Transition Zones for Railway Bridges : A Study of the Sikån Bridge

A transition zone, that is a zone where a railway track leaves its embankment and enters a bridge, is an area of main concern to railway infrastructure managers. An abrupt change in track support stiffness can occur and it is often associated with accelerated rates of degradation of the track and its geometry. Considerable extra maintenance is often required to preserve line, level and ride quality. This extra maintenance increases costs, and often causes delays.A transition slab (also called a link slab) serves as a structural connection between the bridge and the approach embankment. A transition slab is usually supported on one side by the bridge abutment and on the other side by the embankment. Its function is to preserve the track quality and to provide a smooth and safe transition of the trains from the embankment to the bridge structure and vice versa. The aim of this thesis is to study of the effectiveness of the transition slabs in the Sikån Bridge in northern Sweden. The transition zones have been studied during four years from 2008 to 2012. In 2010 transition slabs were installed in order to improve ride quality and to decrease maintenance demand. Track data are based on information collected from Trafikverket (the Swedish Transport Administration) and managed with their software Optram. First a State of the Art of transitions zones is presented. Basic dynamic effects are reviewed as well as track properties and measurement methods. Then an evaluation is made of the behaviour of the track in the transition zone before and after the installation of transition slabs in the Sikån Bridge. Moreover a Life Cycle Cost Analysis (LCCA) has been performed to understand the costs of a bridge of this type. It indicates that the best strategy is to maintain the bridge – rather than to exchange for a new one– as longs as it fulfils load-carrying and safety requirements.The track analysis shows that the installed transition slabs only increased the track performance during the first year after installation. After that the track returned to its earlier conditions. Other ways to improve the transition zone might be to use under-sleeper pads.Validerat; 20140917 (global_studentproject_submitter