The diffusion of seismic structural health monitoring systems, evaluating the dynamic response of engineering structures to earthquakes, is growing significantly among strategic buildings. The increasing availability of valuable vibration data is being backed by continuously evolving techniques for analysing and assessing structural health and damage. Within this framework, the paper proposes a novel model-driven vibration-based methodology to support the assessment of the damage level in masonry buildings hit by earthquakes. The leading idea is to exploit, in the pre-event phase, synthetic equivalent-frame modelling and nonlinear dynamic analyses to systematically relate the gradual reduction of natural frequencies to increasing levels of structural damage. The resulting behavioural chart (seismic chart) of the building, constructed by employing computational tools and robustly defined on a statistical base, may provide the theoretical expectation to ascertain a certain level of seismic damage, based on the decrease in vibration frequency experimentally identified in the post-event phase. The methodology is firstly formalized, integrating common identification techniques with a novel damage grade estimation procedure, and finally exemplified for a monitored strategic masonry building damaged by the 2016–2017 Central Italy earthquake sequence. The outcomes of this application confirm the operational validity of the methodology, which can be intended as effective support for the decision-making process regarding structural usability and safety in the post-earthquake scenario.

SummaryVibration tests are encountering a growing success in earthquake engineering as a valuable tool for the seismic assessment of buildings. Ambient vibration measurements, in particular, offer reliable support for the updating of mechanical models, as well as the enhancement of seismic mitigation strategies for existing buildings. In this respect, the common description of the floor diaphragms as planar rigid bodies tends to oversimplify the actual mechanical behaviour of some traditional structural solutions, especially in masonry buildings. This assumption can be violated even in modern concrete and steel buildings due to inadequate design, poor manufacturing, or damage. The paper addresses the mathematical validation of the rigid diaphragm simplification using vibration measurements. To this purpose, a model‐based inverse kinematic problem is stated and solved to discriminate the in‐plane rigid motion and the angular deformation time histories from vibration data. Simple formulas, leveraging the approximate solution in the case of problem under‐determinacy, exploit the spectral content of vibration data to discuss the diaphragm deformability. Natural modes exhibiting different (rigid, quasi‐rigid, or nonrigid) diaphragm behaviour are distinguishable by comparing the power spectral densities of the rigid motion and angular deformation. Modes of pure floor deformability can also be identified. The influence of adverse testing conditions is discussed through pseudo‐experimental data simulating the dynamic response of a simple frame structure. As a complementary contribution, the procedure effectiveness is experimentally verified by analysing vibration data related to, first, laboratory tests on a scaled concrete‐steel frame and, finally, full‐scale tests on a masonry building.

Recent advances in computing performance and simulation tools allow today the development of high-fidelity computational models which accurately reproduce the structural behavor of existing structures. At the same time, advancements in sensing technology and data management enable engineers to remotely observe monitored structures in a continuous and comprehensive way. Merging the two approaches is a challenge recently addressed by the engineering research community, which led to the concept of digital twin (DT)—a simulation model continuously fed by sensor data which, throughout the whole lifespan of the structure, stands as its digital proxy. In the seismic field achieving such a task is still problematic, in particular for large and complex structures such as historical masonry palaces. To this aim, the paper proposes the integrated use of DTs and vibration data to support the seismic structural health monitoring of monumental palaces, discussing a practical application to the historical Consoli Palace in Gubbio, Italy. To overcome the computational limitations of classical approaches, an efficient equivalent frame (EF) model of the palace is built and continuously updated in quasi real-time based on modal information identified from vibration data. The performance and accuracy of the Equivalent Frame model are compared with those of a high-fidelity Finite Element representation, highlighting both their feasibility and limitations. Employing modal data recorded across the 15 May 2021 earthquake, the EF model demonstrates the ability to quickly assess the structural integrity of the palace in the post-earthquake scenario, as well as to forecast the residual capacity with respect to future seismic events.

Post-earthquake damage surveys systematically highlight the seismic vulnerability of monumental structures, calling for simple assessment procedures to address the design of effective retrofitting interventions. The structural complexity characterizing monumental structures, however, makes a reliable prediction of their seismic response a relevant challenge of engineering interest. Ambient vibration tests (AVTs) provide valuable support to achieve such a task, improving the knowledge of the actual dynamic behavior of the structure and, consequently, the reliability of the seismic assessment. In this context, the paper illustrates the integration of AVTs outcomes with the evaluation of the seismic performance of historic masonry structures by presenting the comprehensive application to a case study, the bell tower of the Saint Lawrence’s Cathedral in Genoa, Italy. The research combines the assessment of the global seismic response of the tower, investigated through a simplified mechanical model, with the local verification of the pinnacles placed at its top, referring to a displacement-based approach on a macro-block model. An extensive ambient vibrations measurement campaign carried out in May 2020 allowed for a comprehensive operational identification of the bell tower and its pinnacles, clarifying the ongoing dynamic interaction with the main body of the church. This valuable information was successfully employed, first, to accurately reproduce the actual constraint conditions induced by the church on the bell tower, a determining factor in the modeling of its global seismic response and, second, to reliably quantify the seismic amplification caused by the tower filtering effect to be used as the seismic input for the local verification of the pinnacles.

Historical masonry structures constitute a fundamental part of the built cultural heritage but are characterized by an intrinsic vulnerability to ageing and natural hazards, in particular to earthquakes. The related need to assess their current health condition and to ensure their future conservation is giving rise to increasing efforts in scientific research. The combined employment of health monitoring systems and structural modelling is widely adopted in this field, either to better interpret the effects of age-related degradation or to reliably predict the structural response to earthquakes. Both scenarios can leverage experimental measurements for the model calibration, thus reducing epistemic and aleatory uncertainties in the assessment phase. Among the available modelling strategies, refined Finite Element (FE) models represent the most common choice in the SHM perspective for monumental URM structures. Nonetheless, the computational effort required by the assessments in the nonlinear fieldunavoidable in seismic evaluationsis often unfeasible, especially in practice engineering. In the case of palaces, an alternative is the employment of more computationally efficient formulations such as Equivalent Frame (EF) models. Within this framework, the paper firstly deals with the equivalent-frame modelling and model updating of the Consoli Palace, a historic masonry building in Gubbio (Italy) investigated through ambient vibration tests. The peculiar aspects of the buildinge.g. the unusually high inter-storey height, the presence of vaulted floors, the irregular distribution of the openingsmake the equivalent-frame idealization a challenging task. The comparison with a detailed finite element model developed in previous research points out the differences and limits of the two approaches, providing some suggestions to benefit from their integrated use.