A Multiple Random Decrement Method for Modal Parameter Identification of Stay Cables Based on Ambient Vibration Signals

The cables of cable-stayed bridges are the primary force-transmitting members of the whole structure and consequently play an important role in reflecting the dynamic characteristics and health condition of the total bridge system. The dynamic response of the cable generally attributes to numerous lower modes because of its low flexural stiffness. Accordingly, the parameters of more modes are usually required for stay cables than other civil structures. It is aimed in this study to develop an effective method for accurately identifying the parameters of various cable modes merely based on the ambient vibration measurement of a single sensor installed on each cable. A mode separation technique is first introduced to extract the independent contributions to the measured signal of cable from individual modes. A multiple random decrement method is further developed to completely exclude the excitation effect and extract the free vibration response. With the combination of the above two techniques, convenient identification techniques such as the Ibrahim time domain method can then be applied to independently identify the individual parameters for each mode. The whole methodology is demonstrated by applying it to the ambient velocity measurements for the cables of Chi-Lu Bridge. Imitating the identified parameter values from the actual measurements, SAP200 models for three different types of cable are constructed to simulate the ambient vibration signals. These simulated signals are finally used for identification to verify the effectiveness and accuracy of this method.