Structural Identification and Damage Detection in Bridges using Wave Method and Uniform Shear Beam Models: A Feasibility Study

This report presents a wave method to be used for the structural identification and damage detection of structural components in bridges, e.g., bridge piers. This method has proven to be promising when applied to real structures and large amplitude responses in buildings (e.g., mid-rise and high-rise buildings). This study is the first application of the method to damaged bridge structures. The bridge identification was performed using wave propagation in a simple uniform shear beam model. The method identifies a wave velocity for the structure by fitting an equivalent uniform shear beam model to the impulse response functions of the recorded earthquake response. The structural damage is detected by measuring changes in the identified velocities from one damaging event to another. The method uses the acceleration response recorded in the structure to detect damage. In this study, the acceleration response from a shake-table four-span bridge tested to failure was used. Pairs of sensors were identified to represent a specific wave passage in the bridge. Wave velocities were identified for several sensor pairs and various shaking intensities are reported; further, actual observed damage in the bridge was compared with the detected reductions in the identified velocities. The results show that the identified shear wave velocities presented a decreasing trend as the shaking intensity was increased, and the average percentage reduction in the velocities was consistent with the overall observed damage in the bridge. However, there was no clear correlation between a specific wave passage and the observed reduction in the velocities. This indicates that the uniform shear beam model was too simple to localize the damage in the bridge. Instead, it provides a proxy for the overall extent of change in the response due to damage

Structural Identification and Damage Detection in Bridges Using Wave Method and Uniform Shear Beam Models: Application to a Shake-Table Tested Bridge

This thesis will present a wave method to be used for the identification of the structural system and damage detection of structural components in bridges. This method was shown to be strong when applied to real structures and large amplitude response in buildings (e.g., mid-rise and high-rise buildings). This study is the first application of the method to bridge structures. The bridge identification was performed using wave propagation in a simple uniform shear beam model. The method identifies a wave velocity for the structure by fitting an equivalent uniform shear beam model in impulse response functions of the recorded earthquake response. The structural damage is detected by detecting changes in the identified velocities from one damaging event to another. The method uses response of the acceleration recorded in the structure. In this study, the acceleration response from a shake-table 4-span bridge tested to failure was used. As the information was available on the shake-table test data, it provided us an opportunity to check the accuracy of our uniform shear beam model’s identification results. It also revealed the strength and limitation of the shear beam model for damage detection in bridges. The prototype bridge was instrumented using nine triaxial accelerometers at the deck level and three triaxial accelerometers at the base of its columns (i.e., shake-tables). A uniform shear beam model can be identified using data from two channels (source and receiver). Unlike building structures which typically comprise sensors placed on their floors (along their height), the sensor placement on a bridge comprises a two-dimensional distribution (along the height and length of the bridge). Therefore, two scenarios for wave propagation in the bridge were proposed. In each scenario, pairs of sensors were identified to represent a specific wave passage in the bridge. Identified wave velocities for each scenario and for various shaking intensities were reported. A summary of actual observed damages in the structure was prepared. The observed damages were then grouped into five damage states. Further, damage states were compared with the detected reductions in the identified velocities. The results show that: 1) The identified shear wave velocities presented a decreasing trend as the shaking intensity was increased, 2) the reduction percentage in the velocities was consistent with the overall observed damage in the bridge, 3) there was no clear correlation between a specific wave-passage and the observed reduction in the velocities. This indicates that the uniform shear beam model was too simple to localize the damage in the bridge. It rather provides a proxy on the extent of complete change in the response due to damage. While the shear beam model provided a unique opportunity for extending the wave method application to the bridge structure, it revealed that a more detailed model will be required to take into account the bending nature of bridge response and the significant wave dispersion associated with it. Further study will be needed for developing and calibrating a more detailed model for the purpose of a robust damage detection and damage localization in bridges