Sugata Bhattacharya, PE

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FEM Analysis of Time Dependant Losses

• Sugata Bhattacharya, PE
• Head Civil Structural Deptt
• LT Engineering

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LT

• India largest private sector engineering and
  construction company (http//www.larsentoubro.com/
  investors/default.asp)
• Annual revenue exceeding 4 billion USD
• 22000 employees
• Services offered
• EPC Projects in Oil and other sectors
• Infrastructure projects
• Modular fabrication facilities

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Brief History

• Presented a paper in 1999 on FEM Analysis of
  Prestressed Box Girder
• Sample girder under construction -O
• Excel spread sheet for post processing of data -O
• Photograph of one segment during construction -O

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Time Dependent Losses

• Shrinkage
• Shrinkage strain 0.0002 / Log10 (t2)
• t Age of transfer in days
• For t 21 days
• Shrinkage strain 1.47 X 10-4
• Equivalent temperature increase in tendon
  1.47X10-4/11X10-6
• Creep
• Ultimate creep strain Coefficient x Elastic
  strain
• Coefficient is 1.6 at 28 days / 1.1 at 1 year

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Losses As Temperature Force

• Simplified Model 0
• Steps Creep loss
• Perform stiffness analysis for Dead Load and
  Prestressing load. Input file -0
• Determine net elongation of the tendon due to
  application of loads -gt Calculate net strain -gt
  Calculate creep strain. Determine equivalent
  temperature rise. Excel file -0
• GTS Input file -0

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Time Dependent Losses

• Steel relaxation
• At 1000 hours 0.025 X (e1 e2)
• e1 Strain in the tendon due to prestressing
  load
• e2 Strain in the tendon due to dead load
• As per Indian code the final relaxation loss
  value occurs after 0.5 X 106 hours and the value
  is 2.5 times the 1000 hour value

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Losses As Temperature Force

• Simplified Model 0
• Steps Relaxation loss
• Perform stiffness analysis for Dead Load and
  Prestressing load. Input file -0
• Determine net elongation of the tendon due to
  application of loads -gt Calculate loss of strain
  due to relaxation. Determine equivalent
  temperature rise. Excel file -0
• GTS Input file -0