Amplitude Dependency Effects in the Structural Identification of Historic Masonry Buildings

Masonry buildings form a significant part of the central-European building stock. Despite significant efforts to standardize the seismic evaluation of such buildings, uncertainties pertaining to material properties and modeling assumptions introduce significant ambiguity. Operational modal analysis tools have been exploited to infer global structural stiffness properties, under the assumption of linear elastic behavior. However, measurements on real structures demonstrate nonlinear structural responses in the range of small strains, typically attributed to material cracking or to the soil. This work reports analysis of dynamic measurements on three real buildings at various amplitude levels, due to vibrations that are arbitrarily induced by construction works preceding planned demolition. The results show transient frequency drops that are attributed to increasing excitation amplitude, while the response remains in the commonly assumed linear elastic regime. This amplitude dependency remains poorly investigated, as vibrational data of higher amplitude for real masonry buildings are scarce. The evaluation of the impact of amplitude dependency on the, commonly assumed, linear elastic stiffness properties bears notable impact both in terms of model updating, as well as in terms of data-driven damage detection after disastrous events.