C:\fakepath\dsi bridge pt presentation
- 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 2
- 3. Unbonded Post-Tensioning Greased & PE Sheathed Strand Tendons Ungrouted Bar Tendons External Tendons (May be Grouted) Stress Increases are Distributed Along Tendon Length 3
- 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 4
- 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 5
- 6. Threadbar PT System Specifications 6
- 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 7
- 8. DYWIDAG MA Anchorage System 8
- 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 13
- 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 14
- 15. Typical PT Layout Details Typical Simple-Span Widening 15
- 16. Typical PT Layout Details Typical Simple-Span Widening 16
- 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 17
- 18. Common Design Issues Large Abutment Skew Angles Limited Abutment Diaphragm Thickness Large Blockout Depths Staggering of Blockouts at Sloped Exterior Girders 18
- 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. 19
- 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. 20
- 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. 21
- 22. Common Design Issues Hinges Adequate Stressing Clearance between Frames Vertical Clearance for Anchorages at Seat-end 22
- 23. Common Design Issues Horizontal Curvature Ducts Tied to Outside of Curve Duct Tie Reinforcement added for Horizontal Restraint 23
- 24. Problem Areas Anchor Zone Congestion Importance of Concrete Consolidation 24
- 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. 25
- 26. Problem Areas Where did my anchorages go? 26
- 27. Problem Areas They„re in here! 27
- 28. Thank You Contact us! - Preliminary Design Concerns - Unique Applications - Specification Development - Repair & Strengthening DSI is available to help. 28
- 29. Local Presence – Global Competence 29