Return to index: [Subject] [Thread] [Date] [Author]

RE: Levelling plates or shims ?

[Subject Prev][Subject Next][Thread Prev][Thread Next]
David,

These structures are different.  You have access to the bottom nut, they are
light weight, and they are generally isolated and not dependent on other
columns (for relative elevation).  There is nothing wrong with leveling nuts
in those applications.

I would caution however that in the high winds (that you get down in your
neck of the woods) to take into account the fatigue on the reduced section
of the anchor rod.  You can't preload to avoid stress cycles.

The Australians did a study for glazing a while back that said for one given
storm, they could get 10,000 cycles on elements.  This is the study that fed
into the impact resistant glazing performance requirements.

I would also urge caution on galvanizing high strength bolts.  You can
create a problem for hydrogen embrittlement.  This is not a pleasant mode of
failure.  There is no warning.

Do you hot dip galvanize the bolts in Florida?

Regards,
Harold O. Sprague

> -----Original Message-----
> From:	M. David Finley, P.E. [SMTP:pec(--nospam--at)isgroup.net]
> Sent:	Wednesday, February 27, 2002 2:04 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Re: Levelling plates or shims ?
>
> Harold,
>
> The problems and procedures you described obviously apply to building
> columns.  Would they also apply to traffic signal structures (mast arms,
> cantilever signs, span signs, etc.)?  These are probably much lighter than
> the column sections you are probably talking about.
>
> I ask because we commonly show leveling nuts for these traffic structures,
> but never get any feedback as to how well they work.
>
> FWIW, the grout pad thickness is usually 1.5 times the anchor bolt
> diameter
> and the nuts are all specified to be heavy hex.  We normally specify a
> minimum of 6 anchor bolts (circular bolt pattern).  The structures are
> being
> set on drilled shaft foundations that may be at ground level or elevated
> slightly above the surrounding grade.
>
> M. David Finley, P.E.
> Lake City, FL  32025
>
> ----- Original Message -----
> From: "Sprague, Harold O." <SpragueHO(--nospam--at)bv.com>
> To: <seaint(--nospam--at)seaint.org>
> Sent: Wednesday, February 27, 2002 1:39 PM
> Subject: RE: Levelling plates or shims ?
>
>
> > 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
>

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
*
*   This email was sent to you via Structural Engineers
*   Association of Southern California (SEAOSC) server. To
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
*   send to the list is public domain and may be re-posted
*   without your permission. Make sure you visit our web
*   site at: http://www.seaint.org
******* ****** ****** ****** ******* ****** ****** ********