The effective width of a large rectangular chain pillar can be calculated by using either of the following formulae:

w_eff = (w₁ x w₂)^0.5
OR
w_eff = 4A/C

Where:
w₁ = width of one side of the chain pillar (metres)
w₂ = width of the other side of the chain pillar (metres)
A = Area of the pillar (metres²)
C = Circumference of the pillar (metres)
h = height of the pillar (metres)

The following restrictions have been placed on the above formulae

w₂ = 2w₁ or w₂, whichever is least,
If w₁/h <= 5, w₂ = w₁,
If w₁/h > 5 and w₂ > 2w₁, w₂ = 2w₁

Worked Example

Calculate the effective width of rectangular pillars of the following dimensions:

4 m high, 18 m wide and 36 m long.
3 m high, 18 m wide and 80 m long.

Solution

1.

w₁/h <= 5
Therefore, Use w_eff = w₁ = 18 m

2.

w₁/h > 5
w₂ > 2w₁
Therefore, set w₂ = 2w₁ = 36 m

Option 1
w_eff = (w₁ x w₂)^1/2
= (18 x 36)^1/2
= 25.5 m

Option 2
w_eff = 4A/C
= 4 x (18 x 36)/(18 +18 + 36+ 36)
= 4 x (648/108)
= 24 m