A Terrestrial LiDAR-Based Detection of Shape Deformation for Maintenance of Bridge Structures

A terrestrial light detection and ranging (LiDAR) can be used to construct the building information modeling as well as to measure shape deformation that varies with time or load during or after construction. Thus, the measurement can be utilized for risk management and the completion inspection during and after construction, and for life cycling cost analysis to decide the reconstruction of existing structure. In this regard, this paper presents a practical feasibility study of a shape information model to monitor deformation or deflection of bridge structures with data loss minimization and computational efficiency. The 3D position information of the structure was obtained using terrestrial laser scanning, and the octree data structure was used for efficient processing of the acquired large-scale scan data. To accomplish this, we constructed a shape information model which means a 3D visualization process on the basis of the octree algorithm, which converts point cloud data via voxel to the improved octree structure by efficient management of empty nodes. First, laser scanning was carried out on a steel box-girder bridge (Bridge 1) and a steel I-girder bridge (Bridge 2), and the data for $35.4\times 29.2\times 6.89{\text{m}}^3$ and $9.3\times 5.4\times 1.8{\mathrm{m}}^3$ in each test-bed area were compressed from 158.72 to 13.05 MB with 91.7% reduction for the Bridge 1 and from 21.5 to 2.3 MB with 89.3% for the Bridge 2. As a next step, the shape information model was applied to the deflection estimation of another steel box girder bridge in service (Bridge 3) associated with the octree space division. The results showed the reasonable deflection values in comparison with the LVDT measurement. The proposed approach can provide useful information for effective condition evaluation and maintenance of bridge structures.