post tensioning

IES Post-Tensioning Evening Talk Quality Control & Measures for Prestressing Works, Tommy Lee 1

Quality control & Measures for Quality control & Measures for PrestressingPrestressing worksworks

Tommy Lee, VSL SingaporeTommy Lee, VSL Singapore


ContentsContents1.1. Introduction Introduction 2.2. Workmanship ControlWorkmanship Control3.3. PT System Testing PT System Testing 4.4. PT Components Production ControlPT Components Production Control5.5. Good Practice on Site for Slab PT workmanshipGood Practice on Site for Slab PT workmanship

a.a. 1 case of accident (at time of stressing) 1 case of accident (at time of stressing) 6.6. ConclusionConclusion7.7. Q & AQ & A


IntroductionThis presentation emphasizes the need for Quality control in PT and the importance in systematic approach in achieving quality assured PT systems and operations.


- stressed by un-qualified contractor & personnel, - using rented equipment and working to local specifications

Workmanship


Workmanship

Post-Tensioning ducts & strands installed and stressed by un-qualified contractor in Russia.


Workmanship


Workmanship

Post-Tensioning tendon grouted by un-qualified contractor in United Kingdom using simple cement slurry: Picture show situation after 7 years


What can be done to stop such poor workmanship?


Execution of the works and the qualification of installers is an area regulated by the national provisions of the EU Member States Interest of some EU Member States to have European Standard on installation and qualification of personnel and PT companies First step was to create a voluntary document : CEN (European Committee for Standardization) Workshop Agreement, CWA 14646 (no official standard) CWA 14646 may be transformed into prENV etc and thus become European Standard in future

Installation and qualification of personnel and PT companies


PT Specialist Contractor :

Contractor or construction enterprise which carries out installation, stressing, and filling of duct of the PT system Having qualified, well trained, and experienced personnel thoroughly familiar with the PT system Trains and qualifies skilled specialists Any work on site executed only under supervision of qualified and experienced PT supervisor or PT site manager (certified personnel)




PT Specialist company

Quality Assurance

Logistics Site OperationTechnical


PT System Testing


PT System Failure


How can we ensure the safety of the workers when using PT Systems? Safety cannot be

compromise.


CPD = Construction Products Directive :Bring to single European market construction products

which are fit for use i.e. when installed in the construction works. They

satisfy the 6ERs (Essential Requirements)

Such products obtain CE marking for identification

CPD = Construction Products Directive :Bring to single European market construction products

which are fit for use i.e. when installed in the construction works. They

satisfy the 6ERs (Essential Requirements)

Such products obtain CE marking for identification

Works

Introduction and legal background of ETAs


EUs regulationsConstruction Products Directive 89/106/EEC

European Organization for Technical Approval (EOTA)

European Committee for Standardization (CEN)

European Tech. Approval Guidelines (ETAG)

(i.e. ETAG013- for PT Interpretative Document)

European Standards


Construction Products Directive

ETAG013 covers all relevant essential requirements of CPD for Post-tensioning kits


ETAG 013


Use categories are :

Internal bonded tendons (concrete and composite structures)

Internal unbonded tendons (concrete and composite structures)

External tendons (concrete and composite structures)

Scope and content of ETAG013


Scope and content of ETAG013Optional use categories are :

(a) Restressable tendon (internal and external)(b) Exchangeable tendon (internal and external)(c) Tendon for cryogenic applications(d) Internal bonded tendon with plastic duct(e) Encapsulated tendon(f) Electrically isolated tendon(g) Tendon for use in structural steel and composite

construction as external tendon(h) Tendon for use in structural masonry construction as

internal and/or external tendon(i) Tendon for use in structural timber construction as

internal and/or external tendon


Post-Tensioning Kits comprise: Tensile elements (strand, wire, bar) made of prestressing

steel, monostrands Anchorages (stressing and fixed) Couplings (movable and fixed) Ducts made of steel strip Steel pipe Plastic pipe Corrugated plastic ducts Special Filling materials Bursting reinforcement Special accessories (vents, supports, caps,...)



