Structural Damage Detection on a Single-Opening Masonry Wall Subjected to Differential Foundation Settlements Using Modal Features: Experimental Tests and Numerical Simulations

Operational Modal Analysis (OMA) stands out as a suitable method for assessing the structural integrity of historical masonry constructions, such as towers, churches, and palaces, during their operating conditions. However, it is known that OMA techniques have certain limitations, such as improper detection of localized damage or slight structural defects. To investigate and shed light on these limitations, this study presents an experimental program conducted on a full-scale masonry wall system with a single opening under controlled laboratory conditions. The masonry wall specimen was progressively subjected to damage by imposing differential settlements of increasing magnitude at the foundation level. At each stage, Ambient Vibration Tests (AVTs) were conducted to establish the relationships between modal features and the severity of damage. The outcomes from the experimental program indicate clear variations in the modal features as the level of damage increases. To further substantiate the experimental findings, a Finite Element (FE) model of the specimen was developed, and the experimental results were accurately replicated using non-linear modal analysis based on linear perturbation. The findings from this investigation point out that FE models can be used to replicate the damage-induced changes in modal features of historical masonry constructions, investigating the effect of ageing. Overall, this study provides a valuable demonstration of the use of modal features for the detection of slight-to-moderate damage to masonry buildings. Moreover, analysis results point out that FE models, once properly tuned, can be used for SHM purposes, such as predicting future damage scenarios, as they can faithfully reproduce the decay of modal features.