So basically a 3' wall with 1 1/4 PVC as the hoop roof. My concern is a buddy who is helping me build this is strongly recommending the PVC be filled with concrete. A little background: I live in Prince Edward Island, Canada. We get upwards of 100 inches of snow a year, and winds that can gust to 60mph. Even summer is breezy, since we are an island. Is the concrete overkill?, will it make it more wobbly?, or is sand good to use for fill, or no fill at all. I am using 6mil UV greenhouse poly as the cover and sides...
definetly not no fill, i wanted to do sand but i had no means of injecting it with confidence. Are you planing on injecting the concrete after its erected? cuzz thats a pretty small hole practicaly a mortar mix. If you did it on an open end I dont know how your going to bend it wet and it wont bend dry. Id bend one and let it dry in the sun or do it now if you still have frost, either test will expose issues of expansion and contraction that may burst the pipe. Everything ive build of pvc has fractured over time or warped under load only to harden warped and then fracture under the next load. Im sick of using it and now only do my structures out of that galvanized canopy pole metal, way more expensive but she does budge in wind or snow. I've seen so many smashed greenhouses of pvc that I really hope cement is a solution for you and for the many more people to come.
We built one of these about 18 years ago. We used the rebar inside of the PVC,, it makes a big difference on the stability .Not sure about your location and climate but you should know that the PVC breaks down after a few years.Ours lasted about 10 years before it "blew up" as in a wind storm came through and the PVC had deteriorated to the point it popped the hole thing leaving only a couple of pieces intact the rebar, the wooden frame and the planter benches.Not cool..
If you want a hoop, have seen galvanized metal fence pipe bent that way and works well.
Seen photos of welded wire concrete reinforcement (same that is used for diy tomato cages) as the supporting arch.