As we all know, the column’s primary function is to transfer the load from the beam to the foundation.
Here we are going to discuss the effective length. What is it? and how it differs for different types of columns.
What is the length of the column?
The column’s length is the distance between the two floors or the distance between the column’s fixed points (fixed or pinned), where all its movement is constrained in all directions.
What is effective length of column?
The column’s length where deflection occurs due to the bending moment by the supporting load is known as the effective length of the column.
The bending moment occurs on the column due to the compression load. The load which makes the column to bend is known as buckling load.
Why does buckling occur on the column?
A column that loses its stability when axially loaded is known to be buckled. That means it is going to be unstable.
Assume holding a wooden stick in your hand; now put pressure on the top. You will notice a small deflection in the middle of the stick. The deflection where it occurs is known as an effective length.
Now gradually increase the pressure. The stick tries to free themselves from your hand. That is known as buckling.
If a column is axially loaded, it will lose its stability and eventually go to fail.
Effective length of column for different end conditions
The different effective length of column is shown below pictures as per the column different bending moment.
K mentions the coefficient of effective length of column.
The theoretical & recommend effective length for column design purposes has been listed below as per the IS code 456. The structural engineer will calculate the effective length while designing the column to avoid the buckle happening.
|Column Support Conditions||Theoretical Value of Effective Length||Recommended Value of Effective Length|
|Column Fixed at Both Ends||0.5 L||0.65 L|
|Column Fixed at One End Hinged at another end||0.7 L||0.8 L|
|Both End Hinged||1 L||1 L|
|Fixed at one end & free at another end||2 L||2 L|
Happy Learning 🙂