Thermographic investigations and dynamic identification tests for non-destructive structural assessment and enhanced FE modelling of a historical iron-strengthened masonry church

The paper deals with the description of detailed non-destructive in-situ tests and the analysis of the dynamic behaviour of the Santa Maria Maddalena church, located on the Ischia isle and partially damaged by the seismic event of August 21st, 2017. This church is a very special type of structure built in 1896 according to a mixed ‘baraccato’ constructive technique, based on tuff masonry walls strengthened by thin iron profiles in the main parts and timber elements in its back part. After the seismic event, a detailed survey of the church was done and passive thermography imaging as well as dynamic tests under operational conditions were carried out afterwards. The paper outlines a methodological approach where data and information collected from in-situ tests and surveys about geometry, masonry texture, crack patterns and vibration properties are collectively analyzed for the non-destructive structural assessment and finite element modelling of the church. The paper first describes how the experimental outcomes allowed to enhance the knowledge about the “baraccato” construction system specific to this church and its dynamic response under operational conditions. Setting of a three-dimensional finite element model of the whole church is described afterwards, considering the experimental results, to have a deeper insight into the dynamic behaviour of the structure under different assumptions, mainly regarding the constraint conditions at the roof levels and the values of Young’s modulus and unit weight of masonry. Specific analyses have been also carried out aimed at quantitative discrimination of the numerical vibration modes as ‘local’ or ‘global’. The obtained results remarked the importance of accurately planning dynamic tests on similar structures characterized by significant complexity in their structural organization to achieve a reliable assessment of their dynamic behaviour.