Michael:
My handi-dandi black magic spreadsheet tells me that if the guy point
spacing on Rohn 55g is 40',i.e., guy poinst at 40', 80' and 120'. The
maximum axial capacity of the 55g is 43,500 pounds. This is without any
moment or shear loads, just pure axial load capacity. Moment will reduce
this number due to combined stress effects.
The increase will most likely be ok as far as the tower section is
concerned. I would be careful about the capacity of the tower base
foundation, especially if it was designed for the smaller axial load.
Actually the number of guy points required is a function of both the
axial load, wind moment in tower section and distance between guy
points.
There is no need to beef up the lower guys because you are using a
larger guy higher up. In practical terms the added vertical load does
not increase and load required to keep the lower guy points in plumb.
Hope this helps...
Hank Lonberg P.E.,S.E. / KR7X
Michael Rauh wrote:
>
> Hello All,
>
> My tower plans call for 11,200 lb Phillystran for the top guys. I've been
> offered 27,000 lb Philly. Questions:
>
> 1. Do I need to pretension the 27,000 lb breaking strength Phillystran to
> 2,700 lbs (10%)?
>
> 2. This will add 3X 0.707 X 1600 = 3400 lbs of base reaction to my system,
> right? (Top guy is at 45 degrees).
>
> 3. The tower is 120 feet of Rohn 55G. There are tree tiers of guys. I
> calculate the base reaction to be about 7500 lbs. So if I increase to
> 10,900 lbs what happens? The 55G is undoubtedly good for the extra load at
> the base, but do I need to beef up the lower guys to hold the tower in
> column with the extra load? Or to put it another way, how does one decide
> how many tiers of guy are needed and what the loads on the lower guys will
> be?
>
> Can anyone out there help me understand how this works?
>
> Mike Rauh, NV7X
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