I am reluctant to extend this thread...but there's a flaw
here, imho. I'll make this my last on the topic:
Chris wrote:
I beg to differ. The function of sensible guying is to prevent the tower
from reaching its material failure point, or at least delay it.
>The function of the guys, is NOT to add strength to the
>system. The function is to force a different failure mode,
>and the price of doing that will be reduced load rating, or
>earlier failure,
on the contrary, the function of guys IS to make the system stronger. After
all, you do guy Rohn 25/45/55 don't you? Sensible guying here, and
elsewhere, will increase the load rating and produce later failure.
-0-
No argument about "sensible guying".
The initial post concerned tower FAILURE, not the value of guys vs. no guys.
The function of a "safety guy" in the specified situation was to keep the
tower from hitting the power lines, if it fell. i.e. to CHANGE the failure
mechanism.
THAT SAID, a few short comments:
* if you're going to guy it anyway, why bother with a self-supporter?
save the concrete expense! (WB9CRY's point)
* HBDX towers were designed for small loads, like TV antennas. They are
NOT specified to hold anything with a boom longer than 12'.
* HBDX towers, or look-alikes, with tapered, bolted, stamped-metal legs, are
considerably
weaker than uniform cross-section, tubular legged towers with welded
cross-bracing.
* If you guy an HBDX or look-alike, you are imposing compressive loading on
the smaller top-sections, which may not be designed to withstand it.
So where you guy the tower, and how, may actually cause earlier failure.
* I intuit a failure mode where a gust imposes rotational load at the same
time
as peak compressive load, resulting in a spiral, folding failure
somewhere
in the mid-section. (just above the mid-guys?) But without knowing the
design
numbers and the dynammic reserve in same, all our words are just
that.....
Did anyone mention the value of adding torque bars?
* Back to the original post...this was a safety and liability question which
went astray.
Only a structural engineer can satisfy building code requirements for
a modified structure as proposed. I have difficulty believing that a
permit
would be granted for a tower without safe fall distance to the power
line.
I have difficulty, as well, believing that any insurance company would
cover
the liability. This has "bad idea" written all over it.
n2ea
jimjarvis@ieee.org
_______________________________________________
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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