Resonant effects in short span high speed railway bridges: modelling and design issues

Trains at speeds above 200 km/h may induce resonance in bridges or viaducts. This fact implies the necessity of sufficiently detailed dynamic calculations, which has been included in the latest engineering codes of practise ( FS 1997 ; prEN 1991-2 2002; IAPF 2001). Various mathematical models are available for dynamic analysis of trains of moving loads, generally through direct time integration of the equations of motion. Some simplified analytical methods are also available (ERRI D214 (a) 1998) which provide directly dynamic envelopes. However, these methods are only valid for simplysupported beams. In some cases it may be necessary to employ complex models with vehicle-bridge interaction. In this paper we discuss the applicability of the above methods for calculation of railway bridges. Following, two practical studies applying the above techniques are presented. For portal frame underpasses, a simplified method of calculation is justified which may greatly simplify engineering calculations. Finally, we also present results of a study evaluating the relative reduction in dynamic effects which may be obtained by considering vehicle-bridge interaction.