Seismic Safety Evaluation of Tabriz Alisha Historical Citadel Using Finite Element and Simplified Kinematic Limit Analyses

Iran with more than 11000 historical & monuments constructions is introduced one of the oldest civilizations in the word. Moreover, most of major earthquake in the world is referred to Iran , that is a serious threat for historical building that because during these constructions usually seismic loads are not considered, therefore it is necessary to identify these buildings behaviour in front of this natural hazard (earthquake), and doing necessary actions to strengthening the buildings and even reconstruct them in some cases. One of these splendid constructions is historical Tabriz citadel or Arge- Alisha Tabriz.
Remained Citadel Alisha is a U shape plan with average 33 meters height, 51.2 meters width, 21.1 meters length. Arge Tabriz is situated in a city that is a high earthquake prone area. Thus because of different faults in this area and Arge- Alisha’s historical & cultural significance, this safety assessment of this building is unavoidable.
Historical masonry structures have complex geometry that because of erosion, humidity and their materials mechanical properties has changed a lot. Usually, there is not enough exact information about compose materials of internal parts of the walls. On the other hand, because these constructions are cultural monuments of a country doing destructive tests for recognizing materials mechanicals properties is against international laws. Therefore producing a numerical model for construction analysis seems difficult, and if applicable solving it by software using FEA programs is time consuming. Simplified Kinematic Limit Analyses (SKLA) is a powerful method for historical building safety assessment analysis and its usage for retrofitting purpose that is permissible by O.P.C.M. 3431 Italian ordinance in both of the linear and nonlinear. In this research linear analysis is used for SKLA analysis. Because of masonry buildings have a rigid box behaviour, often local collapse mechanism (part of structure) is more important than its global collapse mechanism .this method assume that is collapse local, and large part of the structures are collapsed during earthquake. To identify probable collapse mechanism, we can use collapse of similar structure in the past earthquakes events.
In this paper a research has been about this method (SKLA) capabilities for Tabriz Alisha Citadel seismic safety analysis. The results show that it doesn’t have enough safety against earthquake prone loads in the site. The analysis of both methods is more or less similar. Non linear time history response analysis results includes: displacement, stresses, wall’s collapse time, while SKLA only used for seismic safety assessment in different mechanisms. This method advantages such as, no need to exact information about materials mechanical properties and any destructive and non destructive test cause this method to be a powerful tool for evaluating seismic safety of historical buildings especially for huge and complex geometry structures. If we choose behaviour factor of structure 2 based on Italian ordinance, 3 mechanisms will not be active, although capacity and demand of the structure in three mechanisms have close value that indicates getting close to mechanism formation threshold.