Bending Theory

JKSSB Junior Engineer (Civil) · Mechanics and Structural Analysis · 14 practice questions with answers and explanations: 7 Easy, 6 Medium, 1 Hard.

Sample questions

Sample Easy question 1

The shear centre of a section is the point:

  1. At the top of the section
  2. At the centroid of every section
  3. Where the bending stress is zero
  4. Through which the load must act to bend the beam without twisting it
Show answer

Answer: D. For a channel section it lies outside the section, on the side of the web away from the flanges.

Sample Easy question 2

The moment of inertia of a rectangle of width b and depth d about its centroidal axis parallel to b is:

  1. bd³ ÷ 3
  2. bd³ ÷ 36
  3. bd³ ÷ 12
  4. db³ ÷ 12
Show answer

Answer: C. I = bd³ ÷ 12. The value bd³ ÷ 3 is about the base.

Sample Easy question 3

The section modulus of a rectangular section of width b and depth d is:

  1. bd² ÷ 12
  2. bd² ÷ 6
  3. bd³ ÷ 12
  4. bd² ÷ 3
Show answer

Answer: B. Z = I ÷ (d ÷ 2) = bd² ÷ 6.

Sample Medium question 4

The average shear stress in a solid circular section is 3 N/mm². The maximum shear stress, at the neutral axis, is:

  1. 4.5 N/mm²
  2. 3 N/mm²
  3. 6 N/mm²
  4. 4 N/mm²
Show answer

Answer: D. For a circle the maximum is 4/3 of the average.

Sample Medium question 5

A rectangular beam of 150 mm × 250 mm has an allowable bending stress of 10 N/mm². The moment of resistance is:

  1. 7.8 kN·m
  2. 31.2 kN·m
  3. 15.6 kN·m
  4. 11.7 kN·m
Show answer

Answer: C. Z = 150 × 250² ÷ 6 = 1.562 × 10⁶ mm³, and M = σ Z = 15.6 kN·m.

Sample Medium question 6

The moment of inertia of a rectangle 100 mm wide and 200 mm deep about its base is:

  1. 5.333 × 10⁸ mm⁴
  2. 0.222 × 10⁸ mm⁴
  3. 2.667 × 10⁸ mm⁴
  4. 0.667 × 10⁸ mm⁴
Show answer

Answer: C. By the parallel axis theorem, I = I_G + A h² = 6.67 × 10⁷ + 20,000 × 100² = 2.67 × 10⁸ mm⁴.

Sample Hard question 7

A beam section with I = 8 × 10⁷ mm⁴ carries a bending moment of 30 kN·m. The bending stress at 200 mm from the neutral axis is:

  1. 150 N/mm²
  2. 75 N/mm²
  3. 37.5 N/mm²
  4. 7.5 N/mm²
Show answer

Answer: B. σ = M y ÷ I = 30 × 10⁶ × 200 ÷ (8 × 10⁷) = 75 N/mm².

More Mechanics and Structural Analysis topics for JKSSB Junior Engineer (Civil)