Eccentrically Loaded Columns

Column

In structural engineering, column is a vertical structural element which transmits the weight of the structure above to the structural elements below through compression. The column is designed to resist the lateral forces, for the purpose of wind or earthquake engineering.  Because of the stress condition, other compression members are also said to be columns. It is used to support the beam in which the upper part of the wall or ceiling gets supported. In olden days, columns were constructed of stone some columns were made out of single piece of stone by turning on a lathe machine. Normally, single piece columns are among the heaviest stone that are used in architecture. At present the columns are constructed out of steel, precast concrete, or brick, and then it will be clad in an architectural covering or left uncovered. We will discuss about the eccentrically loaded columns.

Eccentrically loaded columns

There are two types of columns loading; they are, axial and eccentric. Either by buckling or crushing axially loaded columns may fail. Normally eccentrically loaded columns will fail by bucking. The eccentric load is one that is applied away from the centroidal axis of the cross section of the columns. Such load will apply bending in addition to the columns action that is resulting in deflecting shape. Normally it can be seen that one side of the column receives more compression than the other. The column cross section will be having the compressive stresses, as long as the applied load remains within the middle third of the section. While the applied load moves out of the core, tensile stresses are introduced. As the eccentricity increases, the extent of the bending moment that the section must also increases. The infinite eccentricity is an extreme case, resulting in the pure bending moment stress prism. For the sizing of the column, the awareness of the magnitude and distribution of the internal stress is very much important. In case of steel or wood column the small amount of the tensile stress has little effect, but it is very problematic if the column is of concrete or masonry.

Stress in eccentrically loaded columns

If an eccentrically loaded column is stressed beyond the proportional limit, then the stress strain relation varies from one point to other in the member in a complex manner. The accurate analysis is extremely difficult in it, but the approximate solution can be possible, but it based on two assumptions:

• The column axis deflect in a half sine wave, and
• The stress varies linearly across the section.

Questions:

• What is column?
• What is eccentrically loaded column?