Comments inserted:
kr7x@attbi.com wrote:
>
> Talkians:
>
<snip>
>
> Neither material has a greater propensity for fatigue
> than the other.. properly designed.
Believe I said something to that effect.
>
> Other comments:
>
<snip>
>
> Most catastrophic tower failures occur due to
> compression buckling of either a tower leg or brace.
Believe I said EXACTLY that.
>
> There is no progressive derating of any structure.
>
> There is, in my experience, no such animal as:
> Coefficient of Flexation. Maybe the Modulus of
> Elasticity is what the person meant.
My engineering education was begun 47 years ago [and ended 44 years go!]
.. that's the term I was mentally searching for!
<snip>
> Any metal that is loaded below its threshold fatigue
> stress level and unloaded can,theoretically be loaded
> and unloaded forever...
>
> Rule of thumb is to use one half the yield stress of the
> material, this keeps the stress well within the elastic
> range for the material.
>
> The question of using a steel or aluminum tower of
> comparable load carr[y]ing capacity is not one of which
> will fatigue before the other but one of enviromental
> corrosion resistance, weight, transportatability,
> absolute strength, size of structure required and cost.
> All of these vary for each material, intended usage and
> total load carrying requirements.
And, for my situation, the aluminum tower was less expensive for the
same 'bang for the buck'.
>
> I have at various time designed aluminum, steel, fiber
> reinforced composite, and timber structures to support
> elevated loads of, freestanding and guyed, antennas and
> other equipment. The decisions were never based on the
> fatigue preformance of the materials but rather on cost,
> availability, transportation, and future expandability
> of the proposed structure.
Again .. for my situation, those factors considered .. I chose aluminum.
>
> As we contribute to this reflector, we as individuals
> need to consider what we are saying and what factual
> basis we are using to support our statements.
I totally agree! If I made statements of opinion, not fact, then I was
wrong.. but I repeat .. in my situation .. aluminum gave more for less.
Don Havlicek, B.S./M.A./A.B.D. [Math], (A.B.D. = "All But Dissertation")
N8DE
> Hank Lonberg, P.E./ S.E., KR7X
>
> ________________________________________________________________________
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