System identification of highway bridges from ambientvibration using subspace stochastic realization theories

摘要

In this study, the subspace stochastic realization theories (SSR model I and SSR model II)have been applied to a real bridge for estimating its dynamic characteristics (natural frequencies, dampingconstants, and vibration modes) under ambient vibration. A numerical simulation is carried out for anarch-type steel truss bridge using a white noise excitation. The estimates obtained from this simulation arecompared with those obtained from the Finite Element (FE) analysis, demonstrating good agreement andclarifying the excellent performance of this method in estimating the structural dynamic characteristics.Subsequently, these methods are applied to the vibration induced by both strong and weak winds asobtained by remote monitoring of the Kabashima bridge (an arch-type steel truss bridge of length 136 m,and situated in Nagasaki city). The results obtained with this experimental data reveal that more accurateestimates are obtained when strong wind vibration data is used. In contrast, the vibration data obtainedfrom weak wind provides accurate estimates at lower frequencies, and inaccurate accuracy for highermodes of vibration that do not get excited by the wind of lower intensity. On the basis of the identifiedresults obtained using both simulated data and monitored data from a real bridge, it is determined that theSSR model II realizes more accurate results than the SSR model I. In general, the approach investigatedin this study is found to provide acceptable estimates of the dynamic characteristics of highway bridges aswell as for the vibration monitoring of bridges.