RE: Pre-engineered Metal Building[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: RE: Pre-engineered Metal Building
- From: Charles Espenlaub <Cespenlaub(--nospam--at)martinaia.com>
- Date: Wed, 28 Feb 2001 13:17:48 -0500
Doesn't the hairpin lap with the WWF in the slab, which then can act as the tension tie reinforcing between opposing columns. I thought that that was why the hairpins always had a wide spread on them, to engage enough WWF (to give you enough As) for the tension. With this assumption, it is possible to assume no slab to subgrade friction.
Of course, the above assumes that the WWF is placed properly in the slab.
On the other hand, a slab on a vapor barrier does not have a coefficient of friction of zero. I would, however, agree that the coefficient is lower than if no vapor barrier is used. I seem to recall that the PTI design manual for slab on grade design gave some rule of thumb values for the friction coefficient for a slab with a vapor barrier. Unfortunately, I no longer have a copy of it, so I can not pass along the value(s).
Charles F. Espenlaub, III, P.E.
From: John Riley [mailto:jpriley485(--nospam--at)peoplepc.com]
Sent: Wednesday, February 28, 2001 11:52 AM
Subject: Re: Pre-engineered Metal Building
I have a problem with using hairpins, PERIOD.
The hairpin solution to horizontal thrust requires resistance to be developed through friction between the slab and subgrade. If the slab is cast directly onto the subgrade, I would assume no more than about 0.30 for the coefficient of friction, and that's prior to applying a factor of safety (suggest 1.5 minimum). And if a vapor barrier is used under the slab, I suggest the coefficient is zero. Furthermore, you must determine the size of slab mobilized and reinforce accordingly.
A better solution, in my opinion, is to tie opposing piers together with deformed bars.
By the way, hairpins are used around these parts, without problems as far as I know. And if I could get them to work on paper, I'd specify them because they are cheaper. Probably the reason they work in real life is that passive resistance is achieved in the backfill soil. But passive resistance offered by soil within frost depth (42" here) should be ignored.
Just an opinion.
John P. Riley, PE, SE
20 Oakwood Drive, Blue Grass, Iowa 52726
Tel & Fax: 319-381-3949
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