Development of a Laser-Based Geometric Imperfection Measurement Platform with Application to Cold-Formed Steel Construction

Geometric imperfections play an important role in the strength and behavior of thinwalled metal parts such as those commonly used in cold-formed steel construction. The objective of this paper is to detail a newly developed imperfection measurement platform, where the full-three dimensional (3D) imperfect geometry of a cold-formed steel member can be measured and reconstructed with reasonably high throughput and sufficient accuracy to explore all relevant imperfections. The measurement platform is composed of a two-dimensional laser sensor mounted on rotary and linear stages. Specimens are placed within a rotary ring and along a reference beam. The linear stage provides a means to scan the length of the specimen and the rotary stage a means to scan from any angle. Control of the custom linear and rotary stages are detailed in the paper, and corresponding control accuracies are studied. A procedure for registering the individual scans into the complete 3D model reconstruction (point cloud) is provided by specific calibration tests, from which rotation and translation quantities can be found to transform surfaces measured in local coordinates to a universal global coordinate system. A variety of different imperfection quantities, from basic dimensions and out-of-plane deviations to more advanced spectral and modalbased imperfection magnitudes may be rapidly processed from the 3D model. Accurate understanding of geometric imperfections is critical to the long-term success of analysis-based design paradigms for cold-formed steel constructions. The apparatus detailed herein will be used to provide a broad suite of imperfection information to assist in these new efforts.