Date: Wed, 1 Jan 2020 11:13:16 -0500
From: Gedas <w8bya@mchsi.com>
To: TowerTalk@contesting.com
Subject: [TowerTalk] Which Vertical is More Robust ?
## Im sure aluminum EMT tubing is pretty soft stuff.
EMT is designed to be easily formed, bent, etc..with conduit benders.
##IF you know the yield strength of the proposed EMT,
plus the yield strength of the upper tubing, 6061-T6 is 40 ksi,
6063-T832 is 39 ksi. Then just stuff the proposed design
into DXEs handy ... yagi mechanical software. It will spit out
exactly how far it will deflect.....at any given wind speed, and
also what wind speed it will break at......and also WHERE it will
break.
## Ok, just checked, AL- EMT is 6063- T1. Thats super soft,
with a low yield strength. It will fold like an accordion. Dont use
it.
## design the entire proposed vert, using .120 wall 6061-T6
for the lower sections. Start with at least 2 inch OD at base,
and build the bottom sections using 6 ft lengths.
Like 2 inch, 1.75 inch, 1.5 inch, 1.25 inch Allow 3-6 inches for
overlaps, and use a pair of .25-20 SS bolts and nylocks..at
right angles for the splices. That gets you up to 23.25 ft .
Use 1 inch x .058 wall x 3 ft, then same with .875, 750, .5 inch.
## DXEs ..yagi mechanical is dirt cheap, easy to use, and dead
on accurate. Dont guess. It will also spit out deflection with
guys, like say 1 set of guys at 23 ft. Use the... no-spec windload
option,
thats what u get in a wind tunnel. U can also enter the yield
strength
for each individual section.
## section modulus x yield strength = bending moment, its that simple.
## software will spit out the weak points, which can easily be
beefed up
using doublers, triplers etc.
## Dont mess with galvanized steel EMT.
Jim VE7RF
<A) Starts out with a 10' length of 1-1/4" EMT followed by tapering 5'
<sections of aluminum tubing (4' long exposed, 1' inside the previous
<lower section) until the very top length section which will be 3/4" OD
<dia. These will be standard DX engineering aluminum tubes.
<B) Starts out with a 10' length of 1-1/2" EMT, then a 5' length of
<1-1/4" dia of EMT (4' long exposed, 1' inside the previous section of
<EMT) then followed by tapering 5' sections of aluminum tubing as above.
<The only difference being this choice would end up using 1" aluminum
<tubing as the very top piece.
<So the obvious difference between the two are that choice A) uses just
<one length of thinner EMT and overall thinner aluminum tubing sections
<to the top while choice B) uses 2 lengths of larger dia EMT and then
<larger dia aluminum tubing to the very top.
<I do not have the software to analyze choice A) vs. choice B) in a high
<wind situation. I am uncertain if the stronger, larger dia tubing with
<it's higher wind load will be a plus or a minus in the end to it's
<overall strength. Any thoughts or comments on which one will survive
<better during heavy wind conditions? TU
<Gedas, W8BYA
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