ETA can be obtained for :

Kit containing tensile elements, anchorages, couplings, ducts, filling material, deviators, bursting steel, and special accessoriesSpecial filling materials as specified in (Grease, wax, special grout)

N.B.: PT kits can be used for any type of structure. However, ground anchors and stay cables are not covered



Requirements, assessment, acceptance criteria


Required tests :

Resistance to Static load Resistance to Fatigue Load transfer to the structureFriction coefficient along tendon path and in anchoragesDeviation/ deflection limitsPracticability/ reliability of installationOther Optional tests are also listed for considerations



Requirements, assessment, acceptance criteriaResistance to static load :



Resistance to static load - Acceptance criteria :

Maximum load 95% of actual tensile strength of

prestressing steel

Total elongation of prestressing steel 2%

Failure by fracture of prestressing steel

Acceptable residual deformations of anchorage components after testing

Deformations in anchorage components shall stabilise at load held at 80% GUTS


Requirements, assessment, acceptance criteriaResistance to fatigue :


Requirements, assessment, acceptance criteriaRequirements, assessment, acceptance criteriaResistance to fatigue - Acceptance criteria :

No fatigue failure in anchorage components

No more than 5% of tensile element cross section lost during fatigue test at 2x106 cycles with 80 MPa stress range at maximum load of 65% characteristic strength of prestressing steel


Requirements, assessment, acceptance criteriaRequirements, assessment, acceptance criteriaLoad transfer to structure :Load transfer to structure :

Test to be performed at minimum concrete strength specified for transfer of prestressing


Load transfer to the structure (mechanical and Load transfer to the structure (mechanical and bond anchorages)bond anchorages)

Load transfer to structure - Acceptance criteria :

Crack width at 1st time to 80% GUTS 0.15mm

Crack width at 10th time to 12% GUTS 0.15mm

Crack width at 10th time to 80% GUTS 0.25mm

Strain and crack readings shall stabilise Ultimate force in test Fu

1.1 Fpk (f cm,e / f cm,0)

Slip of bond anchorages shall stabilise

Requirements, assessment, acceptance criteriaRequirements, assessment, acceptance criteria


Actual material characteristics of components used for testing shall be determined and documented

Test results shall be submitted for compulsory requirements (static load, fatigue, load transfer)

Analysis and comparison with experience is acceptable for other requirements and optional use categories

Acceptance of test data in accordance with `The provision of data for assessments leading to ETA

List of requirements applies for initial request for ETA. Renewal of ETA requires no testing but submittal of past experience. Extension of ETA may require testing for modifications

ETA Submission summary


PT Components Production Control (under ETAG013)


Approval and certification procedures

Attestation and evaluation of conformity Tasks of kit manufacturer :

Keep updated list of all component manufacturers (copy to CB) Audit of each component manufacturer each year (copy of audit report to CB) Take specimens each year from at least one job site and perform a series of single strand tensile element tests as per Annex E.3 (copy of report to CB) Keep all results available for at least 10 years Factory production control (may comply with ISO 9001)


Factory production control (may comply with ISO 9001), including :

- Incoming materials- Inspection and testing during production- Control of non-conforming products- Complaints




-Incoming, Inspection and testing plan


Attestation and evaluation of conformity - Tasks of kit manufacturer : Inspection and testing plan


Approval and certification proceduresAttestation and evaluation of conformity Tasks for the Cerfication body- : Continuous surveillance


ETAG 013


Approval and certification procedures

ETA Content :

ETA text (general document for external use) Additional information (held available for distribution to users unless it is confidential) Confidential information (manufacturing drawings, material specifications) needs to be deposited with AB and CB. These are confidential and proprietary and shall not be given to other parties


Attestation and evaluation of conformity CE Marking

Name of kit manufacturer Year when marking was affixed Number of Certificate of Conformity ETA-number The use category(ies) The number of the CB


Good Practice for Slab Post- Tensioning -Workmanship


Workmanship


Standards for Post- tensioning kits

ElementsElements StandardsStandardsHigh tensile steel and strand for High tensile steel and strand for prestressingprestressing of of concreteconcrete

