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Re: Pre-engineered Metal Building

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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
Riley Engineering
20 Oakwood Drive, Blue Grass, Iowa 52726
Tel & Fax:  319-381-3949
----- Original Message -----
Sent: Wednesday, February 28, 2001 8:36 AM
Subject: Pre-engineered Metal Building

I have a situation where the bearing elevation for the columns of a metal building is below the finished floor elevation by 4".  The slab is 6" thick.  The detail I usually use has the hairpin anchored to the anchor bolts though a mechanical connection.  This is not possible in this situation.  Has anyone seen a detail where the hairpin runs through a hole drilled in the column web?  Does anyone see any problems with this?  Any help would be appreciated.
Thank you,
Chris Towne, E.I.T. (Pending Test Results)
Chapman Technical Group