Re-Examination of Various Iranian Domes and Their Divisions Considering Their Shells, Geometric Forms and Components.

Iranian covers have been invented based on the necessities and requirements of their time and have evolved gradually during centuries which has resulted in the creation of different types of them. In general, the covers are divided into two types of flat and curved ones. As a common curved cover in Iran, domes have had great influences not only on the geometric forms of buildings but also on the city perspective. Domes have been used in Iranian architecture more than other elements for their capability of covering a vast area. For the pressure existing among the dome components, any measure including renovation and strengthening must be taken based on the accurate and correct acquaintance with their overall nature and function; therefore, investigating domes and getting familiar with them not only reveals parts of Iranian architecture history but also assists us in proper renovation of these works. Previous researchers have studied and categorized Iranian domes but they have never been categorized extensively according to their shapes, main components and shell numbers. Considering the importance and use of domes in Iranian architecture, this research has been conducted at the aim of reviewing various types of domes and then presenting an extensive categorization based on their geometric forms, components and number of shells. Hence, this is the main question that how many types of Iranian domes there are based on the considered criteria. This research is a practical one and a compound research methodology (historical, descriptive and analytic) has been used to conduct it. The data has been derived from library and field studies (field observations of previous researchers have been used to obtain a comprehensive result.). What distinguishes this research from the previous ones is its variables, the research methodology and samples comprehensiveness. According to the results obtained based on domes shell number, there are 3 main types of dome. Each type in turn includes various sub-categories considering the space between shells, shell form (spherical, conical, combinatorial) and components (beam vault, opium poppy form, fasteners). Single-shell dome has 3 divisions: simple spherical, step-like, beamed domes, conical and domes with cupola. Double-shell domes have 3 main categories which include some sub-categories as well. Integrated spherical dome is the first type of double-shell dome which is the only separated double-shell dome. The second sub-category of double-shell dome is integrated hollow spherical dome which in turn includes simple, box-like, constraint, bladed and beamed forms. The 3th type of double-shell dome is the entirely disunited one which has 3 sub-categories: conical, spherical, combinatorial based on the outer shell form. Spherical dome also has some sub-categories: simple, onion, gothic, beamed, scalloped and zigzag. Double-shell conical dome includes 7 sub-categories: coneshaped, multiply, zigzag, scalloped, step-like, mound dome and combinatorial. For combinatorial dome two types of simple and beamed have been recognized. The last type of dome is 3-shell dome which has two sub-categories of spherical (simple and scalloped) and conical (simple, scalloped and multiply) considering their exterior shells. Totally, 27 types of dome have been recognized and categorized so far. Such form variety is the indicator of not only Iranian creativity but also acquaintance of Iranian master-workmen with the construction techniques and static issues.