Seismic interferometry for earthquake-induced damage identification in historic masonry towers

Abstract

The inherent vulnerability of masonry structures to seismic events makes Structural Health Monitoring of pivotal importance for the conservation of architectural heritage. In this regard, methods based on Operational Modal Analysis are becoming popular for damage identification. Nonetheless, these techniques may fail at detecting local damages with limited effects on the modal properties of the system. Recent studies report seismic interferometry to be a promising alternative for seismic damage identification of structures. This technique assesses the travelling times of propagating seismic waves between pairs of sensors, which are directly related to the local stiffness of the structure. Therefore, damage-induced degradation can be tracked through wave time delays. While some encouraging results have been reported on the application of acceleration-based seismic interferometry to reinforced-concrete structures, the number of works on masonry structures is far scarce. In this light, this paper is aimed at investigating the suitability of acceleration- and strain-based seismic interferometry for damage identification in historic masonry towers. To do so, an analytical layered Timoshenko beam model is devised for the wave propagation analysis of masonry towers under base motion. Parameter sensitivity analyses are first reported, with a special focus on the effects of dispersion upon system identification results. Secondly, a validation case study of a 41.6 m high masonry tower is presented. A realistic three-dimensional non-linear finite element model is built and subjected to seismic inputs causing increasing damage severities. The numerical results, used as pseudo-experimental data, demonstrate that it is possible to identify (detect, localize and quantify) earthquake-induced damages by wave propagation analysis of strain/acceleration records and inverse calibration of the proposed Timoshenko beam model. A particularly notable result is the possibility of detecting, localizing and, to some extent, quantifying earthquake-induced damage in a fully data-driven way by simply measuring wave travel times between pairs of sensors.