1.4.3. Columns

Columns:

• Vertical elements resisting axial compressive loads.

Columns are structural elements that stand vertically and support loads from above. Their primary role is to resist axial loads, which are forces that push or pull directly along the length of the column. This means that when a heavy weight, like a ceiling or roof, is placed on top, the column helps to bear that load down to the foundation.

Imagine a stack of books. When you place a heavy book on top of a stack, the book at the bottom (analogous to the column) has to support not only its own weight but also the weight of all the books above it. If the bottom book is strong enough, it will hold up the entire stack without collapsing.

• When subjected to both bending moments and axial load, they are referred to as “beam column.”

In some structures, columns are not just vertical supports; they also experience bending moments. This means that, in addition to supporting vertical loads, they may also have horizontal forces acting on them. When a column is tasked with handling both types of forces—bending and axial loads—it is often termed a 'beam column.' This combination is essential in various structures where the vertical element must also be designed to manage lateral forces, such as in earthquake-prone areas.

Think of holding up a large umbrella during windy weather. While you are keeping the umbrella upright (like a column supporting weight), you may also need to push against it to keep it from bending sideways (like the bending moment). Just as you have to balance these forces, engineers must ensure that beam columns can handle both vertical and horizontal forces.

• Susceptible to buckling which limits the strength of the member.

Columns, especially slender ones, can fail not just from the weight they carry but also from a phenomenon known as buckling. This happens when a column becomes too tall and thin, causing it to bend or 'buckle' under pressure rather than simply compressing. As the load increases, the tendency to buckle increases as well. This behavior limits the maximum load each column can safely support. Thus, in design, engineers must consider the height and thickness of columns to ensure they are stable and can safely carry the intended loads without buckling.

Imagine a tall, thin cardboard tube. If you push down on it from the top, it can collapse sideways rather than just squashing down. Now, if you were to use a wider tube with the same height, you would find that it resists that sideways collapse better. This is similar to how engineers design columns to maximize their strength and prevent buckling under heavy loads.

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