ETABS (O/S #52) column buckling.
Columns in ETABS will show O/S #52 when Dns exceed 1.4. Most engineers will solve the problem by increasing the column size or adding beams. In the following example will show how to avoid the problem without increasing the column size. The column dimensions are 700x1700mm with 44T32 reinforcement.
1- ETABS take the clear height of the floor without subtracting the floor thickness. As shown in Fig 1 the floor height is 8.29m while if you subtract slab thickness the clear height will be 7.88m. Just by assigning the right column height Dns will decrease from 1.727 to 1.555 as shown in Fig 2.
2- ETABS doesn’t consider the steel area in calculating (EI)eff, it will be calculated only from equation (6.6.4.4.4a) as shown in Fig 3. Taking steel area in consideration will increase (EI)eff which will increase Pc critical buckling load and increasing Pc will decrease Delta (6.6.4.5.2) Fig 4. As shown in Fig 5 using excel the Dns decrease to 1.285 which is less than 1.4
