ABSTRACT
ABSTRACT: In EN 1991-2 and EN 1990AnnexA2 are set out the rules and limits for a dynamic analysis of structures. In most cases it is sufficient to model the trains as moving axle forces at constant speed. The calculated stresses have to be checked against those derived from load model .LM 71. In addition the bridge deck accelerations are limited to 0.35g for bridges with ballast track. In most cases this criteria appeared to be decisive. This leads to uneconomical designs especially if the limit is slightly exceeded. Measurements on bridges showed that stiffness and damping is underestimated in many cases. A test rig at the Federal Institute for Material Research and Testing (BAM) in Berlin was built to investigate the ballast stability at high accelerations. In addition a mechanical model of the test rig was built by DB Systemtechnik in order to simulate the ballast behaviour. From both laboratory tests and simulations a modified assessment criteria for bridge deck accelerations has been derived. The modified criteria ensure safety against ballast instability and will lead to more economical designs.
