Variation of modal parameter estimates of a prestressed concrete bridge

This paper presents the processing methods and the analysis results of ambient vibration data recorded during a sixmonth period on a highway bridge. Data analysis was focused on the variations of the modal parameter related to the accuracy of the estimates and to the temperature effects. The first flexural and torsional modes were estimated with their variance from short acceleration time series records using stochastic covariance driven subspace identification techniques. The frequency variation estimates were compared to the variations induced by structural modifications simulated with a finite element model for assessing the detection threshold level. Subsequently the temperature induced variations in the measured frequencies were analysed. Results of a damage detection test based on the computation of a null-space residual derived from the covariance estimates show the response to the temperature effects. Significant increases in the variance of the parameter estimates were also detected by the test. Finally, the effectiveness of the temperature robust version of this promising damage detection method was investigated with the available data records.