Only the first of the quoted sentences are attributable to UST, the
second is my conclusion.
I have to agree that friction in the joint is good, but wonder if
tensioning to the rated torque (1000+ ft-lbs) for the bolts has a risk
of distortion that may cause functional problems. After all, the base
and tower are weldments which will have some distortions built in. When
I checked some bolt torques on my other tower tightened by "stronger
than average person using standard 1 1/2" combination wrench" I found
that they were tight, + or - a bit, to the 130 ft-lbs I was applying
with a torque wrench to tower 2. btw it took 4 cycles of tightening to
have all four bolts click at 130 ft-lbs without any motion.
There should be some clearance to get the bolts into the holes. I
didn't measure the hole diameters prior to engaging the bolts. Each
bolt had to be threaded into the hole in order to go through since the
holes were significantly mis-aligned. My guess is after 4 bolts are
installed and tightened there is so little clearance that the tower
can't rock more than a few thou up and down even if the flange gap is
still open. So, while I could measure the up/down motion with a dial
indicator, the 4' level I plumbed the tower with won't detect it.
The calcs show the base reaction moment as 80,000 ft-lbs, (EIA-222-F
85mph 3 sec gust, exposure C) so four 1" A325 bolts handle that.
However, the 1/2" thick A36 flanges bear on fully threaded bolts so
there could be some wearing down of the threads (and/or enlarging of the
holes) and a subsequent increase in clearance. So again, joint clamp
friction is helpful/necessary.
This whole (black hole?) thing started when I overheard some iron
workers talking about torque settings for 3/4" A325 bolts at 380 ft-lbs
and that got me to wondering....
73,
Grant KZ1W
On 10/13/2011 2:35 PM, knormoyle@surfnetusa.com wrote:
> This can't be right:
>
> "I probed a bit and he said that the design depends only on the shear
> strength of the bolts, not the clamp friction. So, as long as the bolts
> don't fall out they should withstand the base reaction forces."
>
> there is clearance between the bolt and the hole, right? So if there was no
> friction, the tower rocks in the wind.
> this leads to fatique failure of the bolts.
>
> So: there is a friction requirement.
>
> I think the weasel wording is that there's friction requirement for typical
> winds. But that for 70mph, they don't care if the tower shifts at
> the bolts.
>
> but after a big wind, if the tower is now slightly tilted due to a shift, do
> you fix it?
>
> Or are they saying the hole vs bolt diameter is close enough, that no
> shifting occurs, regardless of friction?
>
> -kevin
> ad6z
>
>
> ------- Original Message -------
> > From : John Hudson[mailto:jd_hudson@comcast.net]
> Sent : 10/13/2011 1:15:33 PM
> To : towertalk@contesting.com
> Cc :
> Subject : RE: Re: [TowerTalk] TX-455 holes
>
> Grant, I don't remember what type of bolts where on my tower but they did
> not "look" to as heavy duty as the old bolts I had. I was worried about
> breaking them off. I know I'm no were close to the 350# as KJ6Y states he's
> required and I'm sure I can tighten them more. We have no requirements on
> towers, YET, in western Ky. As far as "weasel wording" I've got whole other
> story about UST and their weasel wording.
>
>
> Thanks
>
> 73
> John
> KO4XJ
>
>
> -----Original Message-----
>
>
> Answering one of my own questions:
>
> I called UST and got through to Remi/Remy ?? the engineer. He said "the
> flange bolts should be tightened as much as the average person can
> tighten them with an average wrench".
>
> Wow - more "weasel wording" per K7LXC.. they used to have a spec, but
> withdrew it.
>
> I probed a bit and he said that the design depends only on the shear
> strength of the bolts, not the clamp friction. So, as long as the bolts
> don't fall out they should withstand the base reaction forces.
>
> I've torqued my flange bolts to 130 ft-lbs and that almost brings the
> flanges into tight contact.
>
> Grant KZ1W
snip...
>
>
>
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