[TowerTalk] [Bulk] Re: MASTS

[Grant Saviers]

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 at 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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