D Calder wrote:
> It wasn't fence material but it wasn't enough for hurricane Charlie either!
> I do have something
> stronger up there now. Now the weak link will be the antennas. HI
>
Or the tower?
73
Roger (K8RI)
> 73 Dave n4zkf
>
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of Julio Peralta
> Sent: Friday, March 19, 2010 4:53 PM
> To: 'Tower and HF antenna construction topics.'
> Subject: Re: [TowerTalk] 2" masts.. an eye opener !
>
> Looks like what happened when I used the fence material.
>
> Julio, W4HY
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of D Calder
> Sent: Friday, March 19, 2010 8:20 AM
> To: 'Tower and HF antenna construction topics.'
> Subject: Re: [TowerTalk] 2" masts.. an eye opener !
>
> Here is what "cheap mast" pipe did to me when the eye of Charlie came over..
>
> http://www.n4zkf.com/files/Tower.jpg
>
> I have since went to steel and it's done well.
>
> The TV antenna mounted to the power weather head in the foreground, it's me
> but a moron neighbor. FPL
> has since made him remove it.
>
> 73 Dave n4zkf
>
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of Jim Thomson
> Sent: Thursday, March 18, 2010 2:04 AM
> To: towertalk@contesting.com
> Subject: [TowerTalk] 2" masts.. an eye opener !
>
> Date: Wed, 17 Mar 2010 18:42:35 EDT
> From: TexasRF@aol.com
> Subject: Re: [TowerTalk] 2" O.D. Pipe???
>
> hi Ted, you can find it at _www.texastowers.com_
> (http://www.texastowers.com) .
>
> Click on the on line catalog button and select steel masts.
>
> 73,
> Gerald K5GW
>
> ## I used the arrl mast software, available free online at
>
>
>
> http://thebont.com/spreadsheets/AnalysisOfAntennaMastStrength.htm
>
> Scroll down , till u get to 'download here' . This is from the 2004 ch-22
> of the arrl ant book.
>
> I got a REAL eye opener, when plugging stuff into it ! I'm stuck using a
> 2" mast on the HDX-689 I just bought, since conversion to 3" is a
> horror
> show. The PPM, bearings, etc, holes in plates, etc, everything is 2".
>
> That being the case, and wanting to install 3 x yagi's on the mast + a 80m
> rotary dipole, the 2" mast demands are enormous.
>
> I can get, locally, at any of our 4 x steel supplier's... 1026 DOM.. in any
> diam
> up to 12". All their 1026 DOM is the same... 75 ksi. AS sells 1026
> masts in 87 ksi.
> 4130 chromoly can be had in 104 ksi from AS...25" thick. 4130 chromoly in
> 106 ksi
> can be obtained from US Tower corp.... .375" thick.
>
> Check out the below calcs.
>
> 1.9" x .145" wall x 35 ksi = 42 mph [sched 40]
> 1.9" x .200" wall x 35 ksi = 47 mph [sched 80]
> 1.9" x .950" wall x 35 ksi = 60 mph [SOLID ! ]
> 2" x .25" wall x 75 ksi = 78 mph
> 2" x .25" wall x 87 ksi = 84 mph
> 2" x .375" wall x 75 ksi = 87 mph
> 2" x .25" wall x 104 ksi = 92 mph
> 2" x.375" wall x 106 ksi = 104 mph
>
> 104 mph / 92 mph = 1.13 1.13 x 1.13 = 1.28
> The .375" thick chromoly is 28% stronger, than the .25" thick chromoly.
> Pressure goes up to the SQUARE of the wind speed, regardless of whose
> formulae
> you use.
>
> Here in Canada, all new tower /mast specs/ ant specs are done in pressure
> [metric as well]
> Most are converted to mph as well.... so we can relate to it... [ and lbs
> per ft, etc]
>
> I just got yet 3 x more pix via e-mail... of masts folded right
> over...in the last 3 x weeks !
> Several more install's I have seen... are just an accident waiting to
> happen.
>
> This has been going on since 1972, when I got my ham ticket. Nobody seems
> to... 'get it'.
> No rocket science here. Yield strength x section modulus = max bending
> moment of a mast.
> B4 pc's... I used a calculator by hand.. and the old EIA/rohn rs-222-C spec
> "70 mph = 19.6 lbs per foot"
> Calculate the Effective wind load of each yagi in flat plate eq. [
> projected area x .67]
> Effective Wind load x pressure = total force on yagi.
> Total force x height of yagi up the mast = bending moment at base of mast.
> Add in the bending moment of the mast itself.
>
> These days it's easier with the various spreadsheets. Now try and
> explain to joe ham the above,
> and they still won't believe it. Joe ham doesn't have a clue what the
> windload on his huge quad
> actually is. Any els that are either vertically polarized, or on an
> angle... have a huge windload.
> Point a vertically polarized yagi in ANY direction.... and the els are
> ALWAYS broadside to the wind !
> Same deal with a quad. Now put the boom of the quad broadside to the
> wind... yikes look out.
>
> Mast selection is not to be trifled with. Removing a bent mast is extremely
> dangerous... esp with
> ants still on it. In some cases a crane can't be brought in.. due to
> power lines, etc, etc. You take
> a heavy mast, loaded with ants... and it snaps off.... it can easily slice
> polygon rod + Phillystran ..
> then down comes the entire tower!
>
> later......... Jim VE7RF
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