Specifying Post-TensioningSpecifying Post Tensioning

Theodore L. Neff, P.E.Executive Director

Post-Tensioning Institute

Presentation Objectives

• Identify the most current & appropriate specs y pp p p

for different applications

• Highlight/ compare key provisions

• Discuss future issues & trends

Assuring Quality Post-Tensioning

PT Specifications

• Materials– Prestressing Steel– PT Coating

Sheathing– Sheathing– Anchorages & Couplers

• Fabrication• Fabrication– Shipping & Handling

• Construction• Construction– Installation– Stressingg– Finishing

Selecting the Right PT Specification

• Type of Application:– Bridges– Buildings/Parking Structures

Slab on Ground– Slab-on-Ground– Environmental Structures

• Exposure Conditions• Exposure Conditions– Aggressive– Non-aggressiveNon aggressive

• Special Site/ Project Requirements

PT SpecificationsScope – ACI 423.7

• ACI 423.7-07– Materials criteria & fabrication requirements for unbonded single-– Materials criteria & fabrication requirements for unbonded single-

strand tendons used in nonaggressive & aggressive environments.

– Not intended to apply to nonstructural elements and applications, pp y pp ,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 SpecificationsScope – PTI Unbonded Spec

• PTI M10.2-00 Specification for Unbonded Single Strand TendonsStrand 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 used only for control of crackingand post tensioning used only for control of cracking or deflection.

PT SpecificationsScope – 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 concreteconcrete

Selecting the Right PT SpecificationExposure Conditions-Buildings/Parking

• ACI 318-08:– 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:• ACI 423.7:– Aggressive environment—an environment in which structures

are exposed to direct or indirect applications of deicing h i l t b ki h t f thchemicals, 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 directlystructures where stressing pockets are wetted or are directly in contact with soils

Selecting the Right PT SpecificationExposure Conditions-SOG

• PTI Standard Requirements for Design of Shallow Post-Tensioned Concrete Foundations on Expansive Soils: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 fromthe 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.

6 2 2 2 U f l t d t d i f ith6.2.2.2 - Use of encapsulated tendons in conformance with ”Specifications for Single-Strand Unbonded Tendons”, Post-Tensioning Institute, May 2003, Section 2.2.6.

6 2 2 3 Other means of mitigating corrosion as appro ed b the6.2.2.3 – Other means of mitigating corrosion as approved by the Engineer.

PTI SOG Design StandardRecommended Minimum Concrete Cover

Standard Specifications for Unbonded TendonsMaterials

• ACI 423.7-07 Specification for Unbonded

Single-Strand Tendon Materials

• PTI M10 2-00 Specification for UnbondedPTI 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 SpecsPrestressing Steel

Photo Courtesy of G. Chacos

• ASTM A416/A416M Standard Specification for Steel Strand Uncoated Seven-Wire for Prestressed ConcreteStrand, Uncoated Seven-Wire for Prestressed Concrete

• A722/A722M Standard Specification for Uncoated High-p gStrength Steel Bar for Prestressing Concrete

A882/A882M St d d S ifi ti f Fill d E• A882/A882M Standard Specification for Filled Epoxy-Coated Seven-Wire Prestressing Steel Strand

• A475 Standard Specification for Zinc-Coated Steel Wire Strand

Unbonded Tendon Material SpecsAcceptance Criteria - Prestressing Steel

tabl

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tabl

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Acc

ept

Acc

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Unbonded Tendon Material SpecsPT Coating

• Type:– Moisture displacing– Corrosion inhibiting

• Application rate: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 SpecsSheathing

• Thickness :C– 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 SpecsAnchorages & Couplers

• Static test:

– Strength ≥ 95% of actual breaking strength*

– Elongation ≥ 2%Elongation ≥ 2%

F ti t t• Fatigue test:

– Test 1 – 500,000 cycles with

range of 60 to 65% MUTS

– Test 2 – 50 cycles withTest 2 50 cycles with

range of 40 to 80% MUTS

Unbonded Tendon Material SpecsEncapsulated Anchorages

Watertightness Test

• ACI 423/PTI:– 1 25 psi for 24 hours1.25 psi for 24 hours

• ACI 350:

– 10 psi for 24 hoursp

Post-Tensioning Systems & ApplicationsPresentation Outline

• Basic Conceptsp

• Post-Tensioning Systems– Unbonded

– Bonded

– External

Advantages/Disadvantages• Advantages/Disadvantages

• Applications

19

• Construction

Standard Specifications for Unbonded TendonsFabrication

• ACI 423.7-07 Specification for Unbonded Single-S d T d M i lStrand Tendon Materials

• PTI M10 2-00 Specification for Unbonded Single-PTI M10.2 00 Specification for Unbonded SingleStrand Tendons

