The conservation of the built architectural heritage in seismic-prone regions is an increasingly topical task in modern civil engineering. The ongoing diffusion of structural health monitoring systems calls for innovative and efficient methodologies for damage identification and condition assessment from experimental data. For this purpose, the paper proposes a novel model-based approach to relate the variation of the modal properties of the structure to increasing levels of seismic damage, looking into the outcomes of pushover analysis from a frequency-domain perspective. The forward problem is addressed through nonlinear static analyses, in which the structure is progressively damaged by simplified distributions of earthquake-induced horizontal forces, followed by a modal analysis of each degraded damage state. The solution of the inverse problem, starting from experimentally identified variations of the spectral properties and exploiting the simulation results, efficiently provides valuable insights into potential damage levels suffered by the structure. The methodology is exemplified by the application to a continuously monitored monumental masonry palace, the Consoli Palace of Gubbio, Italy, which was recently hit by a low-to-medium intensity earthquake and exhibited a slight reduction of its natural frequencies.

Keywords: equivalent frame model, finite element model, nonlinear static analyses, damage assessment, modal identification, structural health monitoring