Structural Analysis

Using 2×4s Now

Just how strong does the dome need to be? The largest force on the structure comes from the wind, which at Burning Man, depending on who you listen to, gets up to 30 MPH, with 60 to 75 MPH gusts.

So I wrote a C program to simulate the stresses in the members of the dome’s structure from wind. I’ll present the details of the program later on, but here’s the result: in a 60-MPH wind, some members of the dome’s structure experience nearly 400 pounds of compression or tension. (This result is an upper bound because I’ve made some assumptions. Also, the actual values from the simulation are 396 pounds of compression and 362 pounds of tension.)

Another result, which I’ll summarize here and detail later on, is that the maximum allowable stress in the kind of 2×2s that I was planning on using is 285 pounds. Oops. So I’ve changed plans, and now I’m going to build the dome from full, unripped, 2×4s. That doubles the original cost of the wood, but hey, I’d rather have an over-designed dome this year than one that fails.

Source of Joint Plates

As mentioned on earlier pages, I’ve settled on using joint plates to connect the members of the dome. Today I discovered that the “5 plates” are available commercially, and so those will be purchased. See Starplate Building System. Normally these plates are used in “1V” domes, as seen on the web page, but they can be used for the pentagons in a “2V” dome by cutting a narrow wedge from the 2×4s.

I still need to create my own “3 plates”, since I can’t find anyone who offers them.