[TowerTalk] TowerTalk Digest: Using Double Wall EMT for wire support

[Thin Air Communications]

Hello TTians

I am considering using some thick wall (rigid) EMT for supports for an 800'
wire loop skywire. I currently am using ornamental steel that extends to
50'. The steel has not yet collapsed but the masts have become bowed due to
high winds and I don't have the real estate to guy it properly. So I am
looking at thick wall EMT also known as rigid EMT. I have heard of people
using this same stuff to 40' but I haven't heard of anyone going beyond
that. Ideally for the topband I'd need to be quite tall with 100' as a
minimum but I've already figured I'd have to settle for less. 

The pipe is galvanized steel and is twice the thickness of the ornamental
steel I currently am using. The pipe slides into each other but not tightly
so I'd have to shim then weld the mast together. The sizes that are
available at my local big box home store are 2", 1-3/4, 1-1/2, 1, 3/4 and
1/2". I would be using 4 10' sections on the bottom with 2" then
progressively step down for each additional 10'. I wouldn't use the 1/2" at
all. So I should have 40' in 2" and 10' for each size there after. So
40+10+10+10+10 = 80' possible. So my dilemma is, is this stuff structurally
sound enough to go to 80' I have doubts. I would weld all the joints. But
what would you think to be reasonable maximum with this stuff? I have mast
bases already set in the ground with a lot of concrete and the bases have a
pivot point as well as an up and out tie point for using a come-a-long to
winch the mast erect.

The winds we get here can be substantial. The last 2 storms brought winds
over 50mph sustained.

Thanks!

Michael J Wood
KE7ENC