THE GROINED VAULT
A vault can be constructed from parts of four trumpet shells, as shown in the sketch. It may be built without ribs because the curvature of the edges makes the shell sufficiently stiffer and the intersection of the surfaces creates two rigid crossed arches which carry the loads to the supports. Again, this structure is formed with straight lines even though there is considerable curvature to the final surface.
A very dramatic effect can be obtained by continuing the shell beyond the edges shown in the sketch.