## 1 Introduction
In doing so, a number of problems and doubts arise due to the structural complexity of the studied systems and the lack of information on the dynamic behavior of individual elements, especially if they have a significant impact on the deformation of the structures [19; 20]. Investigating the above-described relationships becomes a key issue for assessing the actual work of the entire structural system and undertaking possible conservation or restoration work. In order to determine the dynamic behavior of a structure, it is necessary to know its modal parameters, which in complex structures are determined using experimental modal analysis [21; 22]. The methodology for determining modal parameters in structures and the basics of applying experimental modal analysis are described in numerous papers [23; 24; 25]. In order to assess the technical condition of a structure or identify its damage, modal analysis is carried out on the basis of an ambient vibration test, in which the dynamic excitation is the actual operating load [26; 27]. The paper [28] compares the results of operational modal analysis (OMA) with those obtained from experimental modal analysis (EMA), which differ in the way the structure is induced to vibrate, either by the actual operating load or by a load applied in a controlled manner, respectively. The advantage of using OMA is that the measurement apparatus itself is sufficient for testing. With EMA, the equipment or device is needed to induce vibrations, which can be difficult or even impossible for large objects. The advantage of EMA is that testing can be carried out at any time, while the use of OMA may require a longer period of time because the excitation load must be large enough. An interesting approach was proposed in a paper [29], where modal analyses were performed based on strain measurements instead of accelerations. Also noteworthy is the work of [30], where modal analyses were carried out taking into account the interaction of the subsoil with the structure. Considering the necessary restoration work related to the possible strengthening of the complex structure of the Domachowo church building, it became a key task to study the work of the entire structural system, as well as to determine the interrelationships and principles of cooperation between the various elements of the structural systems of the walls and the work of the columns. The main purpose of the analyses and research discussed in this paper was to determine the degree of bonding of the branches of the wooden column composed of three elements made at different times, i.e., in different historical periods, in which the analyzed building of the Domachowo church was built. Based on the results of the dynamic analysis, it can be concluded that the degree of bonding and cooperation of the branches has an impact on the entire structure of the church building. Assuming that the branches of the column are rigidly connected to each other at several points, lower values of stresses occurring during the action of wind are obtained, which is of great importance for the stability of the entire structure and for making possible decisions on its possible reinforcement. The article begins with a brief description of the building under study and the measurement techniques used, including traditional surveying methods and measurements made with inclinometers. The next part of the article describes how the experimental modal analysis was carried out and discusses the results obtained from the study of selected multi-branch columns. The created numerical model of the building structure is also described, and the results of the static and dynamic analyses, which were obtained taking into account or omitting the stiffening panels of the bar structure, are given. At the end, a summary containing conclusions of the conducted research and planned strengthening works is presented.