10- Best Introduction to Local Buckling-part-1

Last Updated on March 7, 2026 by Maged kamel

Introduction to Local Buckling-part-1.

We will start a new subject: local buckling of columns.

We have covered the subject of local buckling for beams, discussed the local buckling coefficient for both flanges and webs, and spoken about the general condition. There are three types: compact, noncompact, and slender sections.

This is a copy of Table 2-4 for the various types of ASTM specifications for different steel shapes, from which we can obtain the yield stress and Fult, the tensile stresses in KSI.

Classification of a compression member into stiffened and unstiffened parts.

In Local Buckling-Part 1, we will examine a cross-section of a column showing a bulged flange due to localized buckling. Also, there is another picture showing the flange, and the other part is for web buckling in the local buckling theory.

Any column consists of a series of intersection plates; one plate resembles the upper flange, the second plate is for the web, and the third plate is for the lower flange part.

The upper hatched part is on the right side, which is a part of the flange that is called an unstiffened element, the reason for that is because it is free on the edge but supported with the web on the other side.

In the Local Buckling-part-1, the flange is unlike the web, which is stiffened on both sides. That is why we have the definitions of stiffened and unstiffened for columns.

The site at the link, Chapter 6 – Buckling Concepts, Local Buckling, explains that general buckling applies to the whole column and to all beams.

The second picture shows the behavior of the stiffened plate under compression; because it is fixed on both sides, it deflects in the longitudinal direction. At the same time, for the unstiffened, it is warped in the longitudinal direction according to the Condition of the edges, whether hinged-free, free, or fixed. This is the picture link.

The third shape is for the unstiffened elements, for the wide flange I beam the unstiffened is shown with the white color at the left side, half of the bf flange, and with the thickness of t flange.

The second shape is for the c channel, for which the unstiffened section width is half of the flange width, and its thickness is the flange thickness, the third shape is for the t section, the unstiffened part is half of the flange width. The fourth shape is the same.

The vertical plate, web, can also be unstiffened since it is attached on one side to the upper flange and free from the bottom side. Also, the angle is an example of an unstiffened element.

Local buckling-part-1 stiffened parts of the steel column.

This is the picture link for the unstiffened elements for a clearer view.

For the shapes of the stiffened parts included in the web of W section, the section is fixed from the top flange and bottom flange,  the length is the height of the web minus the two kd values, where kd is the distance from the rounded part to the other rounded part,  and the thickness is the web thickness.

For the box section, two parts are considered stiffened, with different widths and lengths, marked in white. The W flange has a plate welded to the top flange; the plate can be regarded as a stiffened plate, the last shape for a box with two cells, for which the white mark indicates a stiffened part with width b from the right and left.

This is the picture view.

The PDF file for this post and the following post can be viewed and downloaded from the following link.

The next post is Number 10a-Easy study of Local Buckling-part-2.

For a good A Beginner’s Guide to the Steel Construction Manual, 14^th ed. Chapter 7 – Concentrically Loaded Compression Members.

For a good A Beginner’s Guide to the Steel Construction Manual, 15^th ed. Chapter 7 – Concentrically Loaded Compression Members.

For a good A Beginner’s Guide to the Steel Construction Manual, 16^th ed. Chapter 7 – Concentrically Loaded Compression Members.