Geometric Imperfection Measurements of Cold-Formed Steel Members Using a Portable Non-Contact 3D Laser Scanner

Thin-walled structures, including cold-formed steel framing, are sensitive to and affected by geometric imperfections. Characterizing imperfections is crucial for the design and analysis of thin-walled structures. Traditionally, 3D laser scans of members are conducted in a stationary rig prior to testing in the lab to characterize the initial imperfections. A new portable handheld 3D laser scanner capable of measuring metallic surfaces is now available for use and is evaluated for its accuracy at measuring geometric imperfections of cold-formed steel specimens. The portable scanner has the capability of measuring the detailed displacement field of a member under load while being tested, which was not previously possible in traditional stationary imperfection rigs. Advanced high-strength cold-formed steel (AHSS) is prevalent in the automobile industry but is currently being investigated for its use in the construction industry. As a result of its high yield strength, traditional cold-formed steel cross-sections will have higher slenderness, which may result in buckling mode interactions not typically seen in conventional steel sections. A series of lipped channel and zee sections were roll-formed from 0.6-mm thick grade 690 MPa AHSS sheets. Initial imperfections were measured, as well as the deformed shape of the members under load. The resulting 3D point cloud was analyzed to determine and categorize initial imperfections as well as the participation of local, distortional, and global buckling modes while under load. The measurements were compared to predictions of buckling mode participation from finite strip analyses in CUFSM as well as member displacements in shell-element finite element models.

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