My hangar is actually based on a tube structure similar to what you're
contemplating. I was constrained to the same style and manufacturer as the
ultralight guys who started the row of hangars I'm in, or else I would have
built a regular pole building with wood trusses and steel siding and roof.
Alternatively, the Cover-It frames are far superior, each one being a truss.
I almost got them to agree to my using one of those...
But, since I had to conform to what they used, here's what I built. It's
narrower than what you want at 38', but it's free span. With center poles
you could go lighter or wider no problem, but that sort of defeats aircraft
use. The length is essentially unlimited but in my case I was constrained
to 25 feet because it had to match the others. The hoops are 2" galvanized
tubing (don't remember the gauge - guessing 18 ?? It's standard fence
tubing). I trussed every other hoop with a simple tube running across about
4' below the top of the arch and braced with a vee of tubing up to the
center of the hoop. A couple of diagonal braces from each corner of the
wall up to the upper structure add some wind bracing to the top. 8' walls,
2x4 purlins, steel barn siding on the sides, and a tarp top. It's all on a
pad of grade 8 rock (a mix of crushed stone up to fist size, and
screenings). The hoops are set into tubing sockets in 4' of concrete (dug,
set, and poured before erecting the hoops). The floor started out as the
heaviest (silver) grade of tarp HF sells -- 2 years later I poured a
concrete floor and left the tarp as a heavy-duty vapor barrier. Lots
stronger than heavy Visqueen. I also built stud wall sections faced with
1/4" plywood to slip between the trusses. The walls wind-brace the hoops
and make a surface to hang cabinets, etc. without putting their weight on
the structure itself.
It's held a couple of feet of snow, but I usually get out there to clear it
when there's a significant snow that doesn't just blow and slide off. The
white tarp top does make for great lighting inside on even a dark day.
Moisture is just not a factor, I presume because of the vapor barrier. It's
in a grassy area that tends to get some standing water, but my floor is high
enough to stay dry, and I did run the vapor barrier up the sides of the
structure, which formed the sides of the salb when we poured it.
Karl
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