Dynamic FE analysis of a continuous steel railway bridge and comparisons with field measurements

The aim of this paper is to present proper finite element (FE) models which can predict the dynamic characteristics and behaviour of a railway bridge under dynamic train loading for the purposes of fatigue design and assessment. As a case study, an existing six-span continuous welded plate girder railway bridge in Stockholm is investigated. A number of detailed three-dimensional FE models of the bridge are developed in terms of increasing complexity, starting from a beam-only model and refining it to an FE model consisting of shell elements and the combination of the two. Additional factors that are being investigated are the effects of different boundary conditions, the number of modelled spans and the effect of secondary elements such as bracings. Eigenvalue analysis of the bridge is first carried out in order to determine its dynamic characteristics such as dominant frequencies and mode shapes. These are compared between the different models and existing analytical solutions from the literature. Furthermore, available field measurements at different members on the bridge are compared with the results obtained from dynamic time-history analysis under the passage of a typical locomotive at various speeds. Based on the FE analyses on the bridge models and their validation with the field measurements, a number of conclusions and suggestions are made for the advanced dynamic modelling of bridges.