Unreinforced masonry structures are a significant percentage of the global building stock and are often vulnerable to seismic events due to their inherent structural weaknesses and limited deformation capacity. Although seismic codes promote regularity in structural design, achieving this in unreinforced masonry buildings is often a challenging task. Despite extensive research using shake table tests, quasi-static testing of unreinforced masonry buildings remains limited, particularly in the presence of plan irregularity and rigid diaphragm. The present study addresses this research gap by investigating the seismic response of a half-scale, two-story, unreinforced masonry building with plan irregularity through cyclic quasi-static testing. The experimental campaign presented here shows the findings from two tests, including dynamic identification. The first test indicated torsional amplification and rocking-induced wall detachment during the pre-peak response. These results prompted modifications to the experimental setup, including the addition of extra weight to prevent overall rocking and the repairing of the boundary interface to re-establish structural integrity for subsequent testing. The initial results highlight the influence of plan irregularity within the pre-peak behaviour and provide a basis for further exploration in the seismic assessment of irregular, unreinforced masonry buildings.

The application of vibration-based Structural Health Monitoring (SHM) for damage detection is characterised by three fundamental aspects: the features extracted as representative of the structural condition that can be directly linked to some form of damage, the metrics selected as novelty or damage index, and the statistical model or classifier built to identify underlying patterns indicative of changes in the structure's state. Focusing on the first step to improve the performance of vibration-based SHM strategies, the extracted features should be robust to noise, sensitive to the presence of a specific type of damage. Further, damage should induce patterns that are distinguishable from environmental and operational variabilities and other forms of damage such as ageing phenomena. In this paper, the problem is framed as an outlier detection problem and the the use of different modal parameters as Damage Sensitive Features (DSFs) is investigated, evaluating them based on the detection performance of an unsupervised One-Class Support Vector Machine (OCSVM) classifier. In particular, an artificial dataset is generated from the calibrated numerical model of a three-storey steel frame structure in different damage scenarios. The methodology is validated against available experimental data. For the case investigated the natural frequencies were sensitive to damage and robust to noise.

Masonry is one of the most used construction materials for structural and non-structural elements. The number of masonry constructions is still remarkable in countries where the costs of modern technology are high, as masonry solutions remain the most convenient and economical alternatives. Among these countries, unreinforced masonry is usually found in low- and mid-rise buildings, both residential and commercial. Developed countries, however, have favored alternative construction materials like reinforced concrete and steel, while masonry is regarded as an aesthetic and non-structural feature. Most objections to masonry construction are based on its lack of seismic performance. However, a substantial number of well- preserved masonry structures demonstrate that when they are built properly, they can withstand any form of loading, such as wind or seismic loads. Thus, masonry buildings’ seismic performance is underrated and experimental research is necessary to gain insight into their response. The studies available in the literature mainly focus on shake table testing of masonry buildings, while they have not been extensively studied in a quasistatic regimen. In this context, a half-scale two-story unreinforced masonry building with plan irregularity has been tested at the Laboratory of the Structures at the University of Minho. The experimental campaign involves cyclic quasi-static testing with a mode proportional unidirectional loading. Dynamic identification and digital image correlation techniques have been employed to monitor the damage progression. The test has resulted in a rocking response under lateral loading, with a wall detachment from the foundation and slab in the first and second levels, respectively. This paper presents and discusses the experimental procedure and the main outcomes of the study.