[TowerTalk] FW: Anchor Bolts US Tower

[KM5VI]

Bolt failure theory and the engineering design of bolted connections
differentiate connections by how the load will be transferred though the
connection.  "Slip-critical" class connections rely on friction developed
between the connection members to transfer load.  This friction is produced
by the compressive forces in the connection requiring the bolt to be torqued
to a design specification.  "Shear" connections rely on the shear strength
of the bolt to transfer load and need only to be "snug tight".  Either class
of connection is suitable for tension loading.

Wind loads transferred to the anchor bolts by a tower are overwhelmingly
tensile in nature with a relatively small shear component.  The bolt size
required to safely handle the tensile loads result in shear stress levels
that can easily be handled by a shear type bolt connection, thus the design
of tower anchor bolt connections are typically not required to be
slip-critical.  Therefore snug tight is typically adequate for this type of
application.

KM5VI
Matt Flukinger, PE



-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Grant
Saviers
Sent: Tuesday, September 04, 2012 11:08 PM
To: Brad L. Tracey
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] Anchor Bolts US Tower

My experience with a new steel structure was quite different.  All heavy 
structural ("red iron") steel to steel bolts were tightened with a 
torque wrench.  In some cases to 200 ft-lbs for the A36 fasteners.  It 
took two guys and a big torque wrench.  In fact a special inspection was 
called out by the building permit.  (King Cty, WA)

For the structure to footing embedded bolts, I think "snug" is the 
appropriate description.

I hadn't seen the UST FAQ when my HDX589's went up so called the factory 
and got the "snug" BS answer.  Portland Bolt has torque specs for 
different bolt grades, and the 589 leg to base bolts should be torqued 
to over 600 ft-lbs.  I stopped at 175 ft-lbs, which may qualify in UST 
engineering terms as "super snug".   It took several passes across each 
leg set to get all bolts to that level.  I checked them a month later 
and all were essentially unchanged.

Grant KZ1W


On 9/4/2012 9:45 AM, Brad L. Tracey wrote:
> 	I'm not going to get into the tower cable lubricate part of the
> group with US Tower. But to answer Jim's comment about snug fit. As a
> Commercial Contractor I build a lot of Pre-engineered building and the
> manufactures (Butler, Metallic, ect) and all of them say the same thing
> about their anchor bolts and bolts holding the buildings components
together
> and that is "turn of the nut method" or snug fit. Just meaning as tight as
> you can get with a standard wrench with using bare hands. I know it sounds
> silly but that is a very common practice in my line of work. Most of the
> engineers I work with agree with it to. I'm not trying to act like I agree
> with anything US Tower says or be rude to you but just wanted to let you
> know.
>
> Brad N3NRN
>
>
>
>
>   It would be nice if  UST provided detailed instructions on  how to
>> re-cable their towers.  They insist you recable their
>> towers, but then wont provide the info.   Check out their info on how
much
>> torque required for both the anchor bolts  +
>> leg bolts..... answer,  snug fit.   What kinda  BS  answer is that.
>>
>> Jim  VE7RF
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