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RE: Levelling plates or shims ?

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As many on this list are aware, I am a former iron worker.  I have set many
columns with every method you can imagine.  The shim pack is the most
efficient way to set a column.

In theory using the leveling nuts makes good sense.  In the land of come
alongs, and spud wrenches it does not work that well.

The problems with using leveling nuts are as follows.
1.	Because of tolerance problems, you have to use oversize holes in the
base plate.  With oversize holes, you have to use a plate washer.  The plate
washer will be a minimum of 3/8" thick.  The nut will be about 1" thick
(assuming a 1" diameter anchor bolt).  Vertical alignment per ACI 117
"Standard Specifications for Tolerances for Concrete Construction and
Materials", Sec. 3.3.1.2  is + 1/2" to -2".  This would require an absolute
minimum grout space of 1 5/8".  I have had occasion to use leveling nuts,
but they are rare, and generally are for base plates that are huge and
shipped loose from the column.
2.	They are not as easy to adjust or to plumb the frame as with a
single shim pack in the center.
3.	If the floor is cast first and you are working in a pocket, you
can't get to the bottom nut.
4.	Most iron workers will either not install the bottom nuts at all or
will back them off to the top of the foundation.

The procedure in the single shim pack is:
1.	Shoot the level at the center of the bolt group.  Knowing the level
of the base plate, you set a shim stack that is the height of the difference
in elevations.
2.	Set the column on the shim stack, install the plate washers and the
nuts, and release the choker for the crane.
3.	Set the rest of the steel frame for the next level up.
4.	Install temporary erection cable bracing and/or vertical braces.
5.	Plumb and square the frame by whacking the bottom of the column with
a sledge to move the bottom in place.  Plumb the frame by a combination of
rocking the column on the shim stack, tightening and loosening the nuts from
the top, and adjusting the bracing.
6.	Grout the base plate.

If additional stability is required during construction the iron workers
drive wedges in the sides of the base plate.

Regards,
Harold O. Sprague

> -----Original Message-----
> From:	EphHirsch(--nospam--at)aol.com [SMTP:EphHirsch(--nospam--at)aol.com]
> Sent:	Wednesday, February 27, 2002 12:01 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Re: Levelling plates or shims ?
>
> To Harold Sprague's response I would add a suggested modification:
>        Rather than use shims under the base plate, use a double levelling
> nut                  procedure, whereby nuts are placed under the base
> plate which allows more accurate levelling as well as clamping action to
> secure the base plate and column when the above-plate nuts are installed.
>
>
> HTH,  Ephraim G. Hirsch, SE

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