BS 5896BS 5896--1980, pr EN 10138, ASTM A416, 1980, pr EN 10138, ASTM A416, JISG3536, ISO 156303JISG3536, ISO 156303

PrestressingPrestressing steel, including individually steel, including individually greased and sheathed greased and sheathed monostrandsmonostrands (excl. filling (excl. filling material)material)

prENprEN 10138 part 110138 part 1--4 (part 3 covering strands)4 (part 3 covering strands)

Post tensioning systemsPost tensioning systems EN 13391EN 13391--2004 (replace BS 4447)2004 (replace BS 4447)

Steel ducts (steel strip sheaths)Steel ducts (steel strip sheaths) EN 523EN 523--20032003

Steel pipeSteel pipe prENprEN 1025510255

Corrugated Plastic ducts (for internal tendons)Corrugated Plastic ducts (for internal tendons) Fib technical report, bulletin 7 (some parts do Fib technical report, bulletin 7 (some parts do not apply to ETAG 013)not apply to ETAG 013)

Smooth Plastic ducts (for external tendons)Smooth Plastic ducts (for external tendons) prENprEN 12201 part 1 and part 212201 part 1 and part 2

Bursting reinforcementBursting reinforcement prENprEN 10080, EN 1002510080, EN 10025

Grout for Grout for prestressingprestressing tendonstendons EN 445EN 445--2007, EN 4462007, EN 446--2007, EN 4472007, EN 447-- 2007(replace 1996 versions)2007(replace 1996 versions)


Strand- Quality ControlStrand Compliance to StandardASTM A416 / ISO 156303 / BS 5896/PrEN10138/JISG3536- Quality Check Test Certificates ( Tensile strength, Yield

strength, Relaxation test ( max 2.5% after 1000h at 70%UTS)- Visual Check Mechanical Damage- Tolerance on Strand diameter- Corrosion protection ( water soluble oil) at supply stage or

Installed cable with VpCl powder if the tendons are grouted after 2 -6 weeks.

- Storage of Strands


ContentContent

1.01.0 -- Before ConcretingBefore Concreting

2.0 2.0 After ConcretingAfter Concreting

3.0 3.0 Before StressingBefore Stressing

4.0 4.0 Jack InstallationJack Installation

5.0 5.0 After StressingAfter Stressing

6.0 6.0 After Stressing 1 hourAfter Stressing 1 hour


1.0 - Before ConcretingLeading hand & worker should check no damages in tendon ducting.

Correct tendon profile? Duct Secured? Any damage? Any Kink? Continuity of duct?


1.0 - Before ConcretingEngineer should check the installation of anti-bursting reinforcement.

Correct Spacing? Bar Type? Spiral or Stirrup? Steel Grade?

Number of links?


2.0 After ConcretingWorker should check the anchorage component condition during installation

Any concrete slurry on surface? (If need clean off, dont hammer casting violently )

If any major cracks / voids noted inform supervisor


3.0 Before Stressing

- Foreman should explain the stressing sequence to workers

- Foreman should ensure all persons aware of planned stressing sequences and possible interfaces between teams etc. and confirm communication systems.

- Necessary Signage shall be clearly displayed.

Understand?

How to communicate?


3.0 Before StressingEngineer and foreman should check stressing sequence

(e.g. To ensure no persons Avoid standing behind the stressed strand within the specified of times)


3.0 3.0 Before stressingBefore stressing

Stressing worker should carry out preStressing worker should carry out pre--work visual inspection of work visual inspection of equipment and a trial run of jack without loading are carried ouequipment and a trial run of jack without loading are carried out to t to check the condition of the cable, jack, pump, hose and gauge.check the condition of the cable, jack, pump, hose and gauge.



Foreman and leading hand should checkForeman and leading hand should check

Engineer and Foreman should check strength of concrete and gain Engineer and Foreman should check strength of concrete and gain approval from main contractor / consultantapproval from main contractor / consultant

Any honeycomb, crack, void ?Any honeycomb, crack, void ?



