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Re: Levelling plates or shims ?

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By gosh, the rate of valid replies is going WAY up today!

Yes, by FDOT mandate the ASTM A325 bolts are hot dipped galvanized.  As far
as fatigue, I think we really see more of an issue in the arm-to-upright
connection (and also in the arm just beyond the connection) than in the
actual anchor bolts.

I've not tried to become familiar with the new AASHTO spec for signs, light
structures, etc., but I believe it has some provisions to address fatigue.

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 3:00 PM
Subject: RE: Levelling plates or shims ?


> 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
> >
>
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