Railway bridge response to passing trains : Measurements and FE model updating

Abstract: Today’s railway bridges are analysed in more detail for moving loads due to the increase in speeds and axle loads. However, these numerical analyses are very time consuming as they often involve many simulations using different train configurations passing at different speeds and many considerations to take into account. Thus, simplified bridge, track and train models are often chosen for practical and time efficient simulations.The New Årsta Railway Bridge in Stockholm was successfully instrumented during construction. A simplified 3D Bernoulli-Euler beam element FE model of the bridge was prepared. The FE model was first manually tuned based on static load testing. The most extensive work was performed in a statistical identification of significantly influencing modelling parameters. Consequently, parameters to be included in an optimised FE model updating, with consideration also to synergy effects, could be identified. The amount of parameters included in the optimisation was in this way kept at an optimally low level. For verification, measurements from several static and dynamic field tests with a fully loaded macadam train and Swedish Rc6 locomotives were used. The implemented algorithms were shown to operate efficiently and the accuracy in static and dynamic load effect predictions was shown to be considerably improved.It was concluded that the complex bridge can be simplified by means of beam theory and an equivalent modulus of elasticity, and still produce reliable results for simplified global analyses. The typical value of an equivalent modulus of elasticity was in this case approximately 25% larger than the specified mean value for the concrete grade in question.The optimised FE model was used in moving load simulations with high speed train loads according to the design codes. Typically, the calculated vertical acceleration of the bridge deck was much lower than the specified allowable code value. This indicates that multispan continuous concrete bridges are not so sensitive to train induced vibrations and therefore may be suitable for high speed train traffic.Finally, the relevant area of introducing the proposed FE model updating procedure in the early bridge design phase is outlined.