[TowerTalk] Grout
Tower2sell@aol.com
Tower2sell@aol.com
Sun, 16 Jul 2000 16:23:31 EDT
Well Hank I was hoping to not have to get into all of the gory details of anchor bolt and base plate design because it is a very boring subject and will put most of the readers to sleep. So I'l generalize first.
The grout does effect the number of anchor bolts and thickness of base plate.
NOW ONLY THE ENGINEERING TYPES WHO REALLY, REALLY CARE TO KNOW THE WHY AND HOW NEED TO READ FURTHER.
The question was about a free standing tower with anchor bolts. This is a totally different animal than a building column base plate, which is similar to the base section of a guyed tower. I also made an assumption that the base plate was double nutted, and did not use shims.
My experience with shimmed tower base plates dates back to the '70. After removing a tower and examining the grout I found the grout was not uniform under the shimmed base plate and was mainly around the exterior. The base plate was essentially being supported by the shims. The construction department found shims to be time consuming and hard to install. Double nutted anchor blots were implemented. Since that time not personally seen any single nutted grouted anchor bolts (and hope I don't).
Now let get down to the nitty gritty of the question. How does the grout effect the number of anchor bolts and base plate thickness?
For a free standing tower the leg reaction will be a compression or tension and a shear. Engineers view the problem differently and the codes do not always help. The problem is how do you combine the shear and the axial load. I there is no grout, then the bolts will be in bending (V x H). If there is grout then the bolt bending issue is not a problem since the shear can be assumed to prevent bolt bending.
Now the base plate. There are numerous analytical methods for designing base plates and some of them use the clamping force of the plate to the grout to create a fixed end moment condition and reduce the plate thickness. (one of the problems with this assumption is that a reduced base plate thickness can cause prying action in the anchor bolts and increase the number of anchor bolts. A quick observation is that not all anchor bolt and base plates are designed 100% correctly, but I have never personally seen a problem with any of them. The question of grout depends on what the engineer's assumptions were and quite frankly I'm only a good guesser and a terrible mind reader.
Now the good news. A new revision of the ANSI/EIA/TIA-222-G is being written and will address the issue. I have heard that they are proposing to ignore the bolt bending issue if the height between the concrete and base plate is two bolt diameters of less. This should result in the elimination of the grout for free standing towers base plates. (assuming the original design permits)
ARE YOU STILL AWAKE? Then you must be an engineer.
Tower2sell@aol.com
In a message dated Fri, 14 Jul 2000 11:44:42 AM Eastern Daylight Time, "Lonberg, Hank" <Hank.Lonberg@Harrisgrp.com> writes:
<<
Our standard specs for grouting call for Five Star Grout and nobody seems to
have a problem finding it.
Grout does nothing to decrease the baseplate thickness or reduce the number
of anchor bolts. These are determined by the loads in the system and the
allowable loads that anchor bolts or steel plate can carry. What the grout
does is allow a system to be set at a precise elevation and plumb tolerance
using some leveling mechanism, shims or leveling nuts. The normal tolerance
to concrete placement is plus/minus 1/8 inch. The grout fills the space
between the formed and placed concrete and the underside of the base-plate
to transfer the load into the foundation, it is an extension of the concrete
to the underside of the plate and allow for uniform bearing by filling in
all the irregularities that may be present.
When you grout the base plate be sure to completely fill the space and
vibrate or bang the top of the plate so there are no voids under the
base-plate, and use a non-metallic non-shrink grout, metallic grouts tend to
discolor due to weathering if outdoors.
Hank Lonberg P.E. / KR7X
-----Original Message-----
From: Tower2sell@aol.com [SMTP:Tower2sell@aol.com]
Sent: Friday, July 14, 2000 5:28 AM
To: k0myw@worldnet.att.net; towertalk@contesting.com
Subject: Re: [TowerTalk] Grout
Grout under a base plate allows for fewer anchorbolts and thinner
baseplates. Non-shrink, non-metalic grout with about 5000 psi compressive
strength or more is good.
FIVE STAR FLUID GROUT 100 is a commonly specified grout but may not
be widely available. They have a web site with various types of grouts.
Normally a concrete supply company will carry this commercial grade grout.
Look for an equal.
Tower2sell@aol.com
In a message dated Fri, 14 Jul 2000 8:08:32 AM Eastern Daylight
Time, "Mike O'Brien" <k0myw@worldnet.att.net> writes:
<<
Please pardon my ignorance, but what exactly is the purpose of
packing
grout between a tower baseplate and the top of the concrete pad? I
know
that U.S. Tower, for instance, specifies it, but offers no
explanation
nor directions...
73, Mike, k0myw
K7LXC@aol.com wrote:
>
> In a message dated 12-07-00 4.23.31 Greenwich Standard Time,
kn9t@webtv.net
> writes:
>
> > Need some info on type of grout to use
> > under legs and around amchor bolts of free standing towers. Can
this be
> > purchased at the local home builders stores ?
>
> Look in the yellow pages under Masonry Supplies or a building
materials
> supplier. You're looking for non-shrink grout.
>
> I've also used the Home Depot type but it discolored after a
year or two.
> Works okay but looks pretty grungy.
>
> Cheers, Steve K7LXC
> Tower Tech
>
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