Columns and struts are structural members subjected to compressive stresses primarily. When the member is vertical, it is called a column and when inclined it is called as a strut.
The members of a truss, which carry compressive loads, are called struts. The vertical members of a framed structure which carry compressive loads are called columns are divided into two major groups as short columns and long columns.
When the length of the column is not large as compared to its transverse dimensions it is called a short column. Short columns does not buckle. When subjected to loading. The design of short column is done for maximum permissible compressive stress.
When the length of the column is quite large as compared to its transverse dimensions, it’s a long column.
Long columns fails mainly by buckling.
[The columns may be treated as short columns if the ratio of effective length of the column to its least lateral dimension is ≤ 12 otherwise the columns may be treated as long]
And it > 12 long Column
If the load on the column is gradually increased to crushing load the stress in the column increases to crushing stress F C of the material of the column.
By dividing the crushing load by a suitable factor of safety the safe load on the column can be determined.
Load carrying capacity of Long columns: (Based on Euler‟s theory)
The load carrying capacity of a long column depends on the following factors.
1) Effective length of the Column.
2) Material of the Column.
3) Area of C.S of Column.
4) Moment of Inertia and shape of the Column.
Assumptions in Euler’s theory for load carrying capacity of long columns.
1) The material of the column is homogeneous.
2) The columns are initially straight with uniform C.C. subjected to perfectly axial dimensions.
3) The columns are long compared to lateral dimensions.
4) The load on the column is with in elastic limit.
5) The decrease in length of the column due to direct compression is neglected.
The load carrying capacity of long columns is given by Euler’s Crippling load (Or buckling load) as
Based upon the end conditions, the columns are divided into four groups
“Effective length” of a given column with given end conditions is defined as the length of an equivalent column of the same material and section with hinged ends having the value of „buckling load‟ equal to that of the given column.
Q) What is meant by the term critical load for a column? Write down the expression of Euler‟s critical load for (a) Both ends hinged (b) Both ends fixed.
The Euler‟s Critical load is the maximum load, which a column can resist at which the column buckles or has lateral deflections. It may be defined as the value of minimum compressive load at which the column buckles.