• PTI Specification for Unbonded Single Strand Tendons for Slabs-on-Ground (Future-under d l t)development)

Standard Specifications for Unbonded TendonsFabrication - Certification

• ACI 423.7-07: shall be fabricated in a plant certified b ll di d liby an externally audited quality assurance program

• PTI M10 2-00: plants shall bePTI M10.2 00: plants shall be

1) Certified by PTI or,

2) Plant shall provide conclusive test data certified by an accredited laboratory that tendonsby an accredited laboratory that tendons meet requirements of spec

Standard Specifications for Unbonded TendonsFabrication – 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– 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 th d i ff t f di t li htthe damaging effects of direct sunlight

• ShippingN t lli ti d h ll b d– Nonmetallic tie-downs shall be used

– Protection shall be provided between trailer bed and bundles

Shipping of TendonsPhoto Courtesy of VSL

Standard Specifications for Unbonded TendonsConstruction

• 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 ApplicationsPrestressing Strand for Barrier Cable Applications

• PTI Specification for Unbonded Single Strand Tendons for Slabs-on-Ground (Future-under development)

Standard Specifications for Unbonded TendonsInstallation - Certification

• ACI 301-10: unless otherwise specified, l h ll b ifi d i d i h PTI‘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 TendonsInspection- Certification

• ACI 301-10: shall be performed by personnel ifi d i d i h h PTI’ L l 2 Pcertified in accordance with the PTI’s Level 2 Post-

Tensioning Inspector program or as otherwise specifiedspecified

• PTI M10.2-00: N/A

Standard Specifications for Unbonded TendonsInstallation- 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:Cover to tendon end:• ¾ in. for non-aggressive environments

• 1 in for aggressive environments1 in. for aggressive environments

Standard Specifications for Unbonded TendonsFixed-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

Pull Installation

Photos courtesy of G. Chacos

Push Installation

Field Installation

Standard Specifications for Unbonded TendonsSheathing 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

t t l d d l th i l th 2% f th t d l th• total damaged 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– 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 indamaged areas may be permitted without repair for tendons in a non-aggressive environment

Standard Specifications for Unbonded TendonsTendon 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;3/8 in. for member depth 8 in. and ≤ 2 ft; – 1/2 in. for member depth > 2 ft.

• Lateral deviationsLateral deviations– Radius of curvature ≥ 480 strand diameters– When radius of curvature < 480 strand diameters is

necessary provide additional hairpin reinforcement acceptednecessary, provide additional hairpin reinforcement accepted by Engineer

Standard Specifications for Unbonded TendonsStressing

ACI 301/PTI:• Jack calibration:

– Calibrated to known standards; – At interval ≤ 6 monthsAt interval ≤ 6 months

• Measured elongations– Within ± 7% of calculated elongation

– If > 7%, determine cause and correct discrepancy

Standard Specifications for Unbonded TendonsTendon Finishing

ACI 301/PTI:• Trimming Tendons:

– Strand length protruding beyond wedges shall be ≥ 0.5 in.– Maximum length shall comply with cover requirementsMaximum 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 pacceptance of measured elongation

– ACI 301/PTI – In aggressive environs,cut within 1 working daycut within 1 working day

Standard Specifications for Unbonded TendonsTendon Finishing

• Encapsulation caps:ACI 301– ACI 301 –

• Install within 8 hours• If capping is delayed, provide protection from moisture

PTI Commentary: install within 1 working day– PTI – Commentary: install within 1 working day

• Grouting of Stressing Pockets:g g– ACI 301 –

• Fill stressing pockets with non-metallic, non-shrink grout within one day after tendon cutting.g

• Grout shall not contain chlorides or other deleterious chemicals

• PTI - Fill stressing pockets with non-metallic, non-shrink grout within 10 days

after tendon cutting.

Standard Specifications for Unbonded TendonsConstruction – Special Applications

• PTI M10.4-07 Specification for Seven-Wire P i S d f B i C bl A li iPrestressing Strand for Barrier Cable Applications

• PTI Specification for Unbonded Single Strand p gTendons for Slabs-on-Ground (Future-under development)

• ACI 350 – xx Specification for Concrete Environmental Containment Structures (Future-Environmental Containment Structures (Futureunder development)

Post-Tensioning SpecificationsFuture Developments

• Specialty applicationsEnvironmental structures– Environmental structures

– Slab-on-ground– Other?

N f t• New formats– ASTM style (i.e. no commentary)– Master Spec– Construction-only

• Technical Issues– InspectionInspection– Grouting of pockets– Push-on wedge seating of fixed-end anchors

Sheathing materials– Sheathing materials– Anchorage testing– Strand testing

Questions!