A member which carries an axial compression is known as a compression member. It is also called a strut. A compression member may be called – short or long depending on the slenderness ratio (KL/r), where KL is the effective length and r is the least radius of gyration of the cross section. For small values of KL/r, a compression member undergoes only simple compression (Figure 4.1(a)). Such a compression member is known as a short column. For large values of KL/r, a compression member undergoes buckling i.e., side way deflection (Figure 4.1(b)). Such a compression member is known as a long column.