Structural assessment of a cable-stayed bridge

The structural health monitoring of a large cable-stayed bridge using ambient vibration measurement is summarized. The location of the bridge cannot, at this time, be revealed for confidentiality reason. The bridge is continuously monitored with an instrumentation system that has been collecting 16 channels of acceleration, wind pressure and temperature data over the past six years. The paper focuses on the analysis of two data sets collected in June 1995 and September 2000. Nonlinear data processing techniques such as higher-order statistical and temporal moments and wavelet transforms are presented to quantify the energy content of the signals in the time and frequency domains. Then, linear modal models are fit to the data in order to translate the changes observed in terms of stiffness reduction or damping increase. It is concluded that structural change takes the form of a reduction in stiffness rather than an increase in damping. The discussion also illustrates typical issues encountered in structural health monitoring applications. These include collecting non-stationary signals, investigating a nonlinear response and dealing with environmental variability and changing operating conditions.