Specifying Post-Tensioning Theodore L. Neff, P.E. Executive Director Post-Tensioning Institute
Presentation Objectives Identify the most current & appropriate p specs for different applications Highlight/ compare key provisions Discuss future issues & trends
Assuring Quality Post-Tensioning
PT Specifications Materials Prestressing Steel PT Coating Sheathing Anchorages & Couplers Fabrication Shipping & Handling Construction Installation Stressing Finishing
Selecting the Right PT Specification Type of Application: Bridges Buildings/Parking Structures Slab-on-Ground Environmental Structures Exposure Conditions Aggressive Non-aggressive Special Site/ Project Requirements
ACI 423.7-07 PT Specifications Scope ACI 423.7 Materials criteria & fabrication requirements for unbonded singlestrand tendons used in nonaggressive & aggressive environments. Not intended to apply to nonstructural elements and applications, which might include topping slabs, waterproofing slabs-on-fill, and post-tensioning used only for control of cracking or deflection. For nonflexural or membrane type structures primarily under tensile forces, the provisions apply where appropriate. Not intended for post-tensioned slabs-on-ground for light residential construction I d b f i ACI 318 d h Incorporated by reference in ACI 318 and hence indirectly in the International Building Code
PT Specifications Scope PTI Unbonded Spec PTI M10.2-00 Specification for Unbonded Single Strand Tendons Materials criteria, fabrication & installation requirements for unbonded single-strand tendons used in nonaggressive & aggressive environments. Intended for all common structural uses of unbonded PT tendons Includes post-tensioned slabs-on-ground for light residential construction Not intended to apply to nonstructural elements and applications, which might include topping slabs, waterproofing slabs-on-fill, and post-tensioning tensioning used only for control of cracking or deflection.
PT Specifications Scope ACI 301 ACI 301-10 Specifications for Structural Concrete Construction of cast-in-place and precast structural concrete and industrial floor slabs cast on ground. Section 9 covers requirements for post-tensioned, structural concrete
ACI 318-08: Selecting the Right PT Specification Exposure Conditions-Buildings/Parking 18.16.3 For applications in corrosive environments, the sheathing shall be connected to all stressing, intermediate and fixed anchorages in a watertight fashion. 18.16.4 Unbonded single-strand tendons shall be protected against corrosion in accordance with ACI 423.7. ACI 423.7: Aggressive environment an environment in which structures are exposed to direct or indirect applications of deicing chemicals, seawater, brackish water, or spray from these water sources; and salt-laden air as occurs in the vicinity of coastal ways. Aggressive environments also include structures where stressing pockets are wetted or are directly in contact with soils
Selecting the Right PT Specification Exposure Conditions-SOG PTI Standard Requirements for Design of Shallow Post- Tensioned Concrete Foundations on Expansive Soils: 6.2.2 - Soil Chlorides When concrete is in direct contact with soil containing concentrations of chloride ions in excess of 500 ppm, as determined by California DOT Test 4221 or other current test method recognized in the governing building code or commonly used in the geographic area of the project, the tendons and reinforcing steel shall be protected from corrosion by either 6.2.2.1, 6.2.2.2, or 6.2.2.3. 6.2.2.1 Use of minimum concrete cover in accordance with Table 1. 6222 6.2.2.2 - Use of encapsulated tendons in conformance with Specifications for Single-Strand Unbonded Tendons, Post- Tensioning Institute, May 2003, Section 2.2.6. 6223 Other means of mitigating corrosion as appro ed b the 6.2.2.3 Other means of mitigating corrosion as approved by the Engineer.
