Determination of the dynamic characteristics of railway bridges using different methods

Knowledge of the dynamic characteristics of real railway bridges is particularly important when recalculating existing bridges to accurately model the forced vibration response during train crossing events. A recalculation with simulation of the load case of train crossing may be necessary, for example, due to the planned approval of a new train on the rail infrastructure operator's network. In-situ measurements very often reveal large discrepancies between the dynamic characteristics determined theoretically based solely on planning documents and the values ​​actually found on the structure. There are various reasons for this, which are presented and discussed in this article. The dynamic characteristics of railway bridges consist of their natural frequencies, mode shapes, and system damping. Their measurement can be carried out using various methods, such as the ambient vibration testing method, the analysis of the decay process after train passage, and forced vibrations testing method. In practice, these methods, particularly when determining the bridge's damping ratios, sometimes exhibit very high variances in the results, which can be attributed to various reasons. Hence, this paper experimentally determines the dynamic characteristics of different types of railway bridges (steel, composite, and reinforced concrete bridges) using different methods and compares the variance of the results. Furthermore, the limitations of the different methods for determining the dynamic characteristics are identified and discussed.