Architectural and structural analysis of special karbandis of Tabriz historical bazaar

Covering the roofs of the bazaars due to the diversity of spatial and small and large openings with simple and complex structures. These coatings are available in various bazaar spaces , each with special geometry, both in the final design and in space structures. To cover large openings such as  timche, they used domes and karbandis. Considering the global registration of the traditional bazaar of Tabriz, as well as the great efforts of the architects of the Tabriz bazaar in creating the most beautiful, diversified and most sophisticated types of karbandis in bazaar timches, reveals the importance of studying the Tabriz bazaar karbandis as a sample of this study. Considering the wide openings of the covers in Tabriz bazaar, such as Timche Amir South (14-15 m), the need to use more tiles with high width and height for roof skeletons is created. Therefore, in addition to the boundaries of the field (sideways), other tensions (middle tensions) are formed that appear on the roof. As a result, it separates the features of thiskarbandi  from the usual karbandis. In the study of the karbandis that have been used, the structure of the plan shape affects the form of the design. This means that in a specific context with a certain length-to-width ratio, it is possible to apply certain implementations that affect a variety of factors. These variables are available to the host architect to make decisions about the details of these features. Iranian architects usually try to conceal the elemental elements of the structure behind the cover elements. Such complexity and ambiguity makes it difficult to understand the structure of the karbandis. Existing karbandis on the roof of the Tabriz  bazaar are structurally different from those of the rest. That's why they are called special. In other words, the ribs of the karbandis used in the timche do not follow the usual geometry of the karbandi that is seen from below the ceiling. There are also various karbandis that have the same theoretical geometry, but they are different in practical geometry. Nowadays a lot of Tabriz bazaar vaults collapse and are in an irregular situation that has brought the marketers at serious risk. This erosion situation has been growing and the unconscious disregard for the restoration of karbandis, regardless of their initial structure. Therefore, in the typical karbandis of the Tabriz bazaar, due to the factors mentioned, their structure and shape are not necessarily consistent. The restoration of some of the Tabriz bazaar karbandis has been done without considering this issue and has changed its form. Therefore, in view of the loss of traditional and empirical doctrines on these types of karbandis, disclosure of the desired relationships is necessary. And can be effective in providing their repair solutions and building new ones afterwards.  By recognizing and analyzing the special karbandis of the Tabriz bazaar, we can understand the form and geometry of the form and its implementation. Due to the lack of specialized writing in the field of special karbandis, the contradiction of many of these writings about the performance of ribs in this structure, requires research. In this paper, based on library resources, field studies, and the analysis and interpretation of the findings, a study on the geometry and technology of constructing special karbandis for the cover of the historical bazaar of Tabriz has been completed and the implied concepts have been refereed. For this purpose, by examining the small documentation of the repairs and the implementation steps of the special applications, the geometry of the hidden ribs of this type of karbandis was compared from the roof and its image from inside the space. The result of the study indicates that for the analysis of the special karbandis of the Tabriz bazaar, the characteristics of the structure, structural characteristics, the role of construction and use, the material of the ribs and the structural role should be considered. The geometric form of the karbandis directly affects its size, dimensions, plan, shape.