Effective length corresponds to the distance between the points of inflection in the buckled mode. 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.
- In the Euler’s equation, the column ends are assumed to have pin (or hinged) connections. If the end conditions are different from pins (i.e. fixed, free, etc.) then the formula will not apply as such.
- To overcome this difficulty, the actual length of the column has to be modified by using a multiplying factor.
- The length, thus, obtained is called the ‘effective length’ of the column. The effective length of columns for various end conditions is given in Table below.
Note : (i) L is the unsupported length of compression member.
(ii) For battened struts the effective length shall be increased by 10 percent.
In calculation of the ‘slenderness ratio’, the value of l is taken as the ‘effective length’ of the column.
The maximum slenderness ratio as per recommendation of IS : 800 is 180 for loads resulting from dead and imposed loads. For wind and earthquake forces, this is allowed up to 250, provided the deformation of such members does not adversely affect the stress in any other part of the structure.