A contractor is building a sturdy deck to overlook a beautif

A contractor is building a sturdy deck to overlook a beautiful wildlife park. The deck is to support several people, so that each column is designed for 100kN load. If the columns are mounted into concrete footings and bolted to deck at top as shown above, with L=3.25m and outer diameter, d=100mm, what must be the minimum wall thickness of each column to have a factor of safety of 3 on buckling?

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Solution

Solution :

For bolted & cemented in concrete, said column end conditions assumed to be fixed.

Assuming column to be Cast Iron Material (As Material for column is not mentioned here)

Now taking compressive stress for CI as 240 MPa

Factor of safety = 3

permissible stress = 80 Mpa

Induced stress = Force/Area

Force is 100 x 10^3 N

Area = pi/4 (d^2-di^2) d= outer dia

di = inner dia

80 N/mm^2 = 100 x 10^3/(pi/4 (d^2-di^2) )

pi/4 (d^2-di^2) = 100 x 10^3/(80)

pi/4 (d^2-di^2) =1250

100^2-di^2 = 1250x4/pi

100^2 -di^2 = 1591.54

di^2 = 10000-1591.54

di^2=8408.45

di=91.69mm

thickness = d-di

= 8.3 mm

Ans.Minimum thickness as per our assumtions should be 8.3mm