Have a pile of 2x4's, and a while before you use them?
Well, if you don't cut them, or use fasteners or glue, they will still be usable in a new project after trying these projects.
The dome was more than 30 feet across. Note that the dome is NOT a geodesic dome, it is actually a lofted tiling. (Which is why it is so flat.)
The bridge supported two adults of my weight, and that of several children, at the same time.
If I were to do this for something permanent, I'd want to bolt the pieces in place at the places that they cross.