عنوان مقاله [English]
Iran is located on Alpine-himalayan earthquake belt. Every few years destructive earthquakes happen in Various region of Iran which causes significant amount of material and human losses. Therefore seismic strengthening of buildings especially historical and old religious building, because of their cultural, historical, heritage and touristic values are of great national importance. The objective of this paper is to study the seismic behavior of a special method of retrofit of Urchin domes. This type of semi-conical masonry dome which are found in southern regions of Iran has not been structurally investigated before. As a model for this study the damaged Urchin dome of Imamzade Jafar shrine in Borujird under 2006 A.D (1385 A.H) Silakhor-Lorestan earthquake was investigated. The strengthening method used is by applying a layer of reinforced concrete (Shot-Crete) to the interior surface of the Urchin dome which was evaluated in this study. After sufficient field studies and measurement, the composite structure of the: Urchin dome, lower double layer spherical dome and the masonry supporting walls and pears were modeled using ABAQUS FEM software. The models were analysed and their frequency and dynamic behavior using time-history analysis (THA) were obtained and compared before and after the application of strengthening Shot-Crete layer. Finally by evaluating the results obtained from these studies, the causes of the failure of the tip of this dome was found to be the excessive acceleration at the tip of the dome and weakness and brittleness of the masonry material due to shearing forces. After strengthening the interior of the dome by a Shot-Crete layer the weakness and vulnerability of the dome under the applied earthquake will be significantly reduced.