The dynamic behavior of the Basilica of San Francesco of Assisi

Abstract

During the 1997 Umbria-Marche earthquake, two of the vaults of the Basilica of San Francesco in Assisi collapsed as a result of an 8.5 Mercalli-scale magnitude earthquake. The structure had endured stronger earthquakes for centuries before this earthquake, and there were likely many reasons for the collapse, such as damages accumulated from previous earthquakes. However, one of the factors that may have lead to the collapse is the modifications made to the structure over its lifetime, which could have made the basilica more susceptible to the 1997 earthquake. The basilica's roof has been subjected to three major alterations in its 760 year life. Each alteration changed the weight and stiffness properties of the roof and global dynamic behavior of the basilica. In this thesis, simple analytical models are employed to show trends in the structure's seismic response given the changes in stiffness and mass of the roof over the centuries. The findings of the analytical model suggest that the roof interventions have had the eect of decreasing the structure's fundamental period, and therefore, attracting more seismic forces to existing structural elements. The findings of this study are meant to educate preservation engineers for similar interventions in the future as well as address present day public safety issues regarding retrofitted historic structures. Keywords Basilica of San Francesco of Assisi, Historic Masonry Structures, Monumental Structures, Seismic Vulnerability, Seismic Retrofitting