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GATE 2024 CE (CE1) – Question 30

Concrete Structures · Design and detailing of beams and slabs · 1 mark · Multiple select

Consider a balanced doubly-reinforced concrete section. If the material and other sectional properties remain unchanged, for which of the following cases will the section becomes under-reinforced?

  1. Area of tension reinforcement is increased.
  2. Area of compression reinforcement is increased.
  3. Area of tension reinforcement is decreased.
  4. Area of compression reinforcement is decreased.

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Show answer and explanation

Correct answer: (B) Area of compression reinforcement is increased.; (C) Area of tension reinforcement is decreased.

Explanation

A section is under-reinforced when the neutral axis is above the balanced position. Less tension steel means a smaller tensile force, so the neutral axis rises (C). More compression steel takes a larger share of the compression, so a smaller depth of concrete is needed and the neutral axis rises (B). The opposite changes (A and D) push the neutral axis down and make the section over-reinforced.