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Re: DESIGN / ANALYSIS TREATMENT OF "HAIRPIN CONNECTIONS"

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Occasionly we get involved in foundations for metal buildings. I use hairpin connections at the piers to transfer the column thrust into the floor slab reinforcing if the thrust is of a low magnitude. For higher magnitude thrusts,  I recommend tying between opposite columns with rods, rebar or angle cast in the floor slab.

For the hairpin method, I use the friction between the slab and the subgrade to transfer the forces out of the slab into the ground. There are a number of things to be aware
of with this method:
    1. do not use an unreinforced slab...use WWF or rebar in the slab
    2. make sure sawcuts do not cut the reinforcing at the joints if you are counting on a
    force  transfer to an adjacent slab
    3. a  vapor barrier will reduce the coefficient of friction and will make this
    method impractical
    4. do not count on friction in the failure zone of the backfill (similar to locating
    an anchor wall outside the failure zone for sheet piling)
    5. Extend the haipin far enough to engage as much rebar as necessary to
    safely transfer the forces.

Jim Kestner, P.E.
Green Bay, Wi
 

Robert Rogers wrote:

 I HAVE SEEN (ON SEVERAL DRAWINGS) THE USE OF BENT REINFORCING STEEL
 (USUALLY BENT AT 135 DEGREES) WHICH IS PLACED IN THE TOP OF A CONCRETE
 PIER (JUST BELOW THE COLUMN BASE PLATE AND AROUND THE BACKSIDE OF THE
 ANCHOR BOLTS) AND TIES THE PIER TOP INTO THE CONCRETE SLAB ON GRADE.  THIS
 IS A TYPICAL DETAIL FOR PRE-ENGINEERED METAL BUILDING WHERE THE LATERAL
 THRUST LOAD IS TRANSMITTED INTO THE SLAB-ON-GRADE SUCH THAT IT HELPS
 RESIST ANY LATERAL FORCES.  IF ANYONE KNOWS OF A GOOD DESIGN/ANALYSIS
 REFERENCE FOR THIS CONNECTION PLEASE LET ME KNOW.  (I'M ASSUMING ITS JUST
 A MATTER OF DEVELOPING SUFFICIENT TENSILE STRENGTH IN THE REBAR TO
 TRANSMIT THE THRUST LOAD).
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