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.

Original scientific paper An overview of research performed in the framework of the NATO Project SfP 983828 is given in the paper. The scope of the research was to identify the parameters affecting the dynamic response of an existing R/C girder bridge, based on ambient vibration measurements and numerical simulations using finite element models (FEM). For this purpose, the bridge across the river Bosnia near Sarajevo and the soil surrounding the bridge were instrumented. Ambient vibration tests and geophysical investigations were performed. The results are studied and a refined three-dimensional (3D) FEM is developed that takes into consideration the soil-structure interaction and superstructure-substructure interaction. The FEM’s with designed parameters and parameters obtained by measurements were developed. The developed FEM models are comparatively assessed and FEM model with congruence between the measured and computationally predicted dynamic characteristics of the structure was defined. The results of the analysis show that the adequate determination of the pier, deck and bearings stiffness is the key parameter for reliable system identification.