PTI SOG Design Standard Recommended Minimum Concrete Cover
Standard Specifications for Unbonded Tendons Materials ACI 423.7-07 Specification for Unbonded Single-Strand Tendon Materials PTI M10.2-00 Specification for Unbonded Single-Strand Tendons PTI M10.4-07 Specification for Seven-Wire Prestressing Strand for Barrier Cable Applications PTI Specification for Unbonded Single Strand Tendons for Slabs-on-Ground (Future-under ( development)
Unbonded Tendon Material Specs Prestressing Steel Photo Courtesy of G. Chacos ASTM A416/A416M Standard Specification for Steel Strand, Uncoated Seven-Wire for Prestressed Concrete A722/A722M Standard Specification for Uncoated High- Strength Steel Bar for Prestressing Concrete A882/A882M Standard d Specification for Filled Epoxy- Coated Seven-Wire Prestressing Steel Strand A475 Standard Specification for Zinc-Coated Steel Wire Strand
Unbonded Tendon Material Specs Acceptance Criteria - Prestressing Steel Accept table Accept table
Unbonded Tendon Material Specs PT Coating Type: Moisture displacing Corrosion inhibiting Application rate: 2.5 lbs. per 100 ft (0.5 in. diameter strand) 3.0 lbs. per 100 ft (0.6 in. diameter strand) Performance Criteria: Dropping point & Oil separation Flash point Soak test Corrosion test Sheathing compatibility
Unbonded Tendon Material Specs Sheathing Thickness : ACI 423.7 Minimum: 50 mils SOG: N/A PTI Minimum: 50 mils SOG: 40 mils Diameter: 0.030 in. > maximum strand diameter (ACI/PTI) Material: Polypropylene or polyethylene (ACI/PTI)
Unbonded Tendon Material Specs Anchorages & Couplers Static test: Strength 95% of actual breaking strength* Elongation 2% Fatigue test: t Test 1 500,000 cycles with range of 60 to 65% MUTS Test 2 50 cycles with range of 40 to 80% MUTS
Watertightness Test ACI 423/PTI: 1.25 psi for 24 hours Unbonded Tendon Material Specs Encapsulated Anchorages ACI 350: 10 psi for 24 hours
Post-Tensioning Systems & Applications Presentation Outline Basic Concepts Post-Tensioning Systems Unbonded Bonded External Advantages/Disadvantages Applications Construction 19
Standard Specifications for Unbonded Tendons Fabrication ACI 423.7-07 Specification for Unbonded Single- Strand Tendon Materials PTI M10.2-00 Specification for Unbonded Single- Strand Tendons PTI Specification for Unbonded Single Strand Tendons for Slabs-on-Ground (Future-under development)
Standard Specifications for Unbonded Tendons Fabrication - Certification ACI 423.7-07: shall be fabricated in a plant certified by an externally audited d quality assurance program PTI M10.2-00: plants shall be 1) Certified by PTI or, 2) Plant shall provide conclusive test data certified by an accredited laboratory that tendons by an accredited laboratory that tendons meet requirements of spec
Standard Specifications for Unbonded Tendons Fabrication Handling & Storage Handling Shall not be damaged during handling, loading, or moving at supplier s facility Metal chokers or chains shall not be used to lift tendons or tendon bundles Storage Shall be protected from exposure to rain, snow, deicing salts, and other corrosive elements Tendons stored for 1 month or longer shall be protected from the damaging effects of direct sunlight Shipping Nonmetallic tie-downs shall be used Protection shall be provided between trailer bed and bundles
Shipping of Tendons Photo Courtesy of VSL
Standard Specifications for Unbonded Tendons Construction ACI 301-10 Specifications for Structural Concrete PTI M10.2-00 Specification for Unbonded Single- Strand Tendons PTI M10.4-07 Specification for Seven-Wire Prestressing Strand for Barrier Cable Applications PTI Specification for Unbonded Single Strand Tendons for Slabs-on-Ground (Future-under development)
Standard Specifications for Unbonded Tendons Installation - Certification ACI 301-10: unless otherwise specified, personnel shall be certified in accordance with PTI s Level 1 Unbonded PT- Field Installation program PTI M10.2-00: unless otherwise specified, performed by PTI Certified Installer
