Building Construction Handbook, Eighth Edition

Buckling or Bending Effect † the previous example assumed total
rigidity and made no allowance for column length and attachments
such as floor beams.

The working stress unit for concrete may be taken as 0.8 times
the maximum working stress of concrete where the effective length
of column (see page 548) is less than 15 times its least lateral
dimension. Where this exceeds 15, a further factor for buckling can
be obtained from the following:

Using the example from the previous page, with a column effective
length of 9 metres and a modular ratio of 18:

Effective length...Least lateral dimension = 9000...300 = 30

From above table the buckling factor = 0„5

Concrete working stress = 5 N/mm^2

Equivalent combined area of concrete and steel = 111369 mm^2

Therefore: 5 ¾ 0„8¾ 0„5 ¾ 111369 = 222738 Newtons

222738
9 : 81

= 22705 kg or 22„7 tonnes permissible load

Effective length...Least lateral dimension Buckling factor

15 1„0

18 0„9

21 0„8

24 0„7

27 0„6

30 0„5

33 0„4

36 0„3

39 0„2

42 0„1

45 0

Simple Reinforced Concrete Column Design (2)