Stefania Degli Abbati (a) https://orcid.org/0000-0001-9991-8599
Serena Cattari (a) https://orcid.org/0000-0001-9459-5989
Sergio Lagomarsino (a) https://orcid.org/0000-0002-6597-3474

a University of Genoa, Department of Civil, Chemical and Environmental Engineering (DICCA), Genoa, Italy

ABSTRACT

The seismic assessment of complex unreinforced masonry (URM) buildings is particularly challenging, primarily because of the difficulty in interpreting their seismic response. These structures are often characterized by complex geometries resulting from historical transformations that are stratified over centuries. For this reason, a comprehensive knowledge phase must be combined with the use of reliable numerical models, which are essential tools for identifying the main vulnerabilities, quantifying the expected seismic performance, and defining appropriate intervention strategies, if necessary. The ability to simulate the effects of strengthening techniques on the global seismic response of URM buildings enables practitioners and researchers to design interventions that are both effective and minimally invasive. Within this framework, the paper investigates the potential of nonlinear numerical models and verification procedures to evaluate the effects of strengthening interventions designed to enhance the seismic performance of complex URM buildings, through the case study of the Recanati Town Hall. The building, constructed at the end of the 19th century, is characterized by an irregular C-shaped plan, organized into three storeys plus a mezzanine, and founded at different levels. It was severely damaged during the seismic sequence that struck Central Italy in 2016–2017, which produced a systematic crack pattern in the masonry spandrels, indicating the activation of a global structural response dominated by in-plane behaviour of masonry walls. In addition, the different dynamic response of the main body of the C-shaped plan – taller and founded at a higher level than the lateral branch – led to further cracking at the intersections between the plan branches. An equivalent frame model (EFM) is employed to interpret the seismic response of the Recanati Town Hall and investigate alternative strengthening strategies. First, various modelling strategies are implemented within the EFM to reproduce the building’s complexity, and the numerical model is calibrated against available dynamic identification data. The seismic performance in the as-built state is then quantified through nonlinear static analyses. Finally, the EFM is used to evaluate the effects of different intervention strategies on the structural response, including stiffening horizontal diaphragms, introducing vertical stiffening elements, and hooping techniques.

Keywords: unreinforced masonry buildings; equivalent frame model; nonlinear static analyses; seismic assessment; dynamic identification; strengthening interventions.