Output-Only Modal Analysis of Malahide Viaduct Bridge

This paper investigates identifying the natural frequencies of Malahide viaduct bridge, which is located in north of Dublin, using vibration data collected on an in-service train. The bridge has 12 spans and is located at Dublin-Belfast line. Acceleration data are collected from accelerometers installed on steel rails attached to the bridge. As there were only 5 wireless accelerometers available, a multi-stage approach is developed to cover all the spans. The natural frequencies of each span are calculated using the vibration data collected during the train passage (forced vibration) and after it (free vibration). It is shown that the natural frequencies of most of the spans are within in similar range, except the ones which are replaced after a collapse in 2008.