On 5/9/2011 5:06 PM, Grant Saviers wrote:
> 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.
Phillystran is ...well a bit flexible (no pun intended) and it's light
weight. But that would be like using oversize EHS on the tower. At
least you are not adding the extra weight of 1/4" EHS.
You might want to look up the max rated wind load for basically 100' of
properly guyed 25G.
Second, by using different materials at different levels there is the
possibility of unexpected mechanical resonances. Unlikely, but not an
impossibility.
I would not under any circumstances exceed 10% of the "weakest link's"
(3/16ths EHS in this case) breaking strength with the pretension.
> 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.
I agree the pier pin is a real plus, but I've been on a 100' 45G guyed
with HPTG6500? with a far greater wind load in winds gusting to 30 and
could feel no movement.
http://www.rogerhalstead.com/ham_files/Tower29.htm That's not much fun
even on a solid tower, let along one moving close to 3 feet. I have been
on towers that did move around less than that with very little wind and
it'd definitely noticeable.
73
Roger (K8RI)
> 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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