Semi-active damping systems for railway bridges

In this paper, a semi-active control system for vibration mitigation of railway bridges is presented. The real time frequency response is estimated using a short-time Fourier transform, employing curve fitting to relevant peaks for increased accuracy. A control algorithm developed in MATLAB® is linked to a commercial FE-software, facilitating application on arbitrary structures. A numerical study of an existing tied arch railway bridge is presented. From earlier field measurements and numerical analysis, resonance of several hangers during train passage was observed. This was shown to significantly reduce the fatigue service life of the hangers and for the most critical section about 50% of the cumulative damage was related to free vibrations. A system of passive dampers was later installed and the increase in resulting damping was measured. Within the present study, the previous results are reanalysed and compared with a semi-active approach. The natural frequencies of the hangers vary as a result of the variation in axial force. A semi-active control system has the potential to improve the vibration response of the structure when compared to the installed passive system.