>
>Perhaps I'm missing something here. You guys ought to know all this
>better than me, a tower newcomer. The rough answer is that the rated
>load at 70 mph is 50% of the rated load at 50 mph. Wind loading is
>proportional to the square of the wind speed.
>
>With this approximation, rated load at 80 mph is about 40% of 50 mph spec,
>and rated load at 90 mph is 30% of the 50 mph spec.
I think you are missing something here, Nick. When you read the specs for
loads that can be put on a tower, the load of the TOWER ITSELF is not
mentioned, but it certainly is there. So when you see a spec that says
"this tower will take 18 square feet at 50 mph" it really means "this tower
will support itself plus 18 additional square feet of load at 50 mph". This
is important since if you remove half of the 18 square feet of additional
load, you STILL have the ENTIRE load of the tower itself to support. You
have to remove a lot more than half of the 18 square feet to remove half of
the entire load.
Suppose, for example, the tower itself represents a load of 18 square feet.
The additional 18 square feet of load on top is only HALF of the total load.
So to reduce the total tower load to half, you have to remove ALL of the 18
square foot load on the top.
>If you want to get the right numbers, ask the tower manufacturer for
>the engineering docs and figure it out yourself for whatever wind
>speed you like. I have a US Towers 89' crank-up and have been through
>the engineering docs - I think the rating is actually better than
>they advertise.
It should be since they should include a safety margin . . .
It seems to me that to do the calculations including the load of the tower
itself, you would need to know the square footage of the extended tower with
no other load on it. I have never seen any figures on this from any crankup
tower manufacturer. But then I have to admit I have never asked for them,
either. For me, it would only be an acedemic exercise because I will NEVER
own a crankup based only on the sheer number of devastating accidents with
them. BTW, these crankup catastrophes do not just happen to inexperienced
newcomers . . . they happen to guys that have been installing and using
towers for decades.
Stan w7ni@teleport.com
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