The Process of Changes in the Appearance and Structural Elements of Bulbous Domes During the Timurid and Safavid Period in Central Asia and Iran

Bulbous domes are among discontinuous double-shell domes and were built in Iran in the early nineth century A.H. Previous domes were shaped pointed and there was no bulge coming out beyond their base diameters. But in the Timurid period, dome profile was changed so that it began a return below the base of the arch, producing thereby a slight bulge. The main question is that what are the reasons for the changes in the appearance and structural elements between two shells after the initial formation of these domes in Central Asia and then their evolution in Iran. This research is written with the aim of finding the hidden aspects in the development of bulbous domes based on both historical documents, and architectural remains, and also examines the reasons of the changes created in these kinds of domes during four centuries in the context of cultural Iran. This study has a descriptive-analytical approach for exploring case studies, which are selected based on primary and secondary sources and also field research. The appearance changes of bulbous domes include removing flutes from the outer shell, adjusting the height of the drum and creating more bulge at the place where the outer shell joins the drum. In this article, the structural changes to improve the strength of the domes, the change in the number and proportions of the stiffeners to prevent the damage of the dome, as well as the shape and arrangement of the wooden struts to increase domes flexibility against seismic shocks, have been examined.