Design of Compression Members | Design of Steel Structures we

DESIGN OFCOMPRESSION MEMBERS

1. Determine slenderness ratio of the member. If end conditions can be assessed, refer Table 11 in IS

code to get effective length. In case of bolted, riveted or welded trusses effective length shall be

taken as 0.7 L to 1.0 L where L is the actual length, depending upon the degree of end restraint

provided.

2. Various shapes of cross section are divided into buckling classes a, b, c and d for which Table 10

in IS 800–2007 may be referred.

3. Find imperfection factor a which is 0.21, 0.34, 0.49 and 0.76 for buckling class a, b, c and d

respectively.

4. Then, design compressive stress fcd of axial loaded column is given by

fcd =

where a = 0.5 [1 + a (l – 0.2) + l

]

and l = non-dimensional effective slanderners ratio

KL = Effective length

5. One can refer to Table No. 9 in IS 800–2007 also and use fcd straightaway.

Design of Laced Columns

1. Lacing may be single or double.

2. Thickness of flats for lacing shall not be less than of its effective length for single lacing and

of the effective length for double lacing.

3. Lacing bars shall be at 40° to 70° to the axis of column.

4. The distance between the two members should be such that ryy

> rxx

5. Lacing shall be designed to resist shear Vt = 2.5 % of axial load in columns.

6. Effective length of laced column shall be taken as 1.05 times the actual maximum slenderness ratio.

7. Effective length of single laced column = L and that of double laced column = 0.7 L, where L is

actual length.

8. The slenderness ratio of lacing bars should not exceed 145.

Design of Battened Column

1. The number of battens should be such that the member is divided into not less than three bays.

2. ryy should be more than rxx

3. Effective slenderness ratio = 1.1 × Actual slenderness ratio.

4. Battens shall be designed to carry moments and shear forces arising from transverse shear force Vt

= 2.5% of axial load.

5. The effective depth of end battens shall not be less than the distance between the centroids of main

members.

6. The effective depth of intermediate battens shall not be less than 3/4 th of the above distance.

7. Thickness of battens shall not be less than of the distance between the innermost connecting

lines of rivets/bolts/welds

Design of Compression Members | Design of Steel Structures