Analysis of combined response of railway bridge and track : A parametric finite element model of the bridge across Bryngeån

Abstract: When designing a railway bridge it is common to consider and designthe bridge structure and the track structure separately. However, theyare connected and that interaction generates a combined response and aforce transfer between them. In addition, the common rail type of today,continuously welded rails, are continuous over the discontinuity between thedeck and embankment. This provides a connection also to the embankmentsand therefore an additional force transfer. The combined response gives riseto additional stresses and forces in the structures that need to be taken intoaccount.This is done in Eurocode 1991-2 by limiting values of stresses anddisplacements. The basis for these values were created in the second half ofthe 20:th century, considering ballasted tracks. However, with changes in thetrack design, the characteristics of the materials and available computationalmethods, there are indications that the basis for the limiting values are to someextent outdated and that there is a need of an updated design practice.Within this thesis, a parametric finite element model analysing the stresses,displacements and forces created due to track and bridge interaction, TBI, hasbeen developed. The model has then been used to analyse a simply supportedsteel-concrete composite bridge. This bridge is located outside Örnsköldsvikin the northeast part of Sweden, spanning across Bryngeån.The simulations show that the bridge does not exceed the limiting valuesfor the stresses, reaching 80 MPa in tension and 66 MPa in compression.However, increasing the span length from 48 m to 51 m, the compressive stressreaches 71 MPa, just shy of the limit value of 72 MPa.The design value of the reaction force in the fixed support for this bridgehas increased with 66% since the bridge was built. In comparison, thereaction forces obtained from the combined response, with contributions froma temperature difference between the deck and the rail, a vertical load picturedby LM 71 and a traction force, reach values of 100% to 230% of the designvalue used when the bridge was designed. The largest contribution comesfrom the vertical load due to the distance between the bearings and the neutrallayer of the deck.