[TowerTalk] Fwd: Fwd: Tower foundation and bedrock

[Grant Saviers]

In addition to Steve's cautions, I would add that crank ups depend on 
the hoist cable strength to stay elevated (unless a locking tower which 
is designed to be guyed when locked).  Guys add a lot of downforce on 
the hoist cable, both from the preload, and then several times more at 
max wind velocity.  So check out the design calcs for all cable loads 
against its rated break strength.  Sheave and winch winding diameters 
also affect the break strength as do the sheave axles.

All together, the PE calcs I have would strongly advise against adding 
guys to my HDX589.  If the analysis shows the bottom section or anchor 
system is most likely to fail first, then I don't think there is much 
downside to adding guys to it, since the ground level wind field 
probably won't add a lot of tension to those guys.

Grant KZ1W

On 4/11/2019 8:45 AM, k7lxc--- via TowerTalk wrote:
>>    I made a lot of simulations for various wind conditions and found out that my tower, unguyed, was going to safe sustain wind up to 85 mph with a surface area of 20 sqft. As the wind, frequently, reaches that value where I live, on a hilltop in Southern Vermont, I simulated the possibility of adding guy wires. That increased the safe sustained value to 135 mph. So, against all advice, I have a guyed tower that can be unguyed.
> 
>      I don't have a problem with guying a self-supporting tower IF the guys have very little tension on them (less than 40 or so pounds). Tower strength comes from the legs - the more tension you put on the guy wires, the more compression you put on the legs thus decreasing the capacity of the legs to support the tower. With a small amount of tension, you're not trying to hold up the tower - just restrain it from wind forces. With little or no tension, you could be subject to wind slamming - a violent and potentially fatal condition.
> 
>      What is a guyed tower that can be unguyed per your comments above? I'm not sure what that means.
> 
>>    I don't know where this misnomer comes from that a self-supported should be weaker if you added guy wires. Maybe somebody can tell me. I understand if the guy wires have a very steep angle the load on the tower will increase but that is not the case with mine.
>      It's not weaker - it just has potentially less capacity.
> 
> Cheers,Steve     K7LXCTOWER TECH -Professional tower services for amateur and commercial
> 
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