P B TENS-PRA 001-Cefreyssinet.honlap.hu/pages/freyssinet/contents/static/15/doc/lapos... · ENV 13670-1 – Execution of concrete structures. 3 RESSOURCES – EQUIPMENT - All jacks

FREYSSINET INTERNATIONAL & Cie – TECHNICAL DEPARTMENT 1 bis rue du Petit Clamart – B.P. 135 78148 VELIZY-VILLACOUBLAY Tel. : 33 1 46 01 85 10 – Fax : 33 1 46 01 86 52

PROJET, LOT, TITRE, TYPE DE DOC. / PROJECT, SCOPE, TITLE, DOC. TYPE__

WORK PROCEDURE

B RANGE ANCHORAGES

Tensioning Operations

PAYS / COUNTRY MOA / CLIENT MOE / CONTRACTOR

-

- -

FREYSSINET INTERNAL REVISION STATUS_ E

D

C 29/08/11 NDY PSN IZC §3 / §4 / §5 / Appendix 2

B 26/11/10 NDY PSN IZC §6 figure / §7 injection

A 18/11/10 NDY PSN IZC FIRST ISSUE

REV. DATE RÉDIGÉ PAR

/ WRITTEN BY

VÉRIFIÉ PAR

/ CHECKED BY

APPROUVÉ PAR

/ APPROVED BY MODIFICATION

FREYSSINET DOCUMENT N° REVISION

P B TENS-PRA 001 C

Quality Management System certified by BUREAU VERITAS Certification PAGE / SHEET

1 / 15

This document is the exclusive property of FREYSSINET. It is confidential and may not be used, reproduced or communicated either in whole or in part, in any form or manner without the prior written agreement of FREYSSINET. This document shall not be distributed to third parties except under the terms of the contract.

WORK PROCEDURE – B RANGE ANCHORAGES

Tensioning Operations –

P B TENS-PRA 001 – Rev. C Quality Management System certified by BUREAU VERITAS Certification Page 2/15


REV.

CONTENTS

1 PURPOSE........................................................................................................3

2 REFERENCES .................................................................................................3

3 RESSOURCES – EQUIPMENT .......................................................................3

4 TENSIONING OPERATIONS PREPARATION................................................4

4.1 Anchorage parts storage...........................................................................4

4.2 Tensioning operations start.......................................................................4

4.3 Preliminary checks....................................................................................4

5 TENSIONING OPERATIONS...........................................................................5

5.1 Checking before stressing ........................................................................6

5.2 First stage stressing..................................................................................6

5.3 Final tension .............................................................................................7

5.4 Strands overlength cut-off.........................................................................8

6 GROUTING ......................................................................................................8

7 UNBONDED STRANDS...................................................................................8

APPENDIX 1: CALCULATION OF TENSIONING PARAMETERS......................10

APPENDIX 2: TENSIONING RECORD SHEET...................................................12

APPENDIX 3: STRAND TENSIONING EQUIPMENT ..........................................14





REV.

1 PURPOSE The purpose of this procedure is to give instructions for the tensioning of internal

prestressing tendons composed of B13 or B15 anchorages and T13 or T15 strands. Strands

may be bare strands or monostrands (individually polyethylene sheathed and greased

strand called also unbonded strands) depending on the application.

The tendon tensioning operations must be carried out under the responsibility of a qualified

personnel, known as the PT supervisor (CMP).

2 REFERENCES Note : Documents mentioned within this procedure are cited without revision references or

with the revision current when going to press. Users of this work procedure should ensure

that the latest revision of any relevant document is used.

The reference documents are the following :

� CWA 14646 – Requirements for the installation of post-tensioning kits for

prestressing of structures and qualification of the specialist company and its

personnel,

� ENV 13670-1 – Execution of concrete structures.

3 RESSOURCES – EQUIPMENT

- All jacks used during the tensioning operations shall be monostrand stressing jacks

equipped with adapted nose for B range anchorages. Stressing jacks shall be

equipped with either mechanical wedge blocking system (spring) or hydraulic

wedge blocking system.

- All equipment used must be accompanied by their current certificate of

calibration. According to the regulations, jacks must be calibrated every 6 months

or 100 tensioning operations. It may be necessary to recalibrate the jacks on site. In

this case, calibration must be carried out in accordance with the instructions in

procedure P C ETVE PRA 501 – Opposition method jack calibration.

The calibration certificate for the tensioning pressure gauges must be less than 6

months old or must be checked every 100 tensioning operations. It can be checked

on site using a calibration pressure gauge, as specified in procedure P C ETMA

PRA 502 - Calibration of pressure gauges.

The calibration pressure gauge itself must be calibrated every year in a laboratory.

- All equipment must be used regularly.

C





REV.

4 TENSIONING OPERATIONS PREPARATION

4.1 Anchorage parts storage Following recommendations apply during the storage period.

- Light surface oxidation on anchorage blocks is allowed provided it can be removed

at the time of installation by means of a cleaning rag.

- Light oxidation on wedges is allowed provided it can be removed using an oil cloth

at the time of installation.

- Surface oxidation on trumplate is tolerated, except scaly rust.

4.2 Tensioning operations start - The team in charge of the operation must be or have been trained for tensioning

operations, and associated safety precautions.

- The tensioning order, method, force and theoretical elongation must be available

and known.