Standard Specifications for Unbonded Tendons Inspection- Certification ACI 301-10: shall be performed by personnel certified in accordance with the PTI s Level 2 Post- Tensioning Inspector program or as otherwise specified PTI M10.2-00: N/A
Standard Specifications for Unbonded Tendons Installation- Anchorages ACI 301/PTI: Concrete cover to wedge cavity: 1-1/2 in. for non-aggressive environments 2 in. for aggressive environments Cover to tendon end: ¾ in. for non-aggressive environments 1 in. for aggressive environments
Standard Specifications for Unbonded Tendons Fixed-End Anchorages Wedge-type anchorages ACI 301: When using the pull-on method, seat fixed-end wedges with a force between 80 and 85% of MUTS. When permitted, other methods shall be substantiated by testing acceptable to Architect/Engineer. PTI: Shall be seated with a load of 80 to 85% MUTS
Fixed-End Anchor Photos courtesy of G. Chacos Pull Installation Push Installation Field Installation
Standard Specifications for Unbonded Tendons Sheathing Repair ACI 301: Non-aggressive environments -- small tears up to 3 in. long shall be allowed without repair if: damage is spaced a minimum of 8 ft apart and total t damaged d length is less than 2% of the tendon length. Sheathing damage in excess of the above shall be repaired Repair a breach or circumferential split in sheathing Aggressive environments -- repair all damage to sheathing PTI: Damaged areas shall be repaired by restoring the P-T coating in the damaged area and repairing the sheathing Commentary: with the Engineer s acceptance small damaged areas may be permitted without repair for tendons in a non-aggressive environment
Standard Specifications for Unbonded Tendons Tendon Tolerances ACI 301/PTI: Profile deviations shall not exceed: 1/4 in. for member depth 8 in.; 3/8 in. for member depth > 8 in. and 2 ft; 1/2 in. for member depth > 2 ft. Lateral deviations Radius of curvature 480 strand diameters When radius of curvature < 480 strand diameters is necessary, provide additional hairpin reinforcement accepted by Engineer
Standard Specifications for Unbonded Tendons Stressing ACI 301/PTI: Jack calibration: Calibrated to known standards; At interval 6 months Measured elongations Within ± 7% of calculated elongation If > 7%, determine cause and correct discrepancy
Standard Specifications for Unbonded Tendons Tendon Finishing ACI 301/PTI: Trimming Tendons: Strand length protruding beyond wedges shall be 0.5 in. Maximum length shall comply with cover requirements Timing: ACI 301 - Provide protection to prevent moisture from reaching the anchorages if cutting is delayed more than 10 days after stressing PTI - Cut as soon as possible after acceptance of measured elongation ACI 301/PTI In aggressive environs, cut within 1 working day
Standard Specifications for Unbonded Tendons Tendon Finishing Encapsulation caps: ACI 301 Install within 8 hours If capping is delayed, provide protection from moisture PTI Commentary: install within 1 working day Grouting of Stressing Pockets: ACI 301 Fill stressing pockets with non-metallic, non-shrink grout within one day after tendon cutting. Grout shall not contain chlorides or other deleterious chemicals PTI - Fill stressing pockets with nonmetallic, non-shrink grout within 10 days after tendon cutting.
Standard Specifications for Unbonded Tendons Construction Special Applications PTI M10.4-07 Specification for Seven-Wire Prestressing Strand for Barrier Cable Applications i PTI Specification for Unbonded Single Strand Tendons for Slabs-on-Ground (Future-under development) ACI 350 xx Specification for Concrete Environmental Containment Structures (Future- Environmental Containment Structures (Future under development)
Post-Tensioning Specifications Future Developments Specialty applications Environmental structures Slab-on-ground Other? New formats ASTM style (i.e. no commentary) Master Spec Construction-only Technical Issues Inspection Grouting of pockets Push-on wedge seating of fixed-end anchors Sheathing materials Anchorage testing Strand testing
Questions!