Your "problem" (not sure you have one) is the difference in stretch of
the Phillystran vs EHS. Adding more tension to the Philly helps that a
bit, but at the cost of a lot more column load on the tower. Doubling
the Philly or going up a size yields less stretch and in what the tower
can stand for wind load.
Take a look at the K7NV analysis of tower guys - it is very instructive
about what is going on in a tower with mixed guy materials at
http://wiki.contesting.com/index.php/Guyed_tower_study That analysis
shows that your pier pin base is a real plus.
Grant KZ1W
On 5/9/2011 9:50 AM, Pete Smith wrote:
> I have a 97' Rohn 25 tower mounted on a pier pin. The guys are at 92,
> 61, and 31 feet above ground. The tower has 2 C-3E tribanders at 69 and
> 98 feet, and an EF-240 on a 10-foot mast above the top yagi. We're in a
> pretty benign wind environment.
>
> Now here's the complex part. I want to re-tension the guys, which were
> originally set a number of years ago at 400 lb all around, and I figured
> as long as I am doing this job, I should do it better, if possible.
> Why? Because each guy set is made of different material, and I suspect
> that should/might influence the desired pre-set tension.
>
> The top guys are 6700-lb Phillystran down to about 15 feet above ground,
> and 3/16 EHS below that. I know it's a mismatch, but I got the Philly
> guy sets cheap.
>
> The second set of guys use Joslyn 21-foot fiberglass power-pole
> insulators on the tower end, and 3/16 EHS the rest of the way to the
> ground. These insulators are only a little heavier than EHS of the same
> length, but pretty stiff, as you might expect.
>
> The third set are 3/16 EHS all the way, insulated at the tower.
>
> My question is this - what, if any, adjustment would you make to the
> 400-lb pre-tensioning value for each guy set?
>
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