Light rail traffic presents significant advantages in a heavy populated urban environment in terms of quality of service, volume of passengers, delays etc. Vibrations caused by tramway vehicles passing through highly populated urban areas present a great impact on the quality of life of citizens. Beside the life quality, severe vibrations can also influence structural integrity of surrounding buildings and other infrastructure. In a crowded urban environment, underground structures such as underpasses, garages or water supply and sewage facilities are often located directly under the rail track structures. In such scenarios, special attention has to be pointed to track design in terms of vibration attenuation, as well as underground structure design in respect to additional dynamical loads presented by the overhead rail traffic. The paper presents a case-study of vibration measurement and analysis on an underground garage constructed under a tramway line on Kvaternik square in Zagreb. Rail discontinuities at turnouts and crossings present an impact point between tram vehicles and the track and therefore induce severe vibrations. To analyse tram induced vibrations and its effects on
an underground garage structure, measurements on several locations have been conducted, including square surface and underground garage slab structures. Measurements have been conducted immediately after the construction of the garage and tram track on top of it, and repeated after 6 years of exploitation, using same principles and under same traffic load. This way the influence of exploitation wear and aging could be evaluated and analysed. Additionally, vibrations in the working environment of underground garage staff have also been considered. Such practice of periodical vibration measurements serves as an early warning system for any unexpected structural defects and provides a tool for future decision making and maintenance works scheduling.

floating slab track, tram, vibrations, underground garage, exploitation