A moving-window least squares fitting method for crack detection and rigidity identification of multispan bridges (pages 387–404)

摘要

In this study, a moving-window least squares fitting method is proposed for rapid identification of cracks and flexuralnrigidities in multispan bridges. First, the dynamic deflections of a continuous bridge were locally measurednunder a dynamic point load. Their integrations over time, referred to as ‘integration-over-time deflections’, werenused to derive ‘integration-over-time slopes’. These virtually static measurements over a short segment of thenbridge were then fitted into a cubic curve in the least squares sense. Finally, the coefficient of the square termnof the fitted curve was used to determine both the magnitude and location of local flexibility because of crackingnand/or changing in flexural rigidity of the bridge. For multispan continuous bridges, an iterative procedure wasndeveloped to ensure that the end moments of various spans are compatible with the identified cracks and rigiditynchanges. To illustrate the proposed method, prismatic girder bridges with multiple cracks of various depths or nonprismaticngirder bridges were analyzed. Sensitivity analysis was conducted on the effects of weighting factor, noisenlevel, load type, window length, and bridge discretization. Numerical results demonstrated that the proposednmethod can accurately detect cracks and identify the change in flexural rigidity. The five-point equally weightednalgorithm is recommended for practical applications. The spacing of two discernible cracks is equal to the windownlength. The identified results are insensitive to noise because of integration of the dynamic measurements.nCopyright © 2011 John Wiley & Sons, Ltd.