Efficiency investigation of structural interventions based on in situ ambient vibration measurements on Acheiropoietos Early Byzantine basilica, Thessaloniki, Greece

Abstract

Acheiropoietos in its current state is a typical Early Byzantine three-aisled timber-roofed basilica with narthex and galleries. During the destructive earthquake of June 20, 1978, the basilica suffered significant damage. In the following years, ambient vibration measurements were performed at the damaged structure before any intervention and main eigenperiods of vibration were calculated. In 1990s, an extensive structural restoration project was undertaken aiming at the provision of diaphragms of controlled shear strength and rigidity at the level of the timber floors and roofs of the galleries. Horizontal steel frames were placed at the perimeter of these diaphragms providing the required diaphragmatic response. The interventions were intended to support the long north and south walls and galleries of the basilica by its stiffer east and west walls against horizontal actions. Within the framework of the present study, the efficiency of the interventions to achieve the desired diaphragmatic response was investigated by measuring the structure’s response to ambient vibration. The in situ measurements and the postprocessing data document that the timber diaphragms are actually behaving as rigid levels. Therefore, it is concluded that the implemented interventions on the basilika assure its proper diaphragmatic function, improving thus successfully its dynamic behavior in future earthquake excitations, according to the redesigned structural approach.