Damage and performance evaluation of masonry churches in 2009 L'Aquila earthquake

The seismic behaviour of masonry churches damaged during the 2009 L’Aquila earthquake is studied in this paper. Four important basilicas are considered in order to derive general conclusions from the damage assessment and the performance analysis. As a general result of the comparison between the post-earthquake survey activity and the structural analyses the possibility of evaluating the seismic safety of churches, and therefore of avoiding destructive damage by means of the design and application of appropriate retrofit interventions, is confirmed. Comparative numerical analyses on a sample of four churches have highlighted another important aspect: the dynamic excitation due to the seismic ground motion activates many vibration modes of the building structure, though all of them are characterised by small participation factors. This fact leads to the following important consequences: the high spectral values of the registered record of the L’Aquila earthquake do not correspond to equivalent high values of base shear; in particular the results showed that in all the examined case studies, the base shear V ratio ranged between 20% and 30% of the church weight. Therefore the appropriate choice of the force reduction factor to be adopted for these monumental buildings is not so large since the real shear force value was significantly smaller than the plateau value of the spectral acceleration provided by Italian Code. Furthermore, the awareness of the activation of many local modes under seismic excitation calls for retrofit interventions which have to ‘‘tie up’’ the building, thus avoiding local failures that are often observed. The final conclusion is that the observation of damage and failures under real experimental actions, like real earthquakes, are a precious means for the advancement of knowledge in the field of seismic engineering.