"Shells of double curvature both the synclastic... and anticlastic... are inherently better suited to resist loads by direct forces than are shells of single curvature. The reason for this is obvious from the fact that this type of shell possesses arch action along both curvatures. But in order that surfaces curved in two directions behave as a shell, it is important that proper support or edge members be provided. The direct stresses throughout the major portion of the shell are usually of little significance except as they relate to . A careful evaluation should be made of the bending moments produced in the vicinity of the edge members by the interaction of the edge member and the shell. For moderate size shells, this effect usually is confined within a few feet of the vicinity of the edge member. ... An exception to this are some anticlastic shells, like the hyperbolic paraboloid, wherein bending can prevail throughout a greater portion of the shell. To a limited extent, this also occurs in s, when the supports do not provide a reaction tangent to the shell surface. In these cases, the bending moments may extend a significant distance into the shell."