In a message dated 5/19/2010 12:01:39 P.M. Pacific Daylight Time,
towertalk-request@contesting.com writes:
> Can anyone help me out? I am in the process of putting up a 85' tower.
I am presently looking into guy wires. The calculated maximum force on the
guy wires is 2990 lb. I decided that 5/16" EHS 1x7 wire should be fine.
Now when I receive quotes I find various grades (if the quoter even knows
what grade it is). Can somebody explain what the difference is? I see that EHS
is recommended by most tower manufacturer but why?
> The strength of the different grades are mind boggling:
> For 5/16" galvanized steel wire I have break force for:
> Common Grade 3200
Siemens Martin Grade 5350
High strength Grade 8000
Extra High Strength Grade 11200
Utilities/Specification Grade 18000
Howdy --
I'll bite. What kind of tower is it? What does the manufacturer say
about it? Why did you decide on 5/16" guys? Are you an engineer?
> One of my questions is:" Can I use 9/32" Utilities Grade (11500 lb)
instead of 5/16" EHS (11200 lb)? 11500 lb seems OK for a maximum expected
force of 2990 lb (120 mph wind)? What would happen if I use 5/8" Common Grade
(11600 lb)?
> Could I possible use 1/4" Utilities Grade (6000 lb) or is that to be
too close to the maximum force (2990 lb)?
These are engineering questions. If you're an engineer, feel free to
do the calcs yourself. If not, follow the LXC Prime Directive to "DO what
the manufacturer says" or get an engineer to run the calcs.
Something you'll have to deal with is guy wire terminations. Nowadays
everyone uses Preformed Guy Grips and you'll have to get the exact grip for
the guy wire that you're using. You CANNOT interchange Preforms on the
same size guy wire material.
Why reinvent the wheel? Tower manufacturers specify EHS for good
engineering and industry practices (e.g. TIA-222 Tower Standard). I think
you're
making this more difficult than it is.
Something else you have to account for is guy tension. The bigger the
guy, the bigger the tension. And the bigger the tension, the bigger the
compressive forces on the legs. With guy wires that are too big, the initial
tension may reduce the tower capacity dramatically. The strength of a tower
is leg capacity and it's got nothing to do with what guy wire you use.
DO what the manufacturer says. Or have an engineer calc it for you. In
the absence of that, you can make some educated inferences from similar
Rohn towers and their specs.
Cheers,
Steve K7LXC
TOWER TECH -
Professional tower services for hams
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