Structural Stability Theory and Practice

2Columns

2.1 General

Vertical straight members whose lengths are considerably greater than their lateral dimensions are usually called columns. These structural members are generally thought of as carrying axial compressive force, and are important load-carrying elements in a structure. An understanding of their behavior is therefore important for the overall safety of a structure. Columns can usually be classified as short, intermediate, and long, depending on the ratio of their length to the lateral dimensions and are defined by structural codes. A column can fail either due to material failure or because of lateral deflection called instability or buckling. Short columns fail due to material failure at a load that causes a yield point in a steel column, or crushing in a concrete column. In this failure, capacity of the column material to bear the load is exceeded. On the other hand, long columns reach a load that causes lateral deflection called buckling before the material capacity is reached. In long columns, buckling may occur when the material is still elastic in all fibers of the cross-section. When elastic stress of the material occurs before buckling takes place in the case of intermediate columns, this is called inelastic buckling.

The maximum axial load a column can support when it is on the verge of buckling is called the critical or buckling load. Though these two terms are used interchangeably, there is a difference between the two. The critical load is the load ...