Quiz: Civil Engineering 15 Jan 2020

Quiz: CIVIL ENGINEERING
Exam: NPCIL-SCIENTIFIC ASSISTANT (CIVIL)
Topic: STRENGTH OF MATERIALS

Each question carries 1 mark
Negative marking: No negative marking
Time: 10 Minutes

Q1. The load at the free end of a uniform cantilever beam is increased, the failure will occur
(a) At the middle
(b) At the fixed end
(c) At the point of application of load
(d) Anywhere in the span

Q2. Find the tensile stress of a mild steel rod of 18mm diameter. Given: ultimate load = 9.0 ton.
(a) 0.03 Ton/sq.mm
(b) 0.02 Ton/sq.mm
(c) 0.05 Ton/sq.mm
(d) 0.06 Ton/sq.mm

Q3. Shear span is defined as the zone where:
(a) Bending moment is zero
(b) Shear force is zero
(c) Shear force is constant
(d) Bending moment is constant

Q4. For a given elastic material, the elastic modules E is 210 GPa and its Poisson’s Ratio is 0.27. What is the approximate value of its modules of rigidity?
(a) 105 GPa
(b) 83 GPa
(c) 159 GPa
(d) 165 GPa

Q5. A solid metal bar of uniform diameter D and length L is hung vertically from a ceiling. If the density of the material of the bar is P and the modulus of elasticity is E, then the total elongation of the bar due to its own weight is
(a) PL/2E
(b) PL²/2E
(c) PE/2L
(d) PE/2L²

Q6. Maximum strain energy theory for the failure of a material at the elastic limit is known as
(a) Guest’s or Tresca’s theory
(b) St. Venant’s theory
(c) Rankine’s theory
(d) Haigh’s theory

Q7. If a load of 40 KN is applied in a compressive manner on a rod whose cross section is 10 mm ×20mm, then what will be the compressive stress on the rod in MPa?
(a) 0.2
(b) 2
(c) 20
(d) 200

Q8. A beam fixed at both ends carries a uniformly distributed load on entire length. The ratio of bending moment at the support to the bending moment at mid span is given by
(a) 0.5
(b) 1.0
(c) 1.5
(d) 2.0

Q9. The maximum dimension of a core section for a rectangular cross-section under eccentric loading on a column (b×d) is
(a) b/6
(b) d/6
(c) d/8
(d) b/3 and d/3

Q10. Which of the following statements is incorrect about Poisson’s ratio:
(a) can be negative
(b) can be zero
(c) can be positive
(d) can be Fractional value
Solutions

S1. Ans.(b)
Sol. If the load at the free end of a cantilever beam is increased the failure will occur at the fixed end because due to increase of load moment resisted by fixed support is increased and when support moment reaction increased beyond its limit then failure occur.

S2. Ans.(a)
Sol. Diameter = 18 mm
Ultimate load = 9.0 ton
Tensile stress = (9.0 ton)/(π/4×18²)
= 0.035 ton/mm²

S3. Ans.(c)
Sol. Shear span is the distance from the point of application of concentrated force to its respective reaction force. throughout shear span the shear force is constant.
“Shear span is defined as the zone where shear force is constant.”

S4. Ans.(b)
Sol. Given, Elastic modulus (E) = 210 GPa
Poison ratio (μ) = 0.27
Modulus of rigidity (G) = ?
E = 2G(1+μ)
G =E/2(1+μ)
=210/2(1+0.27)
▭(G=82.67 GPa≈83 GPa)

S5. Ans.(b)
Sol. The elongation of bar due to its own weight (w) is
∆=WL/2AE
Now W = PAL
∴ ∆ =PL²/2E

S6. Ans.(d)
Sol. → Maximum principal strain theory (St. Venant’s theory)
→ Maximum principal stress theory (Rankine’s theory)
→ Maximum strain energy theory (Bectami-Haigh’s Theory)
→ Maximum shear stress theory (Huber Hencky von-mises theory)

S7. Ans.(d)
Sol. Given,
P=40 kN=40×10^3 N
A=10×20 mm^2
σ= ?
σ=P/A
=(40×10^3)/(10×20)
▭(σ=200 MPa)

S8. Ans.(d)
Sol. A fixed beam carries UDL on entire length, then the bending movement
→ at supports =(WL^2)/12
→ at centre = (WL^2)/24
Hence ratio of bending moment at support to the bending moment at mid span is =
=((WL^2)/12)/((WL^2)/24)
=24/12
=2.0

S9. Ans.(d)
Sol. The maximum dimension of a core section for a rectangular cross-section under eccentric loading on a column (b × d) is b/3 or d/3. The shape of kern or core for rectangular and I – section is Rhombus.

S10. Ans.(a)
Sol. The Poisson’s ratio is a property of material which can not be negative.
▭(0≤μ≤0.5)
Poisson’s ratio in elastic range = 0.3
Poisson’s ratio in plastic range = 0.5

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