[TowerTalk] 2" masts.. an eye opener !

Roger (K8RI) K8RI-on-TowerTalk at tm.net
Fri Mar 19 14:41:53 PDT 2010



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 at contesting.com
> [mailto:towertalk-bounces at 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 at contesting.com
> [mailto:towertalk-bounces at 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 at contesting.com
> [mailto:towertalk-bounces at contesting.com] On Behalf Of Jim Thomson
> Sent: Thursday, March 18, 2010 2:04 AM
> To: towertalk at contesting.com
> Subject: [TowerTalk] 2" masts.. an eye opener !
>
> Date: Wed, 17 Mar 2010 18:42:35 EDT
> From: TexasRF at 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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