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RE: shear friction from horizontal top reinforcement, to resist holdown anchor pop out in A footing?[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: shear friction from horizontal top reinforcement, to resist holdown anchor pop out in A footing?
- From: "Roy Harrison" <tectonic(--nospam--at)bigpond.net.au>
- Date: Thu, 5 Oct 2006 09:37:06 +0930
I would also be interested in seeing your solution, if you would email it to me. We tend to use the pullout cone method, but we generally use mass concrete bored piers (unreinf. circular pile) here.
The notions you propose make sense. I believe there are at least two mechanisms of failure
1) is debonding of the rod, of which we here very little these days and
2) shear cone failure of the concrete.
To overcome debonding sufficient anchorage length is required. Where this is not available in a straight length we would put a 90deg bend on the end of the bar. However for large diameter bars developing large tension forces a local compression failure can occur at the concrete interface on the inside of the bend. This is a function of the bend radius and I have an old copy of a C&CA (UK) handbooks that has a design approach for this problem, where the radius of the bend is modified from the standard radius to minimise the compression. An alternative was to go with the standard bend but put a large dia. pin bar inside the radius to distribute the bearing and provide a dowel action.
With regard to the shear cone failure, the SAA concrete code has an approach for flat slabs where a steel shear head is cast into the slab. (I think this was also in the ACI, I've not seen one for some years). To me the basic notion of the shear head is to actually increase the shear perimeter, ie enlarge the pull-out cone surface area, for shear.
But as suggested earlier in the list "there is not a conspicuous history of failures" from this mechanism, to paraphrase a local document.
Roy Harrison & Associates
Structural Design Engineers
Para Hills - South Australia
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