Elastic Compressive Strength of Aluminum Open Circular-Arc Sections

Currently, the Specification for Aluminum Structures (Aluminum Association 2010) indicates thin-walled open circular-arc plate sections with radii greater than eight inches have a lower elastic compressive strength than a flat plate with the same width and thickness. This seems inconsistent with intuition, which would suggest any degree of plate folding should increase the elastic buckling strength. This paper will provide an overview of a study recently completed by the authors on a wide range of curvatures—from a nearly flat plate to semicircular. To quantify the curvature, a single non-dimensional parameter is used to represent all combinations of circumferential width, thickness, and radius. Employing the finite strip method (CU-FSM), elastic local buckling stresses are investigated. Based on the ratio of critical stress values of curved plates compared to flat plates of the same size, equivalent plate-buckling coefficients are computed.  Using this data, nonlinear regression analyses are then performed to develop closed form capacity equations for five different edge support conditions. These expressions appear reasonable for calculating the elastic critical buckling stress for any open circular-arc section when the geometric properties (circumferential width, thickness, and radius) and the material properties (elastic modulus and Poisson’s ratio) are known. Examples that show the applicability of these equations to circular-arc geometries other than those used as a basis for their development are also provided.  

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