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Re: Hairpins in footings

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For Metal buildings: This information is provided in Metal Building Systems
book by MBMA. There is a section on hairpins. Diagram is also provided for
clarity.

The horizontal thrust from the rigid frame column is distributed by hair-pin.
This thrust is then transferred by adequate bond length of hairpin and then to
the slab reinforcement and then into the ground.

Analysis utilizes floor slab reinforcement of the building which acts as the
final tensile element.

For 4" slab with 6x6 - 10/10 mesh at mid-depth, As = 0.029 in^2.
Hairpin angle = 30 degrees from gridline of  rigid frame.
Ft = 0.029(Fy)x(2.732xLt)
Ft = Horizontal thrust
Fy = is for mesh , say 20000 PSI
Lt = length of hair-pin - each side of gridline for frame into the slab
Ft = 1584xLt

Thus, for H =12K
Lt = 7.57 ft.
Thus, the length of the hairpin is to be say 8' for each side.

e.g. For slab with #4 at 12" O.C. both ways(assuming at mid-depth)
Ft = 10924xLt

The thing to watch out is the transfer of horizontal thrust from column to
base plate, anchor bolts, thrust angles and then the location of hair-pin(edge
and mid-depth of slab). Also, one will have to be careful about the edge of
slab in relation to anchor bolts and hair-pin location.


Shirish V. Mistry, S.E.


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