 05:52 PM
Mr. Coombs,

Just curious, but why it is better without a keyway?
Residential Designer & Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu, 334 826-3979
TexasICFUser is Offline
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15 Feb 2012 06:20 PM
I don't know about the keyway and will wait for Jerry's response but in the meantime.... the logic behind Jerry's six inches between bars (if you care) is ACI-318 non-contact splice - bar must be within 1/5 lap length of other bar. E.g. -- for 40 diameter min lap this is 25 inches for #5 or 5 inches. Jerry's probably a 48 diameter min guy and thus 6 inches is the target min and not five. Regards.
Jerry D. Coombs, PEUser is Offline
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15 Feb 2012 07:31 PM
Tex-
Close enough- very perceptive. The code is 1/5 Ld or 6", whichever is less. I typically tend toward long splices, so I default to 6"
But in this case, the Ld is short (and usually will be) so the 6" is wrong. It will probably be more like 3-5" (but I won't go through the calcs- see below). Thanks for catching me on that. However, if it's a lightly loaded wall (above ground), I've successfully argued for a short (16") dowel AND a 6" offset. It's all slight-of-hand...

Alton-
Not easy to go through without drawings, but here goes:
If you design the base shear of a wall with a heavy lateral load using shear friction (ACI 318 11.6) you get the advantage of the full width of the wall IF the bar is developed well (see above).
If you introduce a keyway, you no longer get that benefit, and you default to the old mechanical-connection shear; the keyway. The useable depth of the wall that can be used for shear calculation is from the loaded face of the wall to the far face of the keyway. Depending on how/ where it's installed, that will be between 1/2 to 2/3 of the thickness of the wall. A lot of work for a reduction of benefit. If it's not heavily loaded, you don't need a keyway, or even very much dowel.
THERE! Wasn't that fun?!
Jerry D. Coombs, P.E.
Coombs Engineering, P.C.

You can have with quality; You can have it fast; You can have it cheap. Pick any two.
AltonUser is Offline
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15 Feb 2012 08:08 PM
Yes, that makes sense to me.  I guess it is overkill to use both dowels and keyways for the same wall but I have designed that way.  Now, it appears that dowels are the way to go.
Residential Designer & Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu, 334 826-3979
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