At Sonostar, we’re very pleased with the strength of PVC domes in general, but we know many people are reluctant to take our word it for when we say that these domes can hold a lot of weight. We’ve done quite a few tests on different configurations to try to understand what the failure points are, and we are happy to share the results with you. Besides that, how cool is it to be able to test something until it breaks? That’s what we did in every case, and we continue to do so as we build different configurations.
There are some assumptions we made in the tests that are probably unrealistic. At the outset, we assumed that the weight load could be determined by suspending the weight from particular points in the dome, rather than by loading weight on top of the dome. For someone worried about the weight of snow, for example, that’s probably not valid. Our intuition tells us that weight on top of the dome will spread itself out much more evenly than weight suspended from points under the dome. For that reason, we did two tests: one at the center point in the middle of the dome, and one using the five hubs that are the next extension out from the center hub. We’re assuming both those cases would be the extremes of how weight loads would affect the domes.
As you watch the videos, you’ll see the struts start to deform when they reach their load capacity. In some cases, the deformation gets really out of hand before a failure occurs. In the case of the 2V 15’ dome made with ½” PVC, the dome just kept getting more and more deformed until we finally succeeded in breaking it. We were amazed at how much bend the PVC could take before it collapsed.
You won’t be surprised to find out that 1” PVC is stronger than ½” PVC; and that 1 ½” PVC is the strongest of all. You’re not going to be surprised either that the higher the frequency, the stronger the dome. What may surprise you is how much weight a PVC dome can carry, and the implications that has on cost-efficient construction.
We broke a lot of hubs and quite a few struts in doing these tests, but we figure it’s better we break them than you. Please use good sense when you apply the values you see in these demonstrations. If a 2V 19.7 ’ (6 meter) diameter dome made with 1 ½” PVC fails at 450 lbs., that doesn’t mean you can swing two 200 lb. football players from a point and not expect it to fail. The bouncing and other stresses will cause the junction to fail at a much lower load. We’re not guaranteeing any of these results for your dome, either, because you may use lower grade PVC, you may compromise the holes in the hubs (by drilling through in the wrong places), or any other number of ways that fall outside the testing criteria. We’re hoping these tests will give you confidence that the domes will hold up well with a cover, or some other roofing material, and will continue to function under reasonable loads.