victoria's rebar dome - a moringa tree greenhouse (2010)
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(chris vansprouts & victoria white photos, click to zoom)

this geodesic greenhouse frame follows my rebar dome design for ranjit.  it's 22 feet in diameter and about 12 feet tall in the center (slightly oblong).  the great-(semi-)circle arches are made of 1/2-inch rebar about 40 feet long (pairs of 20-foot pieces welded together with a 6-inch overlap).  the ground ring is made with four 20-foot rebars welded into a full great-circle.

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dylan, diana, megan, & chris - raising the arches!  (victoria photos)

all crossover points are measured and marked with the rebar still laying flat on the ground.  at this scale, 1/2-inch rebar is flexible and lightweight enough that just two people, one at each end, can curve and raise an arch by simply walking towards each other.  the arch ends are clamped to their respective positions around the ground ring, and pairs of arches tied together with bailing wire at crossover points by a third person on a ladder.


in preparation for welding, crossing pairs of arches are clamped together with a steel disk between them.  during and after welding, the steel disks are essential to help distribute stress.  (vansprouts photos) 


we have not carefully measured the overall strength of this frame, but it seems sufficient for a lightweight greenhouse.  thicker rebar and/or a denser geometry would probably be needed for a frame to support solid walls and roofing.  more to be learned...

cross-eyed stereo photo of completed rebar frame  (vansprouts photo)

in winter, victoria will cover the dome with greenhouse plastic held down with sandbags to retain heat and protect the tropical moringa trees inside inside from freezing.  in summer, the covering is shade-cloth to allow air flow and prevent overheating in this desert climate.

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summer inside the greenhouse  (victoria photos aug10-oct2, click to zoom)
( further report & more photos in progress... )
also see - rebar dome design - webliography -