Equivalent and effective Lengths of Columns

The effective column length can be defined as the length of an equivalent pin-ended column having the same load-carrying capacity as the member under consideration.The smaller the effective length of a particular column,the smaller its danger of lateral buckling and the greater its load carrying capacity. It must be recognized that column ends in practice are neither perfectly fixed nor perfectly hinged. The designer may have to interpolate between the theoretical values given, to obtain a sensible approximation to actual restraint conditions.
 

Equivalent Lengths of Columns for Various End Conditions

S.No. Type Effective Length of member I
1. Effectively held in position and restrained in direction at both ends. 0.67L
2. Effectively held in position at both ends and restrained in direction at one end. 0.85L
3. Effectively held in position at both ends but not restrained in direction L
4. Effectively held in position and restrained in direction at one end and at the other end effectively restrained in direction but not held in position L
5. Effectively held in position and restrained in direction at one end and at the other end partially restrained in direction but not held in position. 1.5L
6. Effectively held in position and restrained in direction at one end but not held in position or restrained in direction at the other end. 2.0L

 

Note : L is the actual length of the member measured between the centres of effective lateral supports.

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