The local buckling strength and behavior of slender tubular steel structures are sensitive to the nature and magnitude of initial geometric imperfections. The manufacturing process of such structures is known to introduce geometric imperfections into structural members. A new manufacturing process for spirally welded tapered tubes is based on an innovative process, where the tubes are rolled from flat steel plates and have two continuous, helical welds. Both rolling and welding are known sources of geometric imperfections, and the imperfections resulting from the tapered spiral welding process have not been studied. To address imperfections in design, existing non-computational design methods rely on conservative knockdown factors on the critical buckling stress. These knockdown factors are based on test data, few of which have been carried out on relatively slender specimens subjected to flexure and none of which have been carried out on tapered, spirally welded specimens. As such, these factors may not reflect the behavior of high slenderness, tapered specimens subjected to flexure and manufactured with spiral welding. For these reasons, large scale flexural tests were carried out on tapered spirally welded steel tubes to understand their behavior and buckling strength, including the effect of geometric imperfections. Laser scans of the manufactured tube geometry were completed before, during, and after each test. In light of existing design standards, all scan results are parameterized into common imperfection types. This allows characterization of the initial geometry as well as the evolution of these imperfections under flexural loading. The results are expected to enable finite element-based design methods and an evaluation of existing non-computational design methods for steel tubes.
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