Zum Einfluss baulicher Randbedingungen auf das dynamische Verhalten von WIB-Eisenbahnbrücken
- On the influence of constructional elements on the dynamic behaviour of filler beam railway bridges
Rauert, Tim; Feldmann, Markus (Thesis advisor)
Aachen : Publikationsserver der RWTH Aachen University (2011)
Dissertation / PhD Thesis
Aachen, Techn. Hochsch., Diss., 2011
Enhancements of the European railway system are amongst other things mainly characterized by increased usage of high speed trains and significantly raised operating speeds. To predict effects of train loading on railway bridges for a dynamic design adequately, knowledge of the system’s significant dynamic characteristics is required. Only this ensures that resonance effects, which generally cannot be screened out for high speeds, can be covered analytically by reliable values. Measurements especially carried out on filler beam bridges have shown though that a realistic estimation of eigenfrequencies of bridges is difficult. Actual values and measured ones differ significantly in many cases. In particular non-consideration of structural constraints is seen as reason for this, given that they have an immense effect on a bridge’s stiffness and damping characteristics. Within the scope of this thesis, firstly measurement campaigns on various filler beam bridges were conducted and analysed, in order to study the range of constructional detailing with regard to span lengths, cross-section design, bearings and additional non supporting structural elements on the bridge deck, furthermore in order to investigate the influence of these structural constraints on the bridge’s dynamic behaviour. The above mentioned experiences were confirmed by the obtained measurement results. Based on this, finite element calculations were carried out to simulate train passages with high velocities on filler beam bridges. These numerical studies aimed at both qualitative and quantitative assessment of dynamic effects resulting from the most influential constraints. For being able to consider interaction effects numerically, caused by continuous ballast layers on separated bridge decks, experimental tests on railway ballast were conducted. The outcome of these tests is a simplified mechanical model that can be applied in numerical calculations for taking into account the load transfer between ballast-connected structures. The numerical investigations revealed that stiffness contributions of non supporting concrete elements, attached to the cross section, have significant influence on the bridge dynamics, particularly in case of small span lengths. Furthermore it was ascertained that all effects on the system rigidity, resulting from the various structural constraints, can be considered in a similar way within numerical analysis - by increasing the cross section’s global bending stiffness. The evaluation of the measurement campaigns as well as the results from the experimental and numerical investigations lead to proposals for an improved dynamic bridge design. A design tool was prepared in order to determine the effective bending stiffness of filler beam decks approximately. It is based on correction factors to modify calculated stiffness values. By using this design tool, the prediction of the dynamic behaviour of filler beam bridges becomes more reliable. The procedure can easily be included within the current design practise which is finally shown by means of an example of dynamic bridge design.