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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