A Novel Framework for the Dynamic Characterization of Civil Structures Using 3D Terrestrial Laser Scanners

Despite the success of traditional structural health monitoring (SHM) techniques that rely on discrete sensors, several challenges still exist: (1) structures of interest need to be accessed for instrumentation, which is not always feasible due to complex site conditions; (2) the reliability of the results is highly dependent on the locations and the limited number of sensors mounted on the structure. To overcome these challenges, there is a critical need for non-contact monitoring techniques (e.g., laser scanners). While there has been substantial research conducted on the use of terrestrial laser scanners (TLS) (i.e., ground-based LiDAR) in monitoring the static deformation of civil structures, there have been only a few studies on the use of TLS in monitoring the dynamic vibrations of structures, which is critical information for SHM. Therefore, the main objective of this study is to develop a novel end-to-end framework to monitor the dynamic vibrations of structures using a TLS operating in the helical mode, where the TLS is operating at a fixed horizontal angle. To accomplish this goal, an extensive experimental study was conducted to investigate the effect of structure-based parameters on the robustness of TLS-based dynamic monitoring. The key parameter investigated in this chapter is the natural frequency of the specimen. A reconfigurable steel tower and weight plates were used to vary the dynamic structural parameters in this experiment. Accelerometers and infrared-based sensors were used in testing for the validation of TLS measurements. A novel spatio-temporal framework was developed to extract the dynamic vibrations of the structure of interest from the helical point clouds. The framework utilizes the density-based spatial clustering of applications with noise (DBSCAN) and change detection algorithms. The results show that the TLS can detect sub-millimeter structural vibrations. Furthermore, the dynamic response and characteristics extracted by the TLS framework closely match those of the accelerometers and infrared-based sensors. Hence, the results indicate the great potential of using TLS in monitoring the dynamic response of structures remotely.