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As computers carry out increasingly complex tasks and perform the brunt of the work for any given analysis, it is becoming more important to create computer models with an appropriate level of detail. The balance between the detail of a computer model, which in turn improves the accuracy of the analysis, against the resulting increase in time and effort can be difficult to achieve. This research analyses the dynamic response of a high-speed rail vehicle crossing a case study bridge structure at various levels of loading model detail, beginning with a “moving force”, and then gradually increasing in complexity with a “moving mass” and a “moving oscillator”. Increasing the complexity of the load model firstly takes into consideration the variation of the inertia while the vehicle crosses the bridge and secondly the dynamic interaction between the vehicle and the bridge.

Currently the Eurocodes, the basis for all structural design across Europe, does not require the designer to account for either of these dynamic phenomenon, but only to model the dynamic effects of a train as a series of travelling point forces (§6.4.6.4 BS EN 1991-1:2003). This research poses the question, is that assumption acceptable?

The analyses will be performed using the commercial structural analysis program SAP 2000 and the numerical suite MatLab. The use of two programs increases the control over the modelling process and allows for the disconnection of the model creation from the dynamic analyses. Part of the model creation is undertaken in SAP2000, which models the required bridge properties. This information is then imported into MatLab, which models the dynamic loading regime (the train loading) and undertakes the dynamic analyses.

To highlight the impact of the results, a fatigue assessment will be undertaken at all three levels of detail using Miner’s rule in conjunction with the rainflow counting algorithm. The results will determine whether the increased level of detail in the dynamic load model is warranted.