Iran, due to its geographical location in the Alpide belt and the presence of numerous active faults, is considered one of the most seismically active countries in the world. This situation places the nation's valuable historical buildings at serious risk of earthquakes, making their preservation a vital concern. Many of these structures, including the Tomb of Bashir and Nazir in Behbahan County, dating back to the Safavid era, were constructed using traditional materials. These materials have a high vulnerability to seismic loads due to their low tensile and compressive strength, high weight, high stiffness, and insufficient ductility. Weak structural connections and the absence of tie beams under the walls also exacerbate the vulnerability of these structures to earthquakes.
The Tomb of Bashir and Nazir, with its Safavid-era antiquity, is one of Behbahan's historical buildings that requires urgent and scientific restoration interventions due to dilapidation, structural cracks, and damage caused by atmospheric and human factors. This structure, built with stone and gypsum mortar, holds special significance from the perspective of Islamic architecture and art history. This research aimed to assess the seismic vulnerability of this tomb, employing qualitative approaches to analyze the structural condition. This assessment was based on geological and seismological studies of the Behbahan region, analysis of the building's structure and materials, and the use of a qualitative assessment checklist.
Qualitative assessments revealed that despite possessing reinforcing elements like buttresses, the building performs poorly under seismic loads due to non-resistant materials, weak structural connections, absence of horizontal and vertical tie beams, structural cracks in walls and ceilings, and inadequate ceiling-to-wall connections. Observations of deteriorated gypsum layers and structural cracks, as well as an examination of the inscription on the portal, are examples of the qualitative assessments conducted. Deficiencies in the drainage system and gradual material degradation also contribute to this vulnerability. The load-bearing walls of the building show poor seismic performance due to a lack of integrity and insufficient connection to each other and to the roof. The heavy weight of the roofs and the lack of sufficient bearing length for them could lead to the sliding and collapse of the walls.
The soil conditions of the region indicate that the tomb is located on soil types 2 and 3. Dynamic structural analyses also confirm its vulnerability to the region's seismic accelerations. The seismic assessment of the Behbahan region, based on Standard 2800 and Topic 6 of the National Building Regulations, classifies this city as an area with high relative risk. Behbahan's high seismic potential is influenced by the activity of faults such as Izeh, Aghajari, and Behbahan, which can generate significant ground acceleration. The nearest active fault to the Tomb of Bashir and Nazir is located only 10.5 kilometers away. The qualitative vulnerability assessment also indicates that the use of traditional materials like stone and gypsum mortar, the high weight of the slabs, and moisture penetration into the materials are major factors increasing seismic risk. These structures lack sufficient ductility and, due to their stiffness and high weight, show a strong response to earthquake waves.
Finally, strategies have been proposed for the seismic retrofitting and preservation of this valuable historical building. These solutions include strengthening the walls, improving connections, lightening the roofs, and using structural tie-beaming. These measures can significantly aid in the sustainable preservation of the Tomb of Bashir and Nazir against potential earthquakes and safeguard this historical heritage for future generations. Seismic retrofitting and strengthening of historical buildings are considered the most logical and correct approach to protect them against natural hazards, especially earthquakes.