Last week, we looked at how someone might try to use the geodesic frame to construct a second floor on a 19.7’ (6 Meter) 3V 5/9 geodesic dome built with 1 ½” PVC struts. We wanted to build it in a way that left the ground floor free of obstructions and supports. It was an impressive looking structure, but really, it’s no good unless it holds some weight, right? There are a couple of ways to test it. First, it can be done in a CAD setting, assigning strength values to the PVC pipe and to the hub connectors, and then letting the program create a stress map showing where the likely points of failure will be and how much weight it will theoretically hold. Sonostar isn’t that sophisticated yet with our program, although some of our readers may have tried our new 3-D dome configurator that uses CAD to create the domes and covers in a way you can visualize them from any angle. Someday, we’ll include the ability to compute load bearing values based on size, configuration and pipe diameter. But we’re not there yet.
The second way to do a load test is to actually put weight on the second floor platforms and gradually increase the weight until the dome collapses. This is great fun, and we actually can’t believe we can get paid to do this. We’ve done load tests on the dome frames without a second floor, and it’s been useful to understand not only how much weight the frame structure can support, but it shows where the failures will occur. You can see some of these tests on our website at: https://www.sonostarhub.com/pages/hub-load-tests
|So with the dome and second floor platforms all constructed, we decided to use 52 lb. boxes of paper as the weight on the platforms. We got a whole pallet of paper (40 boxes), assuming there was no way we would go through it all.|
We decided to load the five platforms from the inside first, with 4 boxes each, making our total starting weight to be 1040 lbs. (20 boxes X 52 lbs each).
Lifting 52 lb boxes overhead is a good workout
Looking in at the first 16 boxes from the outside
Once all 20 boxes were in place, we decided to keep going, since the platforms seemed very strong, even with 208 lbs of extra weight on each platform.
The crew had to stand on stacked pallets to be able to reach the second floor platforms
Loading from the outside, the crew kept adding a box to each platform until we ultimately ran out of boxes. We noticed the struts around the doorway were showing some stress because we had removed 6 support struts to make the doorway. We compensated by only putting 6 boxes on that platform, and 8 or 9 on all the others.
We figured there was no way we would get more than 2000 lbs. on the platforms, so we only had one pallet of 40 cases of paper. When we finally ran out, we had 2080 lbs. on the platforms, not including the plywood.
After 40 cases of paper, 2080 lbs, the dome is showing some strain, but still holding up well.
Video #1 Adding a ton of weight to the second floor of a 6 meter 3V 5/9 Sonostar dome
After we finished, we had planned to take everything down and disassemble the dome. However, we had second thoughts on it and decided to let all the weight sit on it overnight, to see if there was enough strain to cause it to fail over time. In the morning, the dome was still intact, and the boxes hadn’t moved. We left it up another day. Still no failure.
So what’s the conclusion? In this test, a 6 meter (19.7’) 3V 5/9 geodesic dome using Sonostar megahubs and 1 ½” Schedule 40 PVC pipe utilized suspended platforms from the uppermost pentagon and showed they could support well over 2000 lbs, or an average of over 400 lb. per platform. The top center does not collapse, and the sides add extra support to the platform configuration. If someone wants to buy us another pallet of paper, we’ll find out what the absolute limit is, but for now, if you duplicate this experiment, you can be assured that it can handle this amount of weight. Unless you’re hosting the Japanese National Sumo team, you could confidently sleep 5 people up on the second floor of your dome, or store a ton of weight up there.
Video #2 Circumnavigating the dome loaded with a ton of weight
Next week, we’re going to look at some different covers that fit the 11.75’ Bubble Dome. Stay tuned!