System identification of cable-stayed bridges under earthquake excitation utilizing post-shaking monitored data

The monitored seismic response data provides useful insight into the dynamic characteristics of cable-stayed bridges during an earthquake shaking. However, the unavailable earthquake input data, as is the case for most cable-stayed bridges, would prevent the system identification using the during-shaking structural response. This study proposes to employ the post-shaking structural response only for system identification of cable-stayed bridges. A 1/20 scaled cable-stayed bridge model under longitudinal shake table accelerations is utilized as a case study for validation. It reveals that the post-shaking seismic response of the scaled cable-stayed bridge is considerably significant. Using the during-shaking data (including the earthquake input) or the post-shaking data (without earthquake input) would yield similar system identification results regardless of the seismic system of the bridge or the characteristics of the input ground motions. The sliding bearings, with pronounced nonlinearity, lead to the variable system identification results of the first sliding mode of the girder but exert a limited influence on the dynamic characteristics of the higher modes. When the ground motions are unknown, the shaking end can be identified within the transition from the nonstationary to stationary response based on the time-frequency analysis of monitored structural responses.