Ruled

Ruled surfaces are the most found in the contact faces of voussoirs. Given a thrust surface t and the curves of a surface subdivision c, the most straightforward contact surface would be the ruled surface composed of the various lines passing through c normal to t. This strategy is observable in most classic stereotomy examples such as barrel vaults (ruled, planar surfaces), hemispherical vaults (ruled, conical surfaces) or spiral staircases (ruled, helical surfaces). Another strategy to use these kind of surfaces in the form of hyperbolic paraboloids is to create surface through the two normals in the end points of each side of a voussoir cell. On the other end of the simplification spectrum, we may find complex ruled surfaces (such as the ones found in Self supported ) characterized by a large angle between iterations of the moving straight line, or the puzzle fittings in Puzzle Joints which rely in a variation of the generatrix, can lend themselves to useful tasks such as the avoidance of a centering or stronger bonding.