## 1 Introduction  
During the past few decades, natural hazards such as earthquakes have remained as one of the grand challenges in structural and earthquake engineering. These challenges have led to an increasing emphasis on structural assessment and health monitoring to evaluate the structural conditions and gave recommendations for further procedures related to the renovation, rehabilitation, and maintenance of buildings. During such hazards, masonry buildings, which were mostly built at a time when there were no legal regulations for the design of seismically resistant buildings, take a _significant hit_ (a series of damages and collapses). Due to the lack of the knowledge about their condition and mechanical properties, experimental investigation plays an important role. To evaluate the performance of such structures, different damage assessment methods based on the qualitative and/or quantitative data have been developed [1; 2; 3; 4; 5; 6; 7]. The main aim of them is an identification of the existence, location, and severity of the damage and estimation of the remaining structural life. In addition, the experimental investigations are important segment for numerical modelling of existing structures [8]. Combining it with numerical modelling is often used to obtain the real structural behaviour numerically and interpretate it with ideal boundary conditions and constitute materials [9; 10]. The whole process of improving the numerical model according to the experimental investigation test results is performed as a part of finite element model updating (FEMU) procedure [11]. The FEMU process is based on the iteratively updating the design variables (material properties, geometry, boundary conditions, etc.) to obtain the experimental investigation test results numerically [12]. The experimental investigations that are performed most frequently include the dynamic test, i.e., determination of natural frequencies and mode shapes [13]. These parameters are the best indicators of any changes on structure. If there are any changes in form of damage that could affect the change in stiffness, it will also affect the change in natural frequencies and mode shapes [14]. On the other hand, if we move to the local level of the model and the mechanical properties of the materials of structural systems such as masonry buildings, a series of laboratory and field tests are carried out. They usually include shear tests [15], tensile tests [16], flat jack tests [17], and other destructive [8] and non-destructive [18] tests. Performing these tests, shear and compressive strength, vertical stress, modulus of elasticity, relationship between deformation, and other mechanical properties can be obtained. They become a very important source of information for designers. The research focuses on assessing the dynamic parameters of masonry buildings prior to earthquakes, with a novel approach combining experimental investigations and numerical analysis. The study aims to quantify the changes in dynamic parameters, such as natural frequencies and mode shapes, providing valuable insights into the response characteristics of damaged masonry buildings. The paper discusses the potential masking of severe damage by other factors that influence the alteration of dynamic parameters, highlighting the need for a comprehensive understanding of the dynamic behavior of masonry structures before seismic events. Through iterative model updating, including modifications to boundary conditions, partition walls, damages, and global stiffness, the researchers successfully improve the numerical model's accuracy in describing the current structural condition. The resulting model allows for the creation of a behavior model that describes the structure before earthquake-induced damage, contributing to improved structural condition assessment and effective mitigation strategies. The paper is organized as follows: the Section 2 provides an analysis of the structural dynamic properties' changes due to seismic action.