At 20:50 09/04/2005, N4NM wrote:
>Yeah. As I recall, the last such thread was triggered by someone wanting
>to guy a crank-up. It morphed into a general discussion on any guyed
>self-supporters. As I recall, Yuri finally quenched the issue by making
>the distinction between cable-dependent crank-ups and non-cable-dependent
>(ratcheted) or fixed self supporters. It would appear from all those old
>posts that leg failure in compression would take a back seat to other
>possible failure modes such as section interfaces, dynamics, and all those
>other issues that require more than simple static analysis. There seemed
>to be a consensus that guying a cable-dependent crankup was probably a bad
>idea, but that certain fixed self-supporters might benefit. Proving it,
>however, would not be a trivial task, which is probably the reason most
>manufacturers avoid the issue even though their towers woud 'appear' to be
>capable.
>
>All that still leaves us back at the "analyze it if you have the
>credentials, or pay someone else who does; otherwise do what the maker
>says" point. YMMV.
>
>Chuck, N4NM
I'm not an engineer but the analysis is relatively straightforward. It's
easy to 'simplify' the structure and see what is actually happening in high
winds. (As a mathematician I'm more interested in proving the existence of
solutions rather than actually finding them!)
For the experts to suggest that guying a self-supporting fixed tower will
result in leg failure under compression (assuming sensible guying) is
untenable.
In the case of cable dependent crankups, sensible guying can still prove
advantageous. My own, cable dependent, crank up is rated, by the
manufacturer, (mindful of the prime directive) for a horizontal headload of
145lbs (sic) in a 100mph wind while un-guyed and 880lbs in a 100mph wind
when guyed.
Chris
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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