[TowerTalk] [Bulk] Re: MASTS

[Jeff AC0C]

What is possible in the worst case and what is likely seem two different 
things.  I've not seen EMT do anything other than just bend (which it does 
pretty easily) and buckle (if you really really abuse it).

So while I can imagine a scenario where the beam is bent back and forth by 
alternativing massive blasts of wind resulting in a buckle being introduced 
on both sides of the mast - eventually causing it to break and the thing 
flying off, that seems pretty bizarre.  The more likely case is that it will 
just bend - and a guy will look out his window and wonder why his beam has a 
big tilt that was not there before last night's storm.

73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie

-----Original Message----- 
From: Grant Saviers
Sent: Tuesday, March 15, 2016 8:40 PM
To: TexasRF at aol.com ; towertalk at contesting.com
Subject: Re: [TowerTalk] [Bulk] Re: MASTS

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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