Modal parameter identification for a GFRP pedestrian bridge

Dynamic experiments were conducted on an all-FRP composite pedestrian bridge. The structure was excited by impact and human-induced vibrations. The peak-picking method and stochastic subspace identification method were used to extract structural dynamic characteristics without knowing the input excitation. Both methods proved to be applicable as output-only methods in situ and in real time. Better results were obtained from ambient excitation than from impact excitation. The joint types used in the truss structure – bolted joints in one span and adhesively bonded joints in the other span – markedly influenced the dynamic behavior of the two spans. The lowest natural frequency resulted from the first lateral mode and was 26–28% smaller for the bolted span than for the bonded span. The bolted span, however, exhibited higher damping ratios than the bonded span due to friction in the bolted joints. The resulting natural frequencies for the tested structure were of the same order of magnitude as for other FRP bridges.