On Jan 9, 2006, at 5:32 PM, Thin Air Communications wrote:
> 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.
While EMT may LOOK sturdy, it is NOT a structural material. That
said, I have used a 10 foot piece of 1.5" rigid EMT with an
additional 12" steel nipple to support a Cushcraft R7000 at 8 feet.
(eg 3 feet embedded in concrete)
Despite it's thickness, EMT is a pretty wimpy steel. Certainly not
nearly as strong as chrome-moly steel. However, I could see using
even a stout chrome-moly tubing (not PIPE!) wouldn't go more than
20-30 feet without requiring guying.
If you want something freestanding, you should go with a tower
designed to be freestanding. Even Rohn 25 can't be freestanding more
than about 30-35 feet.
Since you've gotten away with less, consider yourself lucky. If your
wire support happens to fall and isn't built to sound engineering
standards, you may find yourself liable for any damage it may cause.
Build it right, and you won't have to worry.
Bill Coleman, AA4LR, PP-ASEL Mail: email@example.com
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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