BASIC ELEMENTS OF SHORT SHELLS
This sketch illustrates some of the principle parts of a short shell structure: 1) the shell spanning between arches, and 2) the arch structure. In this structure, the edge beams are provided at the lowest point of the shell and the arch is placed on top of the shell so that forms may be moved through the barrel. In small structures, the edge beam can be omitted if the shell is thickened. The curve of the shell is determined by the proper shape of the arch and may be a circle for small structures or may conform to the thrust line of the arch for long span structures.
The minimum shell thickness should be at the top in the center of the span. At the arch, the shell thickness is increased slightly for local stresses. The thickness increases toward the springing line of the arch and if not supported by an edge beam, the thickness here should be based on the thickness for a slab spanning the same distance. The edge beams act like the folded plate structures described in the first chapter.