Single or double curvature shells
Single curvature shell : Are curved on one linear axis and are a part of a cylinder or cone in the form of barrel vaults and conoid shells.
Double curvature shell : Are either part of a sphere, or a hyperboloid of revolution.
The termssingle curvature and double curvature do not provide a precisegemoetric distinction between the from of shell because a barrel vault is a dome
The termssingle and double curvature are used to distinguish the comparative rigidity of the two forms and complexity of centring necessary to construct the shell form.