Background Essay: Columns: Finding the Strongest Shape

Columns are among the oldest and most effective building elements for resisting the pushing, or compression, that takes place in all kinds of structures. Paired with horizontal beams, these critical forms can carry the weight of an entire structure. Still, each column has its limits, and some types perform far better than others.

Columns can fail, or collapse, in two ways: by crushing and by buckling. Crushing results when the weight of a well-distributed load simply exceeds the compressive strength of the material from which the column is made. Because columns are usually constructed from dense materials such as stone, concrete, or steel, this type of failure is relatively uncommon.

Columns usually fail for reasons of instability, rather than lack of strength. Assuming that a column is attached to a solid foundation, stability is usually related to the column's dimensions. Shorter, thicker columns are far more stable than long, slender columns. Like short, thick horizontal beams, shorter, thicker columns are more resistant to bending than are slender columns, and a column that resists bending also resists buckling.

Shape also plays an important role in the stability of a column. The cylinder is one of the most widely used shapes in column construction. This is because its circular cross section places the column's material and its outer boundary at a consistent distance from the center, such that the column has no side that is weaker -- and thus more susceptible to buckling -- than any other.

Finally, proper placement of a load is critical to the stability of a column. The more closely a load is applied to the center of the top of a column, the more stable that column will be. As a load moves away from the center of a column, the side of column to which the load shifts takes on more and more of the load. Such an unbalanced load can cause a column to bend in the same way that an overloaded beam bends, and may lead to buckling.