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Re: [TowerTalk] [Bulk] Re: MASTS

To: grants2@pacbell.net, towertalk@contesting.com
Subject: Re: [TowerTalk] [Bulk] Re: MASTS
From: TexasRF--- via TowerTalk <towertalk@contesting.com>
Reply-to: TexasRF@aol.com
Date: Tue, 15 Mar 2016 22:39:49 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Hi Grant, when I did a google search for "EMT yield strength" a reference  
came up with the 35000 psi yield number. I didn't notice that the actual 
product  was called IMC which is not the same thing at all.
 
You are quite right in your comments and the wind survival numbers I  
offered should be disregarded.
 
73,
Gerald K5GW
 
 
 
In a message dated 3/15/2016 8:40:24 P.M. Central Daylight Time,  
grants2@pacbell.net writes:

Gerald,

Could you point me to the 35kpsi spec?  I  couldn't find a steel spec on 
the Wheatland EMT manufacturer site, or that  matter on any other site I 
looked at that google turned up re conduit  specs.

Here is a section from a Q&A by the Steel Tube Institute re  the 
controlling ANSI 80.3 standard for electrical conduit

"Rigid  conduit is intended for electrical applications, not structural 
ones. Its  requirements are governed by UL and ANSI specifications, not 
by ASTM. The  main issue here is that, whereas dimensions may be similar 
between the  two, rigid conduit is not intended for, is not designed for, 
and is not  tested for any strength or structural requirements."

So while the yield  number and wall thickness in the mast calculator turn 
out ok, YMMV.   And likely with the thin wall it will deform with boom 
and rotator  clamps.

Standard schedule 40 water pipe would be a much better choice  for 
several reasons:

1. the grade steel is specified
2. it is  specified to withstand an internal pressure, which is a control 
on the  seam weld quality
3. it is allowable in structural applications, although  used mostly in 
larger diameters.
4. hot dip galvanized inside and  out

Caveat emptor.  Unless it falls down, and your insurance asks  about the 
engineering and the plaintiffs attorney finds the statement to  the 
effect "I don't care if it falls down."

Grant  KZ1W


On 3/15/2016 12:35 PM, TexasRF--- via TowerTalk wrote:
>  Google says 1.5" EMT is actually 1.75" OD and .065" wall thickness and
>  yield strength is 35,000 psi.
>   
> Putting these  numbers in a mast analysis program and using a 7 sq ft wind
> load 24"  above top of tower, failure happens at a wind speed of 84 mph.
>  Lowering  to 12" above tower top, failure is at 119  mph.
>   
> So, it could be useful in a modest  installation.
>   
> 73,
> Gerald  K5GW
>   
>   
>   
> In  a message dated 3/15/2016 2:01:59 P.M. Central Daylight Time,
>  infomet@embarqmail.com writes:
>
> Let’s  not call  names.
> An EMT mast is great, as long as you don’t get greedy and   make it too 
tall
> outside the tower.
> Mine is about 2’ above the  tower top  and I think it will survive any 
wind
> likely in my  area.  And I really  won’t cry if the $150 beam is damaged!
>  It’s several years old and shows no  sign of deterioration.  It cost  
almost
> nothing and weighs next to  nothing.
> So I have a  used tower, used tribander, used rotator, EMT mast,  but new
>  coax.
> I also have a HB amp made from used components, with an  easy  KW+ output.
> It’s a rare pileup I can’t get through.
>  I am VERY happy,  but may change to an LPDA so I can get the WARC  bands,
> someday.
>
> I also  use junk tubing from a  kid’s swingset for Field Day.  It’s 
worked
> fine  for a  decade or so.
>
> Successful systems can be designed around most  any  components, as long 
as
> one doesn’t try to do too  much!
> I’d far rather see a  ham put up 30-40 feet of used tower  and a used
> tribander than envy those with  more elaborate,  expensive setups!
> A few more hours on the air will make up  for a  few dB of antenna
> performance and there will be money left for   beer.
>
> Wilson
> W4BOH
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