Discussion of the role of geometry, proportion and construction techniques in the seismic behavior of 16th to 18th century bulbous discontinuous double shell domes in central Iran

Abstract Discontinuous double shell domes (DDDs) are a construction typology commonly used in Iranian architecture. They are very diverse in terms of geometry and construction techniques. The preservation of these domes, which often represent the most vulnerable parts of the buildings, requires adequate structural analysis. However, this is still an insufficiently researched topic. Geometric principles, such as proportion and symmetry, are the most important parameters affecting the structural behavior of these domes. The main goal of the present work is to numerically assess the influence of geometry and construction techniques on the seismic behavior of these domes. With that purpose, the paper presents the results of a detailed numerical study based on finite element modeling and nonlinear static (pushover) analysis. Four real case studies with distinct geometric characteristics, representative examples of historic Iranian architecture from the Safavid era (16th to 18th century), were selected for the numerical study. Results were systematically compared and they show that the proportions of the domes play an important role in the seismic behavior. The ratio between their height and diameter is a parameter that determines the ability of the system to transfer loads and to tolerate displacements, and also affects the failure mechanism. The position and dimensions of stiffeners contribute to ensure the monolithic behavior of the whole system. In the smaller domes, stiffeners control the crack pattern and evolution, but they are not much influential in the load capacity of the system. In larger domes, stiffeners were proven to be essential for the structural behavior under gravitational loads and for the seismic response of the system. The ratio of stiffeners height to the dome-drum system height was found to be typically based on the golden ratio.