Long-term displacement measurement of bridges using a LiDAR system

Long-term displacement measurements provide important information about the structural safety of civil engineering structures and the associated maintenance necessary. Most approaches developed for measuring displacement, such as direct measurements using the linear variable differential transformer and computer vision-based sensing, relate to campaign-type sensor deployment. However, these methods have critical limitations when used to accurately measure long-term displacement, because it is difficult in practice to appropriately handle unavoidable sensor movement. This study therefore proposes a long-term displacement measurement method using light detection and ranging (LiDAR) that is designed for use with short- and medium-span bridge structures. Reflectors that have higher reflectance than common construction materials (such as concrete and steel) are used to enhance measurement accuracy and reduce scanning time. Strategically deployed reflectors provide a reference point, which is independent of the LiDAR position. Thus, LiDAR can be temporarily installed in the field only when measurements are necessary. Expensive LiDAR systems can be employed to measure the long-term displacement of multiple bridges cost-effectively because permanent installation is not required. The proposed method is validated within the laboratory by focusing on LiDAR position independence and is then used during the early erection stages of a railroad bridge to measure long-term displacement