Overturning collapse has been regarded as one of the most critical failure modes for single-column-pier bridges in current practices. To reveal the entire overturning process, a meticulous three-dimensional (3D) simulation of bridges with superstructures, bearings, and piers, considering geometric and material nonlinearities, was first established. Multiple load patterns were applied, including the practical eccentric truckloads that lead to overturning incidents and the conventional checking loads that are defined in the bridge design specifications. Second, four sequential limit stages of the overturning process were defined to precisely describe the structural behaviors under different mechanical conditions before the final collapse. A safety indicator was further proposed to quantify the possibility of overturning with respect to different limit stages. Using such a safety indicator in a case study, the ability of bridges to resist overturning was assessed and compared to results from the specifications and field observations. By doing this, the drawbacks of specifications in checking the safety of single-column-pier bridges were demonstrated. A parametric study was finally conducted to investigate the influence of different single-column-pier bridge arrangements on the overturning behaviors. It can be concluded that the specification-based methods greatly overrate the safety level of single-column-pier bridges, whereas the safety indicator provides more reasonable results as well as multiple-sublevel safety warnings up to the final collapse. Additional findings and suggestions for a better design or maintenance of single-column-pier bridges in curved-girder cases were also discussed.

This study applies structural dynamics monitoring to identify the presence of bridge scouring through tracing the changes of vibration characteristics induced by scour. Four scour-indicating dynamic features, i.e., the frequency change ratio, modal assurance criterion, mode shape curvature, and flexibility-based deflection, are applied as the scour indicators. Based upon the study of a cable-stayed bridge, each scour indicator is calculated and its corresponding relationship with scour depth is obtained. The feasibilities and effects of using each indicator ae comprehensively examined. After comparison, the flexibility-based deflection is finally recommended as a sensitive and practical indicator to identify the presence of the scouring. When applied in practice, the deflection can first be extracted from the ambient vibration measurement; then the scour depth can be back-deduced based on the preobtained relationship between the deflection and scour depth. For the specific cable-stayed bridge investigated in this study, the pylon-based deflection indicator can identify the scour presence more effectively and distinguishably. The scour location can also be known because the scoured pylon or pier shows many obvious deflection changes compared with those without scour effects. This study demonstrates that tracing the change of vibration responses can both qualitatively and quantitatively identify the scour of cable-stayed bridges. This vibration-based technique does not require any underwater devices or operations, which could be integrated into a routine assessment task for bridges.

In recent years, efforts have been devoted to utilizing terrestrial laser scanning for bridge spatial performance inspection, but they are still restricted to small or medium-span bridges, like some historical heritages. Due to the large-scale dimensional features of long-span bridges, applications of 3D point cloud techniques still remain challenging, such as the extra-long scan range and extreme-small incidence angle when scanning a bridge with a span over 1000 m. Moreover, rare attempts can be found for the performance evaluation of point cloud registration methods for long-span bridges as well, which is a critical basis for further spatial deformation recognition on the point cloud data. Hence, in this study, a cross-evaluation of three iterative closest point (ICP) registration methods is conducted for long-span suspension bridges, namely, traditional ICP, kd-tree-based ICP, and feature point-based ICP algorithms. We conducted field laser scanning on the Ma’anshan Yangtze Bridge, an 1880 m long suspension bridge located in China. The results show that the feature point-based ICP algorithm outperforms the other two in terms of convergence rate and execution time for a single iteration due to the smaller number of registration points compared to the other two algorithms. Moreover, it also gives more precise values in terms of bridge tower spatial deformation identification. Meanwhile, due to efficient data organization, the kd-tree-based ICP algorithm takes less time for a single iteration than the traditional ICP algorithm. Finally, two suggestions for algorithm improvement in terms of efficiency optimization and accuracy improvement of long-span bridge deformation analysis are proposed based on the assessment results.