[TowerTalk] house/foldover

[Jim Lux]

----- Original Message -----
From: "Jim Jarvis" <jimjarvis at comcast.net>
To: <towertalk at contesting.com>
Sent: Wednesday, June 01, 2005 2:49 AM
Subject: [TowerTalk] house/foldover


>
> Bob Gates had an interesting idea, using his new home as a
> guy-anchor for folding over rohn 55g.
>
> A quick stab at the loads:
>
> 120' of tower:  1200lbs spread over 120'...
> we can assume uniformity, and calculate the mass at the
> midpoint moment:  1200 x 60 = 72,000
>
That's 72k pound feet, not 72kpounds, right?


> to which we add antennas, masts, rotor...
>
> yagis @ #95 & 55#, plus rotor @ 12 and
> mast @ ..what...50? = 212 at the top..
>
> 212 x 120 = 25,440
>
> plus yagi @ #95 @ 90... 95 x 90 = 8550
> and yagi @ #55 @ 60'... 55 x 60 = 3300
>
> Then, the weight of the guysets...
> I have no idea how to estimate this, so this is an absolutely
> wrong guess....
> #400 lbs @ 120 = 48,000
> #300 lbs @ 90 = 27,000
> #200 lbs @ 60 = 12,000
> #100 lbs @ 30 = 3,000
>
> (remember, these have to be 4 way guys, or there will be no
> lateral support as the tower comes down....errr, "goes up" might be
> a better choice of words, in this case.)
>
> So...the lateral load imposed on the house/guyanchor, as the
> tower is lowered toward the horizontal is....
>
> 72,000 + 25,440 + 8550 + 3300 + 48,000 + 27,000 + 12,000 + 3,000
>
> which equals....154,290 pounds.

No... I  think that would properly be ft pounds of moment (i.e. length *
force)


If you were pulling it up at a point 20 ft from the base, you'd have "only"
about 8000 lbs of force (at right angles to the tower, when the tower is
laying horizontal).

Then you'd get into the sticky horizontal force component while pulling at
an angle, etc.  If the house were 20 ft tall, and the tower's laying with
the base right at the house, then the cable pulling it up is at a 45 degree
angle, and the cable tension will be 1.414*lifting load or about 11,200 lbs.

>
> (I'll ignore geometry and the varying horizontal component as the
> tower is raised...and just consider how it's going to get up there
> the first time.)
>
> As I said in my initial post....better back-guy the house, the
> trusses aren't designed for lateral load resistance!  Even if I'm
> wrong by a factor of 2 on the dead-weight of the guys, it's still
> over 100k lbs.

The lateral load is probably only a tenth of that, but still a huge number,
and almost certainly, the house isn't designed for a point load of that
magnitude. It might be able to take it distributed over a large area (after
all, the house has to stand up to 70 mi/hr or more winds and earthquakes..
but those are distributed loads. )


>
> This is a 5 am swag, and I haven't had coffee yet, so I may
> have missed something.
>
> n2ea
> jimjarvis at ieee.org
>