Investigation of changes in modal characteristics before and after damage of a railway bridge: a case study

摘要

The linear, time-invariant transfer function T_(xy) has been utilised for the construction of frequency response function , based on the ambient vibration measurements. The results presented here indicated the possibility to identify and localise damages in steel railway bridges from the variations in the modal characteristics of the structure. The comparison between the modal characteristics for the healthy and collapsed bridge confirmed that damage had been existed. The abnormal percentage of change in modal damping, between the healthy and any other condition for a structure, can be regarded as a serious indicator for early stages of damage, while the high percentage of change in modal damping can clearly indicate the existence of damage in that structure. The average ratio of change in the damping ratio from the healthy to the collapsed bridge was about 206% and this ratio could be regarded as an index for the existence of a serious damage in steel bridges, which needs further evaluation in other test cases.