Performance of a far-field historical church during the 2016-2017 Central Italy earthquakes

Churches are an essential part of the historical and architectural heritage of several countries, and various earthquakes have highlighted the significant seismic vulnerability of ancient religious buildings. On August 24, 2016, a seismic sequence started in Central Italy with a magnitude 6.0 event. Nine events with magnitude ≥ 5.0 occurred between that date and January 18, 2017. Heritage churches were tremendously affected by the sequence, suffering relevant structural and nonstructural damage even far from the epicenters, as in the case of the fourteenth century church of San Francesco in the city of Amandola. The church was inspected several times during the sequence, and a survey was performed using an innovative structure-from-motion digital photogrammetric technique. Ambient vibration tests were carried out on the bell tower before and after the main event of the sequence, and the tower elastic behavior was reproduced by means of a three-dimensional finite-element model. Observed structural performance was interpreted in light of estimated ground motion and literature-obtained models for local mechanisms, with special emphasis on belfry and façade response, and a formula was proposed to account for frictional interlocking between orthogonal walls. Finally, recommendations were developed for troublesome nonstructural deficiencies.