Effectiveness of an internal seismic retrofit strategy addressed to Lisbon pre-code masonry buildings

The Metropolitan Area of Lisbon is one of the regions with the highest exposure and seismic risk within Portugal and Europe, particularly due to a vulnerable building stock constructed prior to the introduction of any seismic regulations. The recent seismic shocks recorded in 2024 and 2025 have heightened scientific and public concern about severe forthcoming seismic damage and casualties, underscoring the urgent need for tailored mitigation strategies. In this framework, an internal seismic retrofit strategy tailored to Portuguese masonry typologies is presented in this paper and its effectiveness evaluated. Given the limited availability of empirical data on earthquake-induced damage to masonry buildings, detailed numerical models were employed to better understand structural seismic responses and to predict likely damage scenarios. Simulations were conducted using the Applied Element Method coupled with Incremental Ground Acceleration analysis, enabling detailed structural modeling with relatively low computational demands. This study provides an updated seismic fragility assessment of pre-code masonry buildings in the Metropolitan Area of Lisbon and evaluates the effectiveness of the strengthening strategy by calculating the damage probability reduction with respect to the bare configuration of the models. The results provide critical insights to inform risk assessments and contribute to the development of targeted retrofit measures, aligned with code seismic hazard and compliant with heritage preservation regulations.