corrugated steel farm silo

huangyhg

corrugated steel farm silo
i have a 17 foot diameter corrugated steel (probably 20 gauge material - individual sheets are 3 feet wide by 12 feet long and are bolted together (approximate spacing of bolts is 2 inches))silo approximately 30 feet high.  the silo was used to store cattle feed but i would like to add a 12 foot wide by 10 foot high door opening and use the silo to store a farm tractor.  i would like some thoughts as to how i need to frame around the opening and a suggested lintel to maintain the structural integrity of the silo.
the best would be to add complete 3d lattice framing in h setup, where your doors are under the dividing horizontal line in the h, and add atop your silo a polygonal lattice horizontal framing to take the top points of the h framing, this to involve the whole silo strength. this may require other additional vertical   
frankkaw,
as a silo the cylindrical shell was subject to horizontal internal pressures, vertical loads due to the weight of the feed, and the overturning loads due to wind or seismic.
as a tractor shelter, it still will be subject to the same wind loads, and to reduced weight and seismic loads.
as a cylindrical shell it was a very efficient shape to resist those loads.   but a 12-foot door opening will reduce considerably the strength of the shell.   
i agree with ishvaaag's idea to provide a tridimensional framing composed of two straight walls approximately 2.5 feet long by 10 feet high, projecting out of the cylinder, and joined at the top by beams supporting the shell above the opening.  each wall could consist of two columns joined with a vertical lacing. one column to be connected to the shell, and the other would form the jamb of the door.
the top element could be two beams 12 feet long, spaced 2.5 feet, with short beams between them supporting the shell above the opening, and lacing for lateral stability.

siding on the walls and two meniscus-shaped roof decks would provide weather protection if desired.
all the structural members have to be sized for the applicable  gravity and wind (or seismic) loads.
good luck!