[TowerTalk] Triangular Crank-Up Wind Load Model

[Jim Lux]

At 03:02 AM 1/17/2006, Michael Tope wrote:

>----- Original Message -----
>From: "Kinney John-r17512" <J.Kinney at freescale.com>
>To: <towertalk at contesting.com>
>Sent: Monday, January 16, 2006 4:12 PM
>Subject: [TowerTalk] Triangular Crank-Up Wind Load Model
>
>
> >I have a question pertaining to my Hy-Gain HG52SS tower or any other
> > tower of this type for that matter.  The question: Does anyone have a
> > model or has anyone attempted to model the wind loading of this type of
> > tower, at heights less than full extension?



><snip..>
> >
>
>I haven't done this analysis, John, but when I posed a similar
>question to Karl Tashjian at Tashjian Towers (old Tri-ex), he
>told me something surprising. On the Tashjian LM470, the
>wind rating actually drops when the antenna is partially nested
>because of the way the sections have additional bracing in the
>areas where the sections overlap when the tower is fully extended.
>So as you lower the tower the wind rating drops for while as the
>tower is partially retracted and then come back up to a much
>higher value when the tower is fully retracted.

Mike raises some interesting points.. (and ones that would be hard to 
analyze, too)
Also, consider:
1) When the tower is nested, it might have more wind drag per unit length 
than when extended.  The porosity (if that's the right word) is higher when 
extended.  The moment arm is shorter, but the wind drag might actually be 
higher.

2) Following on Mike's comment from Karl T.: It also might depend on how 
you define "failure".  It might have a higher wind rating in terms of 
catastrophic collapse when retracted, but might actually deform and 
jam/bind easier.

Jim