1. Post-Tensioning in Bridge Applications
Local Presence – Global Competence
1 AzSCE Bridge Technical Committee Presentation – December 8, 2009

2. Post-tensioning Overview
Bonded vs. Unbonded Post-tensioning
Internal Tendons vs. External Tendons
Strand Systems
Bar Systems
Applications
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3. Unbonded Post-Tensioning
Greased & PE Sheathed Strand Tendons
Ungrouted Bar Tendons
External Tendons (May be Grouted)
Stress Increases are Distributed Along Tendon
Length
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4. Bonded Post-Tensioning
Tendons Grouted Following Tensioning
Provides Corrosion Protection to PT Steel
Anchorage Redundancy Provided through
Bond Transfer
Stress Increases in PT Steel are Localized
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5. Typical Threadbar PT System Details
DYWIDAG Threadbar
• Minimum 150ksi Ultimate
• Conforms to ASTM A722
• Most Efficient with Shorter Tendon Lengths
• Anchor Losses ~0.035“ vs. 0.375“ for Strand
DYWIDAG Threadbar Anchorage System
• Conforms to AASHTO Normal Anchorage Definition
• Anchorage Acceptance by Calculation
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6. Threadbar PT System Specifications
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7. Typical Strand PT System Details
DYWIDAG MA Anchorage System
Use of 0.5“ or 0.6“ Strand
Capacity varies from 5-0.6“ to 37-0.6“
Special Anchorage Device per AASHTO
Approval through Proof Testing
ADOT Acceptance based upon Caltrans
Approval
Additional Local Zone Confinement by
Supplier
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8. DYWIDAG MA Anchorage System
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9. Duct Installation
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10. Strand Installation
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11. Stressing Operations
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12. Grouting Operations
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13. PT System Specifications
AASHTO
Stringent Anchorage Testing Requirements
Testing to 1.2GUTS
Additional Local Zone Reinforcement
State DOT
Generally Local Adaptations of AASHTO or Other States
May Accept Anchorage Systems on the Basis of Other State„s Prequalification
May Account for Regional Climate Conditions and Construction Practices
PTI – Post-Tensioning Institute
Bonded & Unbonded PT
Rock and Soil Anchors
Stay Cables
Specification for Grouting of Post-Tensioned Structures
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14. PT Grouting Specifications
Evolution of Grouting Practices
New Specifications originating with Florida DOT
Born from corrosion problems discovered in poorly grouted tendons.
Revises both material specifications and construction practices.
Certification of Personnel (ASBI / PTI)
Adopted in most eastern states, in progress in Nevada.
Prepackaged Grouts
Prequalification testing required.
Use of Colloidal Mixing Equipment.
Zero Bleed requirements.
Extensive production testing
Flow Cone, Wet Density (Mud Balance), Wick-induced Bleed, etc.
Permanent Grout Caps (SS or Reinforced Plastic)
Air Testing
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15. Typical PT Layout Details
Typical Simple-Span Widening
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16. Typical PT Layout Details
Typical Simple-Span Widening
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17. Common Design Issues
Areas where special detailing may be required:
Large Abutment Skew Angles
Shallow Structure Depths
Upper Bent Cap Reinforcement
Girder Clearance for Ducts
Small Radii Horizontal Curves
Hinges
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18. Common Design Issues
Large Abutment Skew Angles
Limited Abutment Diaphragm Thickness
Large Blockout Depths
Staggering of Blockouts at Sloped Exterior Girders
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19. Common Design Issues
Shallow Structure Depths
Adequate Depth to Fit All Anchorages
Joint Seal Blockout Clearance to Upper Anchorage Spiral
Staggering of Anchorages to Meet CGS at Abutments
Exposed Spiral at
Joint Seal Blockout
3ft. structure depth with 12” joint seal notch
required use of smaller, multiple anchorages to meet CGS.
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20. Common Design Issues
Bent Cap Reinforcement
Adequate Clearance for PT Ducts at High Points
Bundled Top Cap Reinforcement
Column Hoop Reinforcement
Ducts must clear below bundled main cap
reinforcement at high point.
Ducts must also be protected from
damage if exposed above construction
joint.
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21. Common Design Issues
Girder Clearance for Ducts
Clearance Above Soffit Reinf. at Low Points
Increased Horizontal Reinforcement Size = Reduced Duct Clearance
Web thickness increased near bents to provide duct clearance with #25 horiz. reinforcement.
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22. Common Design Issues
Hinges
Adequate Stressing Clearance between Frames
Vertical Clearance for Anchorages at Seat-end
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23. Common Design Issues
Horizontal Curvature
Ducts Tied to Outside of Curve
Duct Tie Reinforcement added for Horizontal Restraint
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24. Problem Areas
Anchor Zone Congestion
Importance of Concrete Consolidation
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25. Problem Areas
Voids resulting from poor consolidation of concrete near anchorages.
Complete removal of all loose concrete is
mandatory for repair to restore full anchorage
performance.
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26. Problem Areas
Where did my anchorages go?
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27. Problem Areas
They„re in here!
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28. Thank You
Contact us!
- Preliminary Design Concerns
- Unique Applications
- Specification Development
- Repair & Strengthening
DSI is available to help.
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29. Local Presence – Global Competence
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