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GATE 2018 CE (CE2) – Question 41

Concrete Structures · Design and detailing of beams and slabs · 2 marks · Multiple choice

A singly reinforced rectangular concrete beam is 300 mm wide with effective depth 400 mm, M25 concrete and Fe500 steel. For an under-reinforced beam, the maximum number of 16 mm reinforcing bars is ______.

  1. 3
  2. 4
  3. 5
  4. 6

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Correct answer: (C) 5

Explanation

For Fe500, $x_{u,\max}=0.46d=184$ mm. Equating limiting concrete and steel forces gives $A_{st,\lim}=0.36(25)(300)(184)/(0.87\times500)=1142.07$ mm². A 16 mm bar has area 201.06 mm², giving a limit of 5.68 bars. Choose the greatest smaller whole number: 5 (C).