[TowerTalk] Antenna spacing question
jimlux at earthlink.net
Wed Jan 27 07:03:28 PST 2010
TexasRF at aol.com wrote:
> Hi Jim and Pete, measuring the deflection of a mast is not the data that
> matters in wind survival. With a given diameter and wall thickness, the
> deflection will be about the same for all steel alloys.
> What is needed is the stress that will be applied so it can be compared
> with specifications of the material used. Measuring the stress is not a home
> project but we have plenty of computer software available to accurately
> compute the stress.
An interesting point.
If you do the horizontal test, and load it to your design load, and it
doesn't "fail", then, hey, you know that your design load is less than
the failure load. You just don't know by how much.
And, as pointed out, the deflection is more dependent on the modulus
(stiffness) of the steel, and they're all about the same.
If you want to test empirically, you can either do a "proof test", where
you load it with something MORE than you expect (say, twice) and verify
no failure, or you can load an identical unit to failure, and then
you'll know how strong it is.
The challenge with the load to failure is "how do you know the test
article is *identical* to the real thing?", so you have to either do
many tests (to get some statistics on variability) OR you make the
failure test a preparation fora proof test (e.g. if your design load was
100 lb, and you failed at 300 lb, then you can feel relatively confident
that your proof test at 200lb for the real item is reasonable.
For one-offs that aren't close to the edge in performance, proof tests
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