STUDY ON BUCKLING OF SQUARE TUBES UNDER BENDING LOADS

Buckling behavior of square tubes under bending load depends on the direction of the bending moment. This paper deals with two directions. The first has an axis that crosses the side of a cross-section at right angles; the second has an axis that crosses the diagonal of a cross-section at right angles. Four-point bending tests are conducted at room temperature and at 300-degrees-C, using square tubes of three thicknesses (2.0, 2.5, and 3.0 mm), but having the same inside width (115 mm, excluding corner radius) and length (4000 mm). Local deformations and ultimate bending loads are measured. An empirical formula of the relationship between buckling wave growth and bending load is obtained by analogy with an equation derived from the results of bending theory for plates with an initial curvature. An empirical formula of the ultimate bending moment is also obtained by applying to square tubes Karman's effective width theorem for critical loads in plates. These formulae are proved to accurately represent the behavior of test and analysis values.