[TowerTalk] Wind loading

[Joe Subich, W4TV]

You're not really concerned about wind load - more about overturning
moment for the base.  You can calculate the overturning force for each
section of the vertical by using length x diameter (both in feet for
square feet) multiplied by the distance of the center of that section
above the base.  Simply sum the forces for each section.

If you are concerned about the bending moment (yield) for each section
you can calculate the bending moment at each joint as the sum of the
forces above that joint and use the standard mast calculations for
that force in the cross sectional area just above each joint.

Instead of wood bases, you may want to look into non-penetrating roof
mounts (the kind that use concrete blocks as ballast).  They are
typically 3' x 3' or 4' x 4' and will hold a considerable number of
blocks if needed to provide enough overturning resistance.

73,

    ... Joe, W4TV


On 8/30/2016 2:20 PM, Gary Smith wrote:
> I'm having to play games with setting up eight, short, active
> vertical elements on an incredibly rocky area. I am not able to drive
> in ground rods, much less the base of the antennas. I'm coming up
> with a plan to make wooden bases for them and hold them down with
> rocks.
>
> Since I live on the ocean's edge and have to contend with hurricane
> force winds every so often, I'm trying to figure out the wind loading
> of the verticals I'm considering. I'll buy the aluminum sections from
> DXE and prefer to use larger sections just because of branches
> falling at the marsh edge, as they always do. But thicker pieces will
> have more wind loading and that is a problem.
>
> If I use the thinnest configuration I'll have about 22 feet tall made
> of .375, .5, .625 & .750 sections.
>
> I asked what the wind loading would be and nobody I talked to was
> able to give me a clue. Does anyone know a formula to figure the wind
> loading of tapered elements?
>
> Thanks & 73,
>
> Gary
> KA1J
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