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UPSC Civil Service Exam Questions - Engineering

Q1:

A simply supported beam of uniform cross-section is subjected to a maximum bending moment of 2.25 t.m. If it has rectangular cross-section with width 15 cm and depth 30 cm, then the maximum bending stress induced in the beam will be

A 50 kg/cm2

B 100 kg/cm2

C 150 kg/cm2

D 225 kg/cm2

ANS:B - 100 kg/cm2

We have the realtion,
σ = My / I ...........(1).

Where, Max Bending Stress = (Max Bending Moment * neutral axis) / Moment of Inertia,

Here, Max Bending Moment = 2.25 tm = 225000 kg cm,
Neutral Axis = 30/2 = 15 cm,
Moment of Inertia = (bh^3)/12= (15*30^3)/12= 33750 cm4.

Putting values in (1),
Maximum Bending Stress = 100 kg/cm2.