The Basilica of Collemaggio in L’Aquila: seismic assessment analysis

This paper concerns with the seismic assessment of the Basilica of Collemaggio after the earthquake that struck the city of L’Aquila in April 6th, 2009. The earthquake caused the collapse of part of the transept structures and some damages in columns of the church naves and in the apses area. The historical investigation has pointed out that the church, built in the XIII century, has experienced many earthquakes during its life, some of which caused many damages to the masonry structures of the church, especially the ones of the transept zone, proving the high seismic vulnerability of this part of the church. Because of these frequent earthquakes, the building has undergone many changes and renovations in the past centuries. In one of the last interventions, the two main pillars of the transept were rebuilt but, unfortunately, without the required strength; so, during the 2009 earthquake, these large pillars at the end of the nave collapsed, leading to the collapse of the entire roof of the transept whit its central dome and adjacent vaults. In order to better understand the static and dynamic behaviour of the Basilica, a continuous monitoring, several laboratory and in situ tests, a complete laser scanner survey of the Basilica geometry and a relief of all the damages were carried out. The surveys showed an irregular structural system, with a non-uniform distribution of stiffness due to the different masonry characteristics and the particular geometry of the Basilica. All the information obtained from the surveys allowed the implementation of an overall finite element model of the church able to catch the elastic dynamic behaviour of the structure. The model has been used to implement eigenvalue and response spectrum analysis in order to assess the seismic performance of the Basilica. Furthermore, an analytical model and a partial finite element model have been developed in order to implement a non-linear pushover analysis capable to highlight the behaviour of the columns of the nave. These elements are probably the most authentic building’s components and during earthquakes, even if cracks occurred, exhibited good resistance under transversal loads. The performed analyses have allowed the evaluation of the stresses redistribution inside the columns after cracking. The results have been provided in terms of force–displacement curve and stress pattern, allowing the formulation of possible reasons about their seismic response.