Kalman Filter-Based Identification of Bridge Fragility Parameters

The study describes a procedure to identify bridge fragility parameters utilizing its vibration response recorded during experimental study. For this purpose, bridge damage data observed in a near full-scale shake table experiment is utilized. The bridge was tested under a sequence of earthquake ground motions with increasing intensities. Low and high amplitude tests were performed in series to observe the seismic performance of the bridge starting from yielding to complete failure. In the present study, recorded bridge acceleration during high amplitude tests is utilized and further analyzed to evaluate the degraded performance of the bridge after each high amplitude test. This is done by using extended Kalman filtering (EKF) technique as a tool. The degraded performance of the bridge after each run is measured in terms of degraded stiffness of the bridge at pier ends. In parallel, finite element (FE) model of the same bridge is developed in order to perform time history analysis under a set of earthquake ground motions with various hazard levels. Before applying the ground motions, the FE model is updated with the degraded stiffness of the bridge obtained from EKF after each high amplitude test. This is important to numerically simulate the gradual progression of bridge damage when subjected to earthquake ground motions in sequence. After each time history analysis, bridge response is obtained in terms of the rotation at bridge pier ends. Thus obtained response from time history analyses is used for fragility curve development. The change in fragility parameters represents the progressive damage of the bridge when subjected to ground motions with incremental intensity.