When the flat-width-thickness ratio (w/ t) exceeds about 30 for an unstiffened element and about 250 for a stiffened element, noticeable buckling of the element may develop at relatively low stresses. Present practice is to permit buckles to develop in the sheet and to take advantage of what is known as post-buckling strength of the section. The effective-width formulas, Eqs. (8.5) to (8.7), are based on this practice. To avoid intolerable deformations, however, w/ t, disregarding intermediate stiffeners and based on the actual thickness t of the element, should not exceed the following:
Stiffened compression element having one longitudinal edge connected to 60 a web or flange, the other to a simple lip
Stiffened compression element with both longitudinal edges connected to 500 a web or flange element, such as in a hat, U, or box-type section
Unstiffened compression element 60
