Comments on Jim's comments below
1) Indeed, this square design does have more material (potentially) than a
triangular tower.. but, mass of material isn't everything (otherwise, we'd
make towers out of aluminum or titanium). There are a lot of square trusses
out there (theatrical rigging, for instance).
2) The diagonal type truss bracing is stronger, for a given mass of metal,
than the rectangular ladder type
3) The stiffness and strength of this design probably comes from the
stiffness of the box members connecting the uprights.
4) A big part of any tower cost is the labor to build it. The rectangular
tower, with square/rectangular tubular members, is a LOT easier to
fabricate, especially without lots of jigs. No benders, no mitercuts, no
fishmouthing for round tubing, etc. This design could be made with a
hacksaw and a stick welder.
5) I'll bet this tower is a lot more comfortable to climb than one with
diagonal struts. (Theatrical truss sections often have one side of the four
with straight across rungs for just this reason).
6) Shipping a 40 foot container from Australia to the US isn't all that
expensive (less than $1000, I think), and is fairly insensitive to the
weight of the item being shipped.. Considering that you could get several
of these towers in a container, the impact of shipping costs is fairly small
(especially if you had them fabricated in a country with lower labor costs).
It's an interesting design, at least, and well adapted to self fabrication.
It's very reminiscent of designs from rural extension services for things
like windmill towers and so forth. If you have lots of time, and little
money, you could buy everything you need to build this design (tool wise)
for a few hundred dollars (brand new... less, used). (Welder, chop saw or
power hacksaw, angle grinder)
No real jigs needed, just chalk marks on the floor, probably.
Who knows, maybe you'll see this design at Harbor Freight soon, cranked out
by the thousand in China.
----- Original Message -----
From: "Jim Jarvis" <jimjarvis@comcast.net>
To: "Towertalk" <towertalk@contesting.com>
Sent: Sunday, January 25, 2004 9:01 AM
Subject: [TowerTalk] square towers
>
> I'm no engineer, but it would seem to me that a
> 4 legged tower would have 33% more material than
> a 3 legged tower. I would also think that the
> diagonal bracing seen on Rohn, for example, provides
> greater strength than the rectangular form of the
> 4 legged tower, without diagonal bracing.
>
> Then, there is the factor that these towers are fab'd
> in Australia and shipped here. (IF they're shipped here.)
> The shipping expense is more than just the weight of the
> metal...it's the included volume, which is clearly greater
> in a fab'd tower than in the raw steel components. The delta
> might pay for US assembly, if there were sufficient demand.
>
> I've requested pricing, but my expectation would be that
> this design will prove 30-50% more expensive than a triangular
> design of equivalent specification, delivered US domestic.
>
> OTOH, the lifting fixture is a neat idea...and might be able to
> be incorporated on a triangular tower, to facilitate assembly.
>
> This one is worth keeping an eye on.
>
> Jim, N2EA
>
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