Revisiting khashkhāshi’s definition and structural role in the design of detached double-shell pyramidal and cone-shaped domes, historical city of Kashan

Stiffeners, called khashkhashi in Farsi, are one of the structural elements in double-shell domes built in the space between two shells. Previous studies have mostly examined this element in onion-shaped double-shell domes. However, pyramidal or cone-shaped ones, called rok domes in Farsi, have been largely neglected to date. Therefore, this article aims to 1) provide a comprehensive and grounded definition of stiffeners in detached double-shell rok domes by surveying their morphology 2) identify the structural role of stiffeners in this kind of domes. To this aim, the historical city of Kashan is chosen because of the significance of the number and diversity of cases. Followingly, ten cases are examined outside and inside the city’s historical walls. In the first stage, six examples which have been documented in monograph research; have the possibility of direct field observation; and include various combinations and designs of khashkhāshi; are selected. In the next step, the data regarding architectural designs and structural characteristics of khashkhāshi in the selected cases are collected through “direct observation and field survey” and “supplementary library and archival studies.” To compare the structure of stiffeners, the third stage is dedicated to presenting a three-dimensional model of the cases’ structure applying novel architectural drawings. Finally, through the application of the descriptive-analytical method, the design of khashkhāshi is compared in number, position, dimensions, shape, and construction technique. This path provides a new definition for the khashkhāshi in double-shell rok domes through introducing three distinct structural forms assigned with different structural roles. Overall, when compared to onion-shaped double-shell domes, in rok domes, khashkhāshi plays a predominant role as a stiffener for the dome's neck and the outer shell, rather than serving as a buttress. The results obtained are only applicable for gaining a general understanding of the structural behavior of khashkhāshi in rok double-shell domes and cannot be directly used for the analysis of the specific cases.