Seismic evaluation and innovative retrofit of a historical building in Tunisia

This paper summarizes work conducted within the framework of a European Commission funded project on the use of appropriate modern seismic protective systems in the conservation of Mediterranean historical buildings in earthquake-prone areas. The case study is the one-and-a-half-century-old Palace of Ksar Said, located near the Capital of Tunisia. At the center of the palace, a collection of portraits and furniture are preserved in a room of great architectural and historical value which is the most precious part of the building to be protected. Ambient vibration tests were conducted to measure the acceleration at selected locations of the building. Output-only modal identification techniques were applied to extract the modal signature of the structure. A finite element model of the palace was elaborated based on the measured characteristics of stone and mortar and updated according to its measured vibratory response. Seismic vulnerability assessment of the building was carried out via three-dimensional time-history dynamic analyses of the structure. Results indicate a high vulnerability that confirms the need for intervention. A retrofit scheme is proposed that consists of a steel frame directly, attached to the portrait room structure with added fluid viscous dampers. Vulnerability assessment of the retrofitted building reveals a substantial improvement especially in the vicinity of the portrait room.