Foreman & Leading Hand should check correct warning sign.Foreman & Leading Hand should check correct warning sign.

Correct Sign? Enough Sign? Placed in a correct position?Correct Sign? Enough Sign? Placed in a correct position?


4.0 4.0 Jack InstallationJack Installation

Before jack installation, stressing worker should reBefore jack installation, stressing worker should re--check check installed wedges in anchorage.installed wedges in anchorage.

Wedge in pair? Wedge inside anchor block & even? Wedge in pair? Wedge inside anchor block & even? Cavity is clean? Correct wedge type?Cavity is clean? Correct wedge type?


4.0 Jack Installation

Worker must stand on the two sides, in other words clear of the jack. (i.e.. not hit by falling jack)

Pump operator and jack operator shall establish good communication link


4.0 During Stressing

No holding of jacks allowed during stressing

Workers by the side of jack, never walk pass the tendon


4.0 During StressingLook out man required for two end stressing anchorage

Inform supervisor if there are circumstances which may lead to

slippage or

failure of the stressed tendon


4.0 During Stressing

Stressing of two adjacent tendons by two stressing teams not allowed


4.0 During StressingFollow the stressing sequence and report the stressing status at the required times to the in charge.


5.0 After Stressing

- Stressed tendon not accessible after 1 hour

- Protective barriers shall be placed at end of tendon used with stressing anchorage


6.0 6.0 After Stressing 1 hourAfter Stressing 1 hourForeman / leading hand should checkForeman / leading hand should check

concrete surface near anchorage zone (any crack?) concrete surface near anchorage zone (any crack?)

check the condition of anchorage and stressed tendoncheck the condition of anchorage and stressed tendon

Only perform checks from the side of stressed tendonOnly perform checks from the side of stressed tendon


6.0 After Stressing 1 hour

- Re-check the time record of tendon.

If all OK, remove protective barriers and resume operations.

- If not, protective barriers remain and other operations cannot proceed


What could go Wrong?

Tendon 32

Tendon 31


What Could go Wrong?

Tendon 31.Tendon 31.

Tendon 32Tendon 32


What could go wrong?


Conclusion Practicing good Quality Control in PT enhances

safety It is a complex but manageable task Poorly installed PT systems/ components will

compromise safety of human lives Quality control requirements shall be measurable

and verifiable. BCA is moving towards adopting Eurocodes for

Design and the study of similar nature to ETA for PT system


Q & A

Quality control & Measures for Prestressing worksTommy Lee, VSL SingaporeContentsIntroductionSlide Number 4Slide Number 5Slide Number 6Slide Number 7Slide Number 8Installation and qualification of personnel and PT companiesSlide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14PT System FailurePT System FailurePT System FailureSlide Number 18Slide Number 19EUs regulationsConstruction Products DirectiveETAG 013Scope and content of ETAG013Scope and content of ETAG013Scope and content of ETAG013Scope and content of ETAG013Requirements, assessment, acceptance criteriaSlide Number 28Requirements, assessment, acceptance criteriaRequirements, assessment, acceptance criteriaRequirements, assessment, acceptance criteriaRequirements, assessment, acceptance criteriaSlide Number 33Slide Number 34Slide Number 35Slide Number 36Slide Number 37Slide Number 38Slide Number 39Attestation and evaluation of conformity - Tasks of kit manufacturer : Inspection and testing planSlide Number 41ETAG 013Slide Number 43Approval and certification proceduresSlide Number 45Slide Number 46Slide Number 47 Standards for Post- tensioning kitsStrand- Quality ControlContent 1.0 - Before Concreting1.0 - Before Concreting2.0 After Concreting3.0 Before Stressing3.0 Before Stressing3.0 Before stressing3.0 Before Stressing3.0 Before Stressing4.0 Jack Installation4.0 Jack Installation4.0 During Stressing4.0 During Stressing4.0 During Stressing4.0 During Stressing5.0 After Stressing6.0 After Stressing 1 hour 6.0 After Stressing 1 hour What could go Wrong? What Could go Wrong?What could go wrong?ConclusionSlide Number 72

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