A concrete beam is post-tensioned by a cable carrying an initial stress of 1000 N/mm2. The slip at the jacking end was observed to be 5 mm. The modulus of elasticity of steel is 210 kN/mm2. What is the percentage loss of stress due to anchorage slip if the length of the beam is 30 m ?

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UPSC ESE Prelims (Civil) 20 Feb 2022 Official
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  1. 3.5%
  2. 35%
  3. 0.35%
  4. 30.5%

Answer (Detailed Solution Below)

Option 1 : 3.5%
Free
ST 1: UPSC ESE (IES) Civil - Building Materials
20 Qs. 40 Marks 24 Mins

Detailed Solution

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Concepts:

Loss in pre-stress = Strain due to anchorage × Modulus of elasticity of steel

Calculation

Given

Anchorage slip = 5 mm; Beam length = 30 m; Modulus of Elasticity of steel = 2.1 × 105 N/mm2,

Initial pre-stress = 1000 N/mm2

Loss of pre- stress = 1.67 × 10-4 × 2.1 × 105 =35.07 MPa

Loss in pre-stress = 3.51 %

 

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