Point Cloud Processing for Damage Characterization of Steel I-Sections

When structural members experience impact damage, understanding their geometry is a critical step for assessing damage severity and determining how to maintain functionality and structural safety. Traditional methods for characterizing damage severity require hand measurements of displacement at discrete points along the member length. Terrestrial laser scanning (TLS) offers several advantages over manual measurements, such as more comprehensive data, improved accuracy, reduced need for lane closures, and avoiding work at height. However, TLS point cloud data are unstructured and must be processed to extract displacements. Existing methods for point cloud displacement measurements rely on manual techniques, where a point cloud is carefully manipulated to select individual points, but these approaches are impractical for obtaining a global member displacement curve. This paper presents a new semiautomated modular procedure for processing laser scan point cloud data of steel I-sections to obtain bottom-flange displacement curves along the length of a span. Several existing point cloud processing techniques are incorporated, including outlier removal, voxelization, cross-sectional slicing, and random sample consensus (RANSAC) regression. The proposed procedure measures horizontal and vertical displacements at three cross-sectional locations—the left corner, centerline, and right corner of the bottom-flange surface—so that the flange displacement and tilt can be accurately characterized. A person who has been trained can capture hundreds of measurements along a member length in less than an hour of postprocessing time, whereas existing methods would likely require several workdays to produce the same number of measurements. The procedure was developed using TLS data from steel I-girders damaged in overheight vehicle strikes on highway bridges. Laser scan data from a damaged steel-girder highway bridge in Mt. Vernon, Illinois, are used as a case study, and results from three other steel-girder highway bridges are also presented. The measurement procedure has been designed for implementation in structural engineering practice.