[TowerTalk] tower novice seeks advice

[Jim Lux]

At 09:42 AM 5/6/2005, Daniel James Muth wrote:
>Hello all,
>
>As part of my dissertation project I need to erect a 130'
>tower above a lodgepole pine canopy in Montana
>(atmospheric measurements).  The most demanding equipment
>load will be four 120W solar panels that will be powering
>my instrumentation.  The base of the tower will be
>shielded from excessive wind up to about 90' by the forest
>canopy.  Any suggestions as to tower solutions that are
>affordable and up to the task?  The more options the
>merrier.  Thanks,
>
>DM
>
>Daniel Muth
>University of Virginia
>Department of Environmental Sciences
>291 McCormick Rd.
>P.O. Box 400123
>Charlottesville, VA 22904-4123
>(434)924-0594 phone
>(434)982-2137 fax

  Hie thee on over to Thornton Hall and find someone in the Civil 
Engineering department of your college to advise you.  This is, after all, 
what civil engineers do for a living, and realistically, it's a design 
problem that's fairly straightforward, albeit with enough traps and 
complexities that if you have no background, you shouldn't take it on.

How big are your panels? (size and weight) What orientation are they 
mounted in?  Do they need to be at the top, or can they be at "treetop" 
level, and the instrumentation at the top?

What's affordable?

How long does it have to sit there?

What's the regulatory wind and ice requirement for the location?  What's 
the "practical" wind and ice requirement? (The rules may allow you to 
design for 70 mi/hr and no ice, but if you expect it to stand up in 120 
mi/hr gusts with 6" of ice on it, you need to design for that)

What's the impact of failure: i.e. if it blows down, but nobody gets hurt, 
and most of your equipment survives, you can just put it back up; that's 
very different from you've got a million dollar LIDAR mounted at the top 
and there's a preschool at the base.

You've got a few basic strategies, all based on using a guyed tower of some 
sort, which for 130 ft, may be your best bet, cost wise.  If your panels 
are in the 3x5 foot range, you've got a lot of square feet of sail area (60 
square feet).

1) Pick a tower from the catalog that's got more than enough capacity for 
your load (typically figured in terms of weight and "sail" area), and use 
the manufacturer's recommended installation.  This won't allow for any 
increased capacity from the wind shielding, etc., so it's going to be big 
and sturdy.

2) Hire a professional engineer to analyze the situation and formulate a 
recommendation. The engineer will be able to take into account the wind 
shielding, etc.

A lot depends on your regulatory environment.  Most towers that high are 
going to need a fairly good sized chunk of concrete in the ground, which in 
a lot of places would require a building permit.  The regulatory 
environment will determine whether you need a P.E. (licensed in Montana) to 
do the analysis and design.

Jim Lux