**Introduction**

Column is the vertical structural element used to support the load of the building. It is widely used in architecture from the freedom it provides to distribute spaces while complying with the function of supporting the weight of the construction; is a key element in the scheme of a structure and the proper selection of size, shape, spacing and composition influence directly in its capacity.

For the column the defining characteristics and behavior to define the aspects to be taken into account in the design of the columns of wood, steel and reinforced concrete indicated; additionally one example for each type of material is included.

**Definition**

The column is subjected mainly to compression element, therefore the design is based on the internal force, together due to the particular column conditions, also designed to flex so that the combination thus generated is called flexocompresión.

According to the current use of the column as part of a portico, is not necessarily a vertical straight element, but is the element where compression is the main factor that determines the behavior of the element. That is why the column predimensioning is to determine the dimensions that are able to withstand the compression applied on the bending element and on the design due to various factors1. Note that the resistance of the column decreases due to geometry effects, which influence the fault type.

The geometric effect of the column are called esbeltez2y is an important factor, since the form depends on the slenderness fail to little slender column crush failure and this is called short column type plus long column element called esbeltosse and failure is buckling. The intermediate column is where the fault is a combination of crushing and buckling. In addition, bending moments that are part of the design of the column decrease resistance element type column (Galambos, Lin and Johnston, 1999; Singer and Pytel, 1982).

**Behavior**

Among the fundamental requirements of a structure or structural element are: balance, endurance, functionality and stability. In a column can reach an unstable condition before reaching the maximum deformation or maximum effort. The instability phenomenon refers to buckling, which is a deflection occurring in the column (see Figure 3); appears when applied increases the bending moment on the element, the increase in the magnitude of deflection enlarges bending moment, thus increasing the curvature of the spine until failure; This case is considered unstable. Thus the column strength in compression has two limits, the resistance to short columns and stability for long columns (Figure 1). Thus stability parameter defining the new addition to the resistance and stiffness, the column dimensions (Beer and Johnston 1993; Popov, 1996; Timoshenko and Young, 2000).