THE LAZY S
The name applied to this shell is derived from the resemblance of the shape to the term for a cattle brand, called Lazy S. The clerestory provides for natural light and the effect is similar to the Z shape described in the chapter on folded plates. The combination of concave and convex shapes increases the effective depth over the depth furnished by a single barrel. The edges are unstiffened but if they have considerable curvature, the stresses can be satisfactory. However, spans should be kept fairly short to reduce both deflections and stresses.
The design of graceful stiffening members to support these shells is difficult because the shell does not conform to the shape of either a beam or an arch and is unfamiliar to the eye. However, since there is plenty of light coming form the clerestory, the stiffeners can be made like walls and the windows may be omitted.