All:
To give you a different perspective on the amount of overlap
that should be considered in slip joint connections, the
industry recommended practice for tubular and multi faceted
steel transmission and substation structures is 1.5 x the
larger diameter( ASCE Manual No. 72). This assures full
transfer of the bending moment and shear via contact stresses
in the inner and outer faces of the connecting hollow members.
So a good rule of thumb would be 3" for 2" diameter and
smaller and 4 for 4.5 inches for 3" diameter at a minimum.
That being said if you have sucessfully used lesser values and
your verticals have been up for several years, use that
empirical experience to guide you. Sometimes overlaps are
dictated by the minimizing of waste material and number of
cuts based on 6', 12' or 20' lengths of tubing.
As always YMMV and strive to keep em in the air.
Regards
Lonberg Design Group, Ltd.
H.S. Lonberg, P.E.,S.E.
President
Mar 16, 2009 03:28:02 PM, richard@karlquist.com wrote:
> larryjspammenot@teleport.com wrote:
>
> interested in the construction of the 66' DX Engineering
vertical,
> not to use as an actual vertical antenna, but to mount in a
tripod
> on my roof and then use it as a tall support for an 80M
inverted vee.
A data point. I had an inverted vee at 60 feet, using
irrigation
tubing. The bottom 30 ft was 3 inch O.D., and the top 30 ft
was 2 inch
O.D. Wall thickness was 0.050 inch. This is about the
flimsiest
that I would recommend. It wiggled around quite a bit in 70+
MPH winds,
but never fell down. It had 4 way guying at the top and
another
set of guys halfway up. Additional guying wouldn't have hurt.
I am currently using 3 inch for the whole 60 feet. I'm not
worried
about that at all in the wind. OTOH, those tapered verticals I
would
worry about a lot.
Rick N6RK
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