Local Buckling of I-Shape Members Bent About Their Weak Axis

Steel design standards in North America and Europe provide plate slenderness limits for the web and flanges to prevent local buckling of I-shapes before they attain the desired stress level. While significant research has been conducted on local buckling of I-shapes under strong axis bending, very little has been done on local buckling of I-shapes when they bend about their weak axis with the action of a superimposed axial force. Beam bending about weak axis is common in many framed structures. In the current editions of ANSI/AISC 360-16 and CSA S16-14, slenderness limits are provided to check local buckling of I-shapes when subjected to weak axis bending. One important difference between AISC and CSA local buckling requirements for I-shapes is that while, for any certain compactness, AISC recommends same slenderness limits of for both strong and weak axis bending, in Canadian standard, for class 3 section, flange slenderness requirements are different between strong and weak axis bending. The slenderness limits for weak axis bending in S16 have never been assessed experimentally or numerically. Strain distribution in I-shapes when bent about the strong-axis is significantly different from the strain distribution when bent about weak axis. Thus, the use of same slenderness limits for both strong-axis and weak-axis bending conditions is questionable, and should be investigated. This paper evaluates the slenderness limits in the current North American design standards for local buckling of I-shapes bent about the minor axis, with and without axial load. A nonlinear finite element (FE) model is developed using the commercial finite element software ABAQUS. A series of FE analysis considering various parameters such as web slenderness ratio (h /w), flange slenderness ratio (b /2t) is conducted to evaluate the current slenderness limits.

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