Abstract
Displacement monitoring of large bridges is an important source of information concerning their health state. In this paper, a procedure based on satellite Persistent Scatterer Interferometry (PSI) data is presented to assess bridge health. The proposed approach periodically assesses the displacements of a bridge in order to detect abnormal displacements at any position of the bridge. To demonstrate its performances, the displacement characteristics of two bridges, the Nanjing-Dashengguan High-speed Railway Bridge (NDHRB, 1272 m long) and the Nanjing-Yangtze River Bridge (NYRB, 1576-m long), are studied. For this purpose, two independent Sentinel-1 SAR datasets were used, covering a two-year period with 75 and 66 images, respectively, providing very similar results. During the observed period, the two bridges underwent no actual displacements: thermal dilation displacements were dominant. For NDHRB, the total thermal dilation parameter from the PSI analysis was computed using the two different datasets; the difference of the two computations was 0.09 mm/°C, which, assuming a temperature variation of 30 °C, corresponds to a discrepancy of 2.7 mm over the total bridge length. From the total thermal dilation parameters, the coefficients of thermal expansion (CTE) were calculated, which were 11.26 × 10−6/°C and 11.19 × 10−6/°C, respectively. These values match the bridge metal properties. For NYRB, the estimated CTE was 10.46 × 10−6/°C, which also matches the bridge metal properties (11.26 × 10−6/°C). Based on a statistical analysis of the PSI topographic errors of NDHRB, pixels on the bridge deck were selected, and displacement models covering the entire NDHRB were established using the two track datasets; the model was validated on the six piers with an absolute mean error of 0.25 mm/°C. Finally, the health state of NDHRB was evaluated with four more images using the estimated models, and no abnormal displacements were found.
Highlights
The long-term millimeter-level displacement monitoring of man-made structures, such as dams, embankments, bridges, and railways, is a promising field of application for satellite Persistent Scatterer Interferometry (PSI)
The distribution of the topographic error is similar in both cases: as seen below, both include a uniform distribution, which corresponds to the bridge arcs, and a normal distribution, which is related to the other part of the bridge
The diversity of the PS density can be explained by the fact that the upper layer of the Nanjing-Yangtze River Bridge (NYRB) is a highway that is relatively flat for C-band radar signal, while the lower part of the bridge, constructed with metal truss, has strong backscattering
Summary
The long-term millimeter-level displacement monitoring of man-made structures, such as dams, embankments, bridges, and railways, is a promising field of application for satellite Persistent Scatterer Interferometry (PSI). This technique offers the advantages of wide area coverage, high sensitivity to small deformations, and day and night and all-weather operation, which makes it suitable for man-made structural health monitoring. As far as bridge monitoring is concerned, the X-band images are the extensively used PSI data [7,10,11,12] This is mainly due to the high spatial resolution of X-band data, and their high sensitivity to displacements with respect to the C- and L-band. The spatial coverage of a single Sentinel-1 image (250 by 180 km) and their free availability suggest a great advantage with respect to X-band data in terms of costs
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