In railway bridge dynamics, the accurate prediction of deck accelerations is essential to ensure ballast stability, track quality, and the overall structural integrity of the bridge. Adequate modelling of the track, bridge, and subsoil is often a difficult challenge due to the conflicting requirements of accuracy and efficiency of the chosen modeling approach. Therefore, the modeling approaches found in the literature often focus either on efficiency by making simplifying assumptions about the foundation, the subsoil, the track and the bridge, or on accuracy by modeling of the geometry and material of the structural components and the subsoil in detail. The objective of this contribution is to assess the reliability of an efficient modelling strategy that includes the track, bridge, and foundation on the subsoil in the form of a simple two-dimensional lumped parameter model in comparison to a sophisticated, fully three-dimensional transient coupled finite element – boundary element approach. The fundamental modal properties of both models and their respective subsystems are evaluated and used to optimize the simplified approach. Special emphasis is placed on the accurate consideration of the dissipative effect of propagating waves in the infinite domain of the soil. Final conclusions regarding the applicability as well as the limitations of the simplified approach are drawn from the comparison of the acceleration response predictions due to the passage of a train for both models.

A high-speed train passing a bridge structure at a critical speed can induce large bridge vibrations. In particular, the acceleration of the bridge deck is a critical design parameter because exceeding the normative limit can cause ballast instability resulting in track misalignments. Therefore, it is of utmost importance to realistically predict the acceleration response of the bridge in the design process based on a sufficiently accurate yet computationally efficient mechanical model. In engineering practice and research, a variety of modeling strategies exist with varying degrees of sophistication. For the structure, these can range from simply supported Euler-Bernoulli beam models that capture the bridge to two beams representing the structure and the track separately that are coupled by vertical and horizontal spring-damper elements, to sophisticated 3D finite element models that capture the components of the bridge and the track (and possibly the subsoil) in detail. The train modeling strategy ranges from single loads to detailed train models with multiple DOFs. Many bridges are single-span structures, but especially high-speed railway bridges span large valleys and thus consist of several single-span structures of the same length, weakly coupled by the superstructure of ballast and rail. The objective of this study is to evaluate the effect of different modelling strategies on the numerical prediction of the dynamic response of such weakly coupled ballasted bridge structures. In particular, different beam models with and without soil-structure-track interaction as well as with and without consideration of the weak coupling between the adjacent bridge structures are considered. The results of deterministic (semi-probabilistic) analyses and probabilistic failure assessments are performed and compared for the different models.