jfleming@shelbynet.net wrote:
>
> > For towers that have 3 guys, do you give any consideration to the direction
> > of the predominant winds? For example, awould you try to orient the tower
> > so that the "2-guys" are into the wind?? I'm planning a 70 ft Glen Martin
> > - It will be assembled on the ground, then tilted/pulled into position. I
> > might have to orient the base such that I can get a rope from the tower
> > toward the nearest tree to aid getting it upright. If I end up NOT having
> > to do it this way, are there any theories affecting the orientation?
K7LXC@aol.com wrote:
> I would let your practical considerations dictate where the guys go.
> Your windspeed zone is only 70 MPH so you aren't subject to extreme winds.
>
> In general, towers legs fail in compression so if it was a real
> consideration you might want a tower face looking into the prevailing wind so
> that there are 2 guys generally in the windward direction. For a 70 foot ham
> tower, it really doesn't make any difference.
>
Hi Steve and John, Greetings to All,
Sorry to be slow in responding, too many balls in the air around here!
Just put in a 36 hr workday. Good contest training! The America's Cup
yacht race is a "Once in a lifetime experience" that comes around every
3-4 years. Currently enjoying my 4th "Lifetime Experience!" It's like
the month of May at the Indy 500, except it lasts for close to a year.
We're about 2 months away from three months of qualifying races with
three different U.S. based teams. It's the race to the race!
On this subject:
I don't think the above explanation agrees with what I have seen
modeling guyed Rohn towers. Nothing here to start a big debate over,
just a little bookeeping.
I'd agree with Steve, that if the tower is designed to meet the 70 Mph
basic wind speed (or higher), John can put the guys where he pleases.
Comments:
Item #1 - There is a bunch of detailed information regarding this
subject at the URL below. See the "Guyed Tower Study" link. Send me your
questions directly if the information is not making sense. I put the
stuff on the website to help answer these kinds of questions.
Item #2 - Does it make any difference which way the tower and guys are
oriented to the wind?
Depends on what we mean by "making any difference."
If building entirely within a spec, it shouldn't matter, because the
design should have taken all load cases into account.
Do the the guy loads and tower stress change with orientation (John's
question)? YES!
For towers guyed three ways and planted in rigid base connections (pour
concrete around tower stuck in hole):
Guy loads are highest with the wind 30 Deg from a guy anchor (regardless
of base connection). Tower section combined stress is highest when the
wind is between two anchors. Guy loads are least in this load case
(regardless of base connection). Tower combined stress is least with the
wind in line with one guy anchor.
Is one situation preferred over the other?
It depends on what is limiting the tower design, guy loads or tower
loads.
If I was worried about tower legs failing, I'd make the wind blow in
line with any guy anchor.
If I was worried about guy cables failing, I'd make the wind blow
perpendicular to any tower face.
This can be understood by reviewing the "Guyed Tower Study."
Item #3 - Does any of this really affect how most guys install their
towers?
No!
Building within the confines of an established specification is the most
expedient and prudent thing to do.
Item #4 - Always a popular one cuz it shows up so often! Can an existing
canned tower design carry more load?
YES!
The existing tower design spec's have ample safety margins! They're
supposed to be that way!
Overloading the existing design errodes the safety margins. Remember,
the designs are based on survival of infrequent (like 50 year) wind
events, with allowance for long term deterioration in components of the
system.
You can always take matters into your own hands and gamble on when that
event might occur!
YOYO here! All you need to decide is when the long term severe wind
event will occur and what condition your system will be in when it does
occur!
Try 1-900-Psycos-Are-Us for your free reading! If they're any good, and
can't tell you when your tower might fall down, at least ask when your
rotator will fetch up, or the next lightning strike will occur! :-)
The answer is Yes, If one changes the tower configuration.
Going beyond the canned designs requires a bunch of analytical work and
significant configuration changes that can yield some spectacular
results!
Don't try this at home without some adult supervision! :-)
--
73, Kurt
K7NV "That's K7 "Nevada" (ex - NI6W)
YagiStress - The Ultimate Software for Yagi Mechanical Design
Visit http://www.freeyellow.com/members3/yagistress/
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