[TowerTalk] Rohn 25/Crankup loading

[Jim Lux]

----- Original Message -----
From: "Pat Barthelow" <aa6eg at hotmail.com>
To: <kr7x at comcast.net>; <mringel at bluecrab.org>; <towertalk at contesting.com>
Sent: Saturday, January 29, 2005 10:13 AM
Subject: [TowerTalk] Rohn 25/Crankup loading


> >From: "Hank Lonberg" kr7x at comcast.net Said:
> >Malcolm:
> >
> >If you notice the sections get larger as you go downward from the top.
The
> >tower sections get stronger and can handle more moment as you go
downward.
> >Just like the moment diagram for a cantilever beam, which they are albeit
> >vertical. The maximum moment is at the bottom and reduces as you go
towards
> >the top. Rohn 25,45,55,65 are constant in section size.
> >
> >Regards
> >Lonberg Design Group, Ltd.
>
> Folks:
> I notice something different also, in how/where the load is carried on
each
> section of a crankup.  Assuming no blocks installed, and the lift cable
> carrying the total load of the elevated tower sections,   the load is not
> carried down the corners of the tower, at least not directly.   It is
> applied at single  point sources in each tower section, namely the cable
> pulley axle bolts, in my tower, located on the side of the tower trellis
> work. The corner joints of the tower 'float'.  That is, there is no direct
> downward transfer of stress though the three corner tubes of the tower.
> Does this single point source of loading change any basic dynamics of load
> transfer down the tower structure?

You bet it would change the dynamics (and statics, too!)...

One interesting aspect is that the bending loads are carried not by the
cables, but by the overlapped segments.
This would be quite the challenge to "rigorously" analyze, since the
connections between segments are somewhat variable. I'll bet the design
process works along the lines of "design so that you've got BIG margins".