Effective length of compression member

Effective length of compression member

Column or strut is a compression member, the effective length of which exceeds three times the least lateral dimension. For normal usage assuming idealized conditions, the effective length of in a given plane may be assessed on the basis of Table 28 of IS: 456-2000. Following terms are required.

Following are the end restraints:

•      Effectively held in position and restrained against rotation in both ends

•      Effectively held in position at both ends, restrained against rotation at one end

•      Effectively held in position at both ends, but not restrained against rotation

•      Effectively held in position and restrained against rotation at one end, and at the other restrained against rotation but not held in position

•      Effectively held in position and restrained against rotation in one end, and at the other partially restrained against rotation but not held in position

•      Effectively held in position at one end but not restrained against rotation, and at the other end restrained against rotation but not held in position

•      Effectively held in position and restrained against rotation at one end but not held in position nor restrained against rotation at the other end

Table.Effective length of compression member

Unsupported Length

The unsupported length, l, of a compression member shall be taken as the clear distance between end restraints (visible height of column). Exception to this is for flat slab construction, beam and slab construction, and columns restrained laterally by struts (Ref. IS:456-2000),

Slenderness Limits for Columns

The unsupported length between end restraints shall not exceed 60 times the least lateral dimension of a column.

If in any given plane, one end of a column is unrestrained, its unsupported length, l, shall not exceed 100b²/D, where b = width of that cross-section, and D= depth of the cross-section measured in the plane under consideration.