Full-field geometric imperfection and effect on cross-section capacity of circular steel tubes

Measurements on the geometric imperfection of circular steel tubes used in building structures were limited to specific longitudinal lines of the outer surface in existing studies. This study is aimed at detecting full-field geometric imperfection of circular steel tubes and evaluating its influence on cross-section capacity. First, geometric imperfections of 71 specimens consisting of four common types (i.e., hot-rolled and cold-rolled carbon steel circular tubes, cold-drawn and cold-rolled stainless steel circular tubes) were measured using laser scanning techniques. Observations from 3D scanning models demonstrate that the dominant imperfections for seamless tubes (hot-rolled carbon and cold-drawn stainless steel circular tubes) are cross-section ellipticity and uneven thickness, while welded tubes (cold-rolled carbon and stainless steel circular tubes) are mostly influenced by cross-section ellipticity. Based on the measured geometric profile data, imperfection distribution modes of outer-surface and thickness were proposed separately, and then imported to finite element (FE) simulation. Parametric analysis was conducted to evaluate the influence of geometric imperfections on cross-section compression and bending capacity values. Totally, seven types of outer-surface and three types of thickness imperfection distribution modes were used. Simulation results indicate that considering geometric imperfections generates negligible influence on cross-section capacity for the circular steel tubes studied. Finally, the influence of mesh density on capacity prediction of circular steel tubes was discussed. This study illustrates the actual full-field geometric imperfection distribution of circular steel tubes and discusses its effect on cross-section capacity, which provides useful information for improving the efficiency and accuracy of FE analysis on circular steel tubes. •Full-field geometries of 71 circular steel tubes were measured using laser scanning.•Geometric imperfection modes were proposed for outer-surfaces and thickness.•Geometric imperfections have negligible influence on cross-section capacities.