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Long-term behaviour of railway transitions under dynamic loading application to soft soil sites
Dissertação para obtenção do Grau de Doutor em Engenharia Civil ; Transition zones in railway tracks are built to mitigate damage and wear to tracks and trains, and discomfort to passengers, caused by structural and foundation discontinuities, such as those introduced by bridge approaches or culverts. However, additional strains are still generated that cause changes of track geometry, that lead to more frequent maintenance operations and sometimes speed restrictions, that raise costs, and need to be minimized. This thesis addresses those questions and describes research undertaken to model the dynamic response of the railway tracks, taking into account the behaviour of ballast at the aforementioned railway transition zones, where the long-term settlements are amplified by dynamical loading on the ballast due to the discontinuities. Novel numerical models for the simulation of the dynamic response of the system soilballast-track-vehicle and accounting for those phenomena are presented. The models are validated by field measurements performed at a passage over a culvert, located in a soft soil site. The models include the unloaded level of the track, the possibility of voids under the sleepers, and the non-linear constitutive behaviour of the ballast, as well as representation, albeit simplified, of the vehicles. The forces transmitted to the ballast at transition areas vary considerably, both in time and space: loading of ballast reaches higher values than in regular tracks, and the additional vibrations cause larger differences between loads transmitted to consecutive sleepers. This causes higher densification of ballast at transition zones. Transition zones solely composed of approach slabs are not effective in soft soil sites. The soil and ballast at approach regions settle more than the segment on top of the much stiffer structure, leading to the appearance of hanging sleepers. The subsequent combined effect of lower load on part of the ballast and motion of the approach slabs results on increased settlement ...
Long-term behaviour of railway transitions under dynamic loading application to soft soil sites
Dissertação para obtenção do Grau de Doutor em Engenharia Civil ; Transition zones in railway tracks are built to mitigate damage and wear to tracks and trains, and discomfort to passengers, caused by structural and foundation discontinuities, such as those introduced by bridge approaches or culverts. However, additional strains are still generated that cause changes of track geometry, that lead to more frequent maintenance operations and sometimes speed restrictions, that raise costs, and need to be minimized. This thesis addresses those questions and describes research undertaken to model the dynamic response of the railway tracks, taking into account the behaviour of ballast at the aforementioned railway transition zones, where the long-term settlements are amplified by dynamical loading on the ballast due to the discontinuities. Novel numerical models for the simulation of the dynamic response of the system soilballast-track-vehicle and accounting for those phenomena are presented. The models are validated by field measurements performed at a passage over a culvert, located in a soft soil site. The models include the unloaded level of the track, the possibility of voids under the sleepers, and the non-linear constitutive behaviour of the ballast, as well as representation, albeit simplified, of the vehicles. The forces transmitted to the ballast at transition areas vary considerably, both in time and space: loading of ballast reaches higher values than in regular tracks, and the additional vibrations cause larger differences between loads transmitted to consecutive sleepers. This causes higher densification of ballast at transition zones. Transition zones solely composed of approach slabs are not effective in soft soil sites. The soil and ballast at approach regions settle more than the segment on top of the much stiffer structure, leading to the appearance of hanging sleepers. The subsequent combined effect of lower load on part of the ballast and motion of the approach slabs results on increased settlement ...
Long-term behaviour of railway transitions under dynamic loading application to soft soil sites
Ferreira, José Nuno Varandas da Silva (Autor:in) / Silva, Manuel / Hölscher, Paul
01.01.2013
101272103
Hochschulschrift
Elektronische Ressource
Englisch
DDC:
624
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