Keywords: ambient vibration tests, cultural heritage, finite element numerical models of churches.

The earthquake that took place on the 6th July 2009 in the district of L'Aquila concentrated the interest of both technicians and researchers on the structural assessment of existing masonry buildings belonging to the historical centres of Abruzzi, with particular regard to the vulnerability of the many churches dating back to the 16th century. Some religious structures, indeed, have been heavily damaged during the seismic event: they demonstrate the structural deficiencies that caused the loss of valuable architectural assets or entire monumental buildings of great historical value.

St. Gemma's church is certainly the most important religious building in Goriano Sicoli, a small village of inner Abruzzo. In the aftermath of the earthquake the church condition was of incipient collapse, arising from the instability of the facade that represents the most vulnerable part of the church. In addition, the poor quality of the masonry, the scarce constructive techniques and the complete lack of anti-seismic measures have resulted in several local collapse mechanisms.

The current paper presents part of an ongoing study regarding the seismic behaviour of the damaged structure. For this purpose a finite element numerical model is presented. Its geometry has been exactly reproduced by means of a dedicated drawing software, focusing the attention on the details of the arches, elliptical vaults of the aisles and central nave half-moon barrel vault, the supports of the dome and the drum and in addition the reinforced concrete belt courses. The model is then meshed and imported into the non linear software ABAQUS. Subsequently, it has been calibrated considering the mechanical properties provided by codes which have been properly reduced by a damage index are able to interpret well the current state of damage characterizing the features of the church. Finally, an eigenvalue analysis has been implemented in order to prove the reliability of the adopted model by comparing the numerical results obtained with the ones obtained by previously implemented ambient vibration tests in terms of natural frequencies and vibration mode shapes.

Based on the good agreement between experimental and numerical results, the proposed model appears to be suitable for future implementations that should address proposals for both proper intervention techniques and adequate seismic protection systems to be applied.

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