[TowerTalk] Tower Guy Calculations

[jimlux]

On 10/13/19 10:46 PM, Grant Saviers wrote:
> What really goes on in a guyed tower is pretty complex.  A simple static 
> analysis might be possible with a spreadsheet, but not a realistic 
> analysis IMO.

One could probably get within 10% for a simple system, where you assume 
a single guy, rigid (not flexible) bodies, equivalent flat plate areas 
for the tower, and antenna.  That's basically trig, with the complexity 
of 3 guys (as the wind blows from the direction of a guy, the tension 
increases on one and decreases on two)




Where it starts to get real tricky is when you have multiple guys 
attached at different heights.  And you're not going to get is a good 
model of the flexing of the tower, the loads on the tower structural 
members, etc.  AND it's going depend a lot of some good quality 
estimates by the ham of drag areas.

That might meet the OP's original request of "Does anybody know of a 
tool for calculating the forces associated with sizing guy wires on a 
tower?"


> 
> Kurt K7NV a long time ago did a Finite Element Analysis of a simplified 
> tower structure using the standard Rohn section properties.  His model 
> is not a detailed model of the actual lattice construction, hence 
> failure modes are coarse approximations.  His website has that analysis 
> last time I looked and it is quite instructive as to how a guyed tower 
> behaves.  k7nv.com

http://k7nv.com/notebook/towerstudy/towerstudy1.html


> 
> Recall tower axiom #1: Follow the tower manufacturer's design unless a 
> PE provides an analysis.  If what is wanted is different than the 
> catalog designs, then it is time to hire a PE. Many configurations are 
> possible that are not in the catalogs.


> 
> Unfortunately, two PE's I have used are refusing amateur radio tower 
> analysis jobs because too many hams don't implement to the plan, or 
> don't want to pay the fee, or want to argue with the numbers. The 
> hassle, cost of the required software, and liability risk aren't worth it.

Interesting, but not surprising.

The PE has to worry about defending the lawsuit, even if the ham didn't 
follow the plans, but used them to get the building permit, and then 
later overloaded the tower.  Your wet stamp is on the plans and that's 
the *first* place they'll come to when something bad happens.



> 
> Grant KZ1W
> 
> On 10/13/2019 7:51 AM, Tom Hellem wrote:
>> Does anybody know of a tool for calculating the forces associated with
>> sizing guy wires on a tower? It feels to me that this would lend itself
>> rather easily to a spreadsheet where one could enter the variables of his
>> installation and the spreadsheet would spit out the results.
>> I found a few rudimentary calculators on line but they don't seem to 
>> quite
>> take it all the way.
>>
>> Any engineers out there willing to share something like this? I think it
>> would be very useful to anybody who has or is contemplating the
>> construction of a guyed tower. I personally know of a few installations
>> that look like a catastrophe waiting to happen and not being an 
>> engineer or
>> tower erector I am having a tough time convincing the owners of these
>> installations that they should make some improvements.
>>