Abstract Summary
With increasing axle loads and train speeds, predicting the dynamic behavior of railway bridges under high-speed traffic plays an increasingly important role in assessing bridge structures. However, the discrepancy between vibrations measured on structures and those predicted by calculations reveals the insufficient modeling depth of simple calculation models, which are primarily applied when there is a lack of reliable information about the structures and the passing trains. In particular, the computational acceleration results often significantly overestimate reality, which can be attributed to the fact that beneficial influences are often omitted in favor of straightforward calculation models. More realistic results can be obtained by considering the interaction dynamics between the train masses, superstructure, and supporting structure. With this, precise knowledge of coupling properties has a central role as they significantly influence the calculated vibrations. When taking vehicle bridge interaction into account by multi-body modeling of the train, the access to information on train properties is often kept secret by manufacturers due to economic interests. Therefore, the present contribution focuses on the influence of modeling the bridge structures as coupling beams, i.e., by considering them as two vertically coupled beams representing the track (rails and sleepers) and the supporting structure. Both beams are interconnected vertically by Kelvin Voigt elements, whose stiffness and damping properties reflect those of the ballasted superstructure. The equation of motion of the proposed model is approximated using trigonometric shape functions and solved by numerical time step integration, whereby the system can be dynamically exerted by moving load models as well as multi-body models of the train. A computational parameter study is carried out with a locomotive-hauled Railjet over a wide range of realistic combinations of single-span girder bridge characteristics: span, natural frequency, mass distribution, and assumed coupling stiffness representing the load distribution capacity of the ballast bed. The calculation results are subsequently compared with the ones of a reference simple beam model. The vertical structural acceleration at midspan is used as a comparative criterion. The evaluation of results enables identifying the structural properties for which applying coupling beam models has a particularly significant influence on the maximum accelerations and quantifying that influence. Additionally, it is examined to what extent the influence of the coupling beam modeling depends on the chosen train model. The analyses demonstrate the potential for obtaining lower acceleration results by considering the load-distributing impact of the ballasted superstructure in coupling beam models (facilitating verification of compliance with normative acceleration limits). They indicate that the influence of multi-body models of the train, which consider vehicle bridge interaction, is particularly pronounced for different structures than that of the coupling beam modeling. These findings open up the possibility of formulating structure-dependent recommendations concerning the targeted application of more complex modeling of the structure (coupling beam model) on the one hand and train (multi-body model) on the other. Thus, they enable a realistic calculational prediction of the structural vibrations independent of vehicle information for the greatest possible share of structures.
