An Investigation on the Seismic Stability of Persian Brick Arches

The application of structural arch form in Iran goes back to as far as thousands of years ago. Arch is a fundamental component of Iranian architecture. Other structural systems such as vaults and domes which are used widely in variety of structures are indeed derived from arches. In the present study, the stability of various Iranian arches versus their weight, surcharge and earthquake action is investigated. The selected arches are some of the most applied Iranian arches like: parabolic-shaped arches, onion-shaped arches, four-centered pointed arches, obtuse angel arches and basket-handle arches. The selected arches are modeled in AutoCAD software and then are exported into the ANSYS software for necessary analyses. The static analysis, modal analysis and linear and non-linear dynamic analysis have been carried out on the finite element models of the arches. Comparison of the results of the analyses showed that for the same span and thickness in various Iranian arches analyzed in the present study, the parabolic-shaped arch has a better bearing with respect to gravity and lateral loads. The static stability of the arches under the gravity load increases with rise to span ratio of the arch. The other factor that affects the arch stability is its angle of contact to the baseline. According to the two above mentioned factors the stability of the selected arches increases in the following order: the semi-elliptical arch, the parabolic-shaped arch, basket-handle arch, circular arch and four-centered pointed arch. The eigne-value analyses have shown that the natural period of the arch in sensitive to the form of the crown. For the same span, the arches with tipped crown possess larger periods. In this regard, the fundamental period for parabolic arch is the least. This shows that this type of arch is stiffer that the other ones. For dynamic analysis of the selected arches, three strong ground motions of Kobe of Japan in 1995 (ML=7.2), Tabas of Iran in 1978 (ML=7.8) and Manjil of Iran in 1990 (Mw=7.4) were selected. Again, the time history analysis of the arches shows that the strongest arch against the selected accelerograms is parabolic arch; and the order of relative seismic stability of the arches descending from high to low is as following: the parabolic-shaped arch, the basket handle arch, the four-centered pointed arch, the Semi-elliptical arch and the circular arch. Also, under the Kobe earthquake accelerogram, the parabolic arch showed no collapse. However, the other arches encountered collapse and among the circular arch collapsed at 5.8 seconds as the first arch and the basket handle arch collapsed at 8.5 as the last one. As another result, the location of cracks in the arches damaged by seismic loading was in the internal face of the arch.