During vibrations, the structure passes through different behavior areas (elastic or inelastic). Different areas of behavior correspond to different approaches to analysis and design. Modeling vibrations as a phenomenon includes its presentation in the form of a mathematical model, with certain parameters specific to the system, which define and control the vibration process itself, namely mass, stiffness and damping. While mass and stiffness can be more accurately described mathematically, damping modeling involves the state and medium in which the system resides. Due to differences in understanding of the state variables that control damping forces, there is still no single accepted model of damping. The wrong selection of damping model in the dynamic analysis of structures can result in the response of the structure being underestimated, which can be the cause of the collapse of the structure. The paper analyzed the response of the bridge structure to pedestrian excitation, applying different numerical damping models and the damping determined experimentally. At the end of the paper, a comparative analysis with conclusions is given.

The paper provides an overview of ambient vibration tests and numerical analysis performed in the framework of Project NATO SfP 983828. The aim of the research is the definition of the dynamic characteristics of bridges on the examples. The paper considers three case studies: two older existing bridges and one newly constructed bridge. A comparative analysis of natural frequencies and mode shapes, obtained by ambient vibration measurements (AVM) and mathematical models (AMs), was carried with the aim to demonstrate the usefulness of ambient vibration tests for identification of the modal parameters of the tested bridge structure. Agreement between AVM and AMs results is very good. The mode shapes are very similar. Some differences between computed and measured frequencies were obtained, which can be attributed to the real nature of the boundary conditions, the uncertainty in the material properties of structure elements, and the mathematical models assumptions.