[TowerTalk] guy posts math

[Jim Lux]

On 7/16/15 12:41 PM, Bill via TowerTalk wrote:
> Suggest you contact an engineer.  Wood is a far different  material than
> whatever you are using.  Variables include:  diameter of  the pipe, thickness
> of the wall, whether the interior is filled with concrete  and rebar.
> Anything you might come up on your own is an educated guess at  best .  I'm not a
> big fan of guessing on a 100 ft tower.
>

Look in the list archives (or google) for "elevated guy"..

Basically, it all depends on the angles.

lateral force on guy post = tension of guy*cos(angle of guy with ground).
The tension is the static tension plus any load from the wind.

Force tending to pull the post out of the ground = tension of guy * 
sin(angle of guy with ground).

Bending force on post is Length of post above ground * lateral force on 
post.


Backstay forces work the same way..

The lateral force is backstay tension * cos(angle of backstay with ground)

Force pulling top of post down = backstay tension*sin(angle of backstay).

If the post is set up so that it doesn't bend, then the horizontal force 
from the guy has to equal the horizontal force of the backstay.

Most people have a very steep backstay (otherwise, you'd just anchor the 
guy farther out).  That leads to pretty high tension in the backstay: 
for instance, if your post is 8 ft high, and you've set the backstay 2 
feet out, the angle is 86 degrees.  If you need to resist, say, 1000 lbs 
horizontal force, then the backstay tension is 14,000 lbs..