[TowerTalk] TX-455 holes

[Grant Saviers]

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 at 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 at comcast.net]
> Sent    : 10/13/2011 1:15:33 PM
> To      : towertalk at 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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