Geometry-based modeling for characterizing design and construction of Ourchin domes

Domes constitute a significant part of Iranian traditional architecture. Iranian architects not only created hemisphere shape domes, they also created conical shape domes. Documents about conical shape domes of Iran are scarce; among conical shapes, data about Ourchin domes is particularly limited due to the rarity of remaining monuments. Most of these domes can be found in the south and southwest of Iran, which suffers from severe weather conditions, dust storms, earthquakes, floods, high and dry temperatures, and even war hazard. Therefore, conservation and documentation of these monumental domes are essential and must be done immediately. This research attempts to document the geometry and construction process as well as discussing the typology of Ourchin domes. Any stepped dome in which the layers are self-similar and the whole structure could fit in a cone or a paraboloid is an Ourchin dome. Ourchin dome geometrical design process modeling is a critical task, in order to conserve, protect, and restore these particular domes. Required data to preserve the geometry of Ourchin domes is presented through text and illustrations. This modeling divides Ourchin domes into three distinct types, which are: polygonal, star, and circular shapes. Results indicate that although Ourchin domes have complex 3D geometry, the building process was actually simple and practical. In the design process, four key factors (plan shape, Hanjar shape, number of regular polygon sides, and ratio between Sha'hang and radius of dome base) define elongation of the dome. Due to the fact that the number of layers is theoretically infinite, the construction process proceeded by the designer's preference. Other circumstances, such as material cuts, fragility of smaller brick pieces, and inability of constructing, all had a profound impact on this choice as well.