Abstract
As far as we discuss the lateral buckling problems of I-shaped beams under the axial force and the end couples in plan of the web, we can easily understand the buckling behaviour by looking at it as column buckling of compression flange in the weak direction. First, the equilibrium equations of the lateral buckling are derived in terms of the lateral deformation of each flange of I-shaped beams. The approximate buckling stress for doubly symmetric I-shaped beams is obtained with measuring rule of the adequate slenderness ratio of compression flange of beams. And then, as a result of substituting the actual value about some I-shaped beams including wide flange sections and plate girders, it's made clear that the resultant equation closely approximates the exact solution. The lateral buckling problems of I-shaped beams with unequal flanges are also analyzed, and similar results are obtained. Finally, on the basis of these results the author makes clear design formulas for bending I-shaped beams and plate girders, and discusses these results comparing with the design formulas of A. I. J. Specification.
