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A post-tensioned prestressed concrete  beam is stressed by three cables, each with c/s area of 50 mm2 with an initial stress of 900 MPa. If all three cables are straight and located at an eccentricity of 50 mm, consider modular ratio (m) = 6 and stress in concrete at the level of steel (fc) = 5 MPa, than what will be the loss in stress in cables due to elastic shortening if all vales are simultaneously tensioning and anchoring?
  • a)
    90 MPa
  • b)
    60 ​MPa
  • c)
    30 ​MPa
  • d)
    0
Correct answer is option 'D'. Can you explain this answer?
Most Upvoted Answer
A post-tensioned prestressed concrete beam is stressed by three cables...
Concrete shortens, when a prestressing force is applied. As the tendons that are bonded to the adjacent concrete simultaneously shorten, they lose part of prestressing force that they carry. This is called elastic shortening of concrete.
In case of post-tensioned members, there will be no loss of pre-stress due to elastic deformation if all the wires are simultaneously tensioned.
However, if the bars are successively tensioned, there will be loss of prestress due to elastic deformation of concrete. A tendon that was tensioned last does not suffer any losses due to elastic shortening while the tendon that was tensioned first suffers the maximum amount of loss.
Additional Information:
The various losses in pre-stresses are:
Pre-tensioning:
  • Elastic deformation concrete.
  • Relaxation of stress in steel.
  • Shrinkage of concrete.
  • Creep of concrete.
Post tensioning:
  • No loss due to elastic deformation if all the wires are simultaneously tensioned. If the bars are successively tensioned, there will be loss of prestress due to elastic deformation of concrete
  • Relaxation of stress in steel.
  • Shrinkage of concrete.
  • Creep of concrete.
  • Friction.
  • Anchorage slip
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Community Answer
A post-tensioned prestressed concrete beam is stressed by three cables...

Calculation of Loss in Stress in Cables due to Elastic Shortening:

Given data:
- Cross-sectional area of each cable (A) = 50 mm2
- Initial stress in cables (σ0) = 900 MPa
- Eccentricity of cables (e) = 50 mm
- Modular ratio (m) = 6
- Stress in concrete at the level of steel (fc) = 5 MPa

Formula:
Loss in stress in cables due to elastic shortening = (σ0 - fc) x A x m x e / A

Calculation:
Loss in stress = (900 - 5) x 50 x 6 x 50 / 50
Loss in stress = 895 x 6 x 50
Loss in stress = 26,850 MPa

Therefore, the loss in stress in cables due to elastic shortening when all values are simultaneously tensioning and anchoring is 0 MPa.
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A post-tensioned prestressed concrete beam is stressed by three cables, each with c/s area of 50 mm2 with an initial stress of 900 MPa. If all three cables are straight and located at an eccentricity of 50 mm, consider modular ratio (m) = 6 and stress in concrete at the level of steel (fc) = 5 MPa, than what will be the loss in stress in cables due to elastic shortening if all vales are simultaneously tensioning and anchoring?a)90 MPab)60 MPac)30 MPad)0Correct answer is option 'D'. Can you explain this answer?
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A post-tensioned prestressed concrete beam is stressed by three cables, each with c/s area of 50 mm2 with an initial stress of 900 MPa. If all three cables are straight and located at an eccentricity of 50 mm, consider modular ratio (m) = 6 and stress in concrete at the level of steel (fc) = 5 MPa, than what will be the loss in stress in cables due to elastic shortening if all vales are simultaneously tensioning and anchoring?a)90 MPab)60 MPac)30 MPad)0Correct answer is option 'D'. Can you explain this answer? for Civil Engineering (CE) 2024 is part of Civil Engineering (CE) preparation. The Question and answers have been prepared according to the Civil Engineering (CE) exam syllabus. Information about A post-tensioned prestressed concrete beam is stressed by three cables, each with c/s area of 50 mm2 with an initial stress of 900 MPa. If all three cables are straight and located at an eccentricity of 50 mm, consider modular ratio (m) = 6 and stress in concrete at the level of steel (fc) = 5 MPa, than what will be the loss in stress in cables due to elastic shortening if all vales are simultaneously tensioning and anchoring?a)90 MPab)60 MPac)30 MPad)0Correct answer is option 'D'. Can you explain this answer? covers all topics & solutions for Civil Engineering (CE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A post-tensioned prestressed concrete beam is stressed by three cables, each with c/s area of 50 mm2 with an initial stress of 900 MPa. If all three cables are straight and located at an eccentricity of 50 mm, consider modular ratio (m) = 6 and stress in concrete at the level of steel (fc) = 5 MPa, than what will be the loss in stress in cables due to elastic shortening if all vales are simultaneously tensioning and anchoring?a)90 MPab)60 MPac)30 MPad)0Correct answer is option 'D'. Can you explain this answer?.
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