Tensioning parameters (final pressure, theoretical elongation to observe...) based on

project designer’s data are to be followed and reported in the tensioning record

sheet are given in appendix 1,

- The tensioning record sheet must be correctly prepared as described in appendix 2.

- It is always preferable to test the equipment before performing the first operation,

in order to check that it is operating satisfactorily and that all the parts are available

on site.

- Authorisation to start tensioning operations shall be given after checking of

concrete compressive strength and all project requirements.

4.3 Preliminary checks The following checks shall be done before to start the tensioning operations.

Tensioning operation is a highly sensitive operation. It is important for safety of personal

as well as for safety of the structure to perform all following checks before to proceed:

- The safety precautions must be known and followed by all personnel,

- The tensioning record sheet must be correctly prepared and given to the PT

supervisor,

- The jack hydraulic hoses and fittings are checked,

- The stressing jack, its handling and suspension equipment as well as the power

supply must have been checked, and work properly,

- The strands installed in the anchorage must be in compliance with the project

specification as steel grade, diameter, strands number, surface state, etc.

- The anchorage components must be in compliance with the project specification

drawing as type, unit, number and distribution, and be correctly positioned in the

structure,

- The equipment must be appropriate to the anchorage type (jack adaptations for B13

or B15 anchorages), and in sufficient quantity regarding with the tensioning method

and schedule,

C





REV. - Strand overlength shall be adapted to stressing jack used (see appendix 3),

- Equipment must be accompanied by the necessary current calibration certificates

(jacks and pressure gauges). See §3 for details about calibration of the equipment,

- Any external constraints such as, for example, form stripping, decentring, periods

between phases, etc., must have been taken into account,

- The temperature conditions must be acceptable, tensioning must not be carried out

below minus 10°C (-10°C).

5 TENSIONING OPERATIONS Three different cable anchoring configurations can be encountered.

- The general case is one end stressing of the tendon, with dead end onion anchorage

as shown hereafter: F

The two others configurations are with B range anchorages at both ends of the tendon.

- One end stressing with passive B anchorage : F

- Both ends stressing: F F

The tensioning operation is generally carried out in two stages.

- At the first stage stressing, all strands are tensioned up to 25% of the prestressing

final force.

First stage stressing can be done as soon as the concrete compressive strength is

attained, according to tensioning schedule. The minimum concrete compressive

strength at the time of first stage stressing shall be equal to 47% of the minimum

compressive strength required for final stressing (see table hereafter).

- Final stressing is done when concrete has reached its design compressive strength

or the minimum compressive strength as given in the table hereafter, according to

design requirements. Strands are then tensioned up to final load (force), as specified

at the design stage.

During the final stressing operation, elongation of the strands is controlled by

means of a paint mark made on the strand, as described in the paragraphs below.

C





REV. In addition, each strand mark will allow to check that all strands of the tendon have

been stressed.

Strand T13/T13S T15 T15S

Concrete compressive strength (cylinder) 20MPa 22MPa 23.5MPa

Concrete compressive strength (cube) 25MPa 27.5MPa 29MPa

5.1 Checking before stressing In any cases, it must be checked right before the tensioning operations that anchorage

block holes and wedges are exempt of corrosion, and that anchorage block holes and

wedges have not been greased. Wedges shall be used as oiled from the bucket. If those

conditions are not fulfilled, tensioning operations shall not be performed before adapted

corrective actions have been applied.

For tendons, with B anchorages at both ends, the wedges at passive end are hammered

before stressing operations and at 50 bar pressure in monostrand jack.

5.2 First stage stressing A first stage stressing up to 25% of the final load is performed providing that concrete has

reached the minimum compressive strength.

First stage stressing is done following the sequence here below:

- Checking of the good positioning of the anchorage block on the guide (trumplate)

sitting recess in horizontal and vertical directions (see important note),

- Stressing each strand up to 25% of the prestressing final force, respecting the

sequence given hereafter,

- Mechanical (with spring) or hydraulic locking-off of the wedge. Self wedge

anchoring and hammering are not allowed at active stressing anchorage.

Important notes:

The anchorage block well positioning needs to be checked before, during and after

tensioning operations of each strand. Operators must ensure that the anchorage block is

well centred: horizontally and vertically onto the guide bearing surface (recess) for

anchorage block. This shall be notified in the tensioning record sheet.





REV. During the stressing operation, the jack shall never reach the end of its stroke. A sudden

pressure increase in the jack without the piston moving would happen, that may lead to the

jack damage.

During the tensioning operations, standing behind the jacks is absolutely prohibited.

The operator must not have any part of his body behind or above the previously stressed

strands in the tendon.

No individual not required for the work operation must be anywhere near the area adjacent

to the tendon being stressed.

5.3 Final tension Tensioning operation is done following the sequence here below:

- Measure the initial overlength of the strands between the paint marks and the

bearing face of the anchorage (Dinitial), report them on the tensioning sheet,

- Strands tension up to final stressing force (i.e. final pressure P0) following the

sequence given in §5.2,

- Mechanical or hydraulic locking-off of the wedges according to the jack used,

- Release the pressure in the tensioning chamber to 50 bar and measure gross

pull-in. This value with the correction term indicated in appendix 1 gives the

net pull-in. Control that the net pull-in is within the range indicated in the table

below.

If net pull-in is not correct, tension again the strand up to P0, then reblock the

jaws if possible with the jack used, and control the pull-in again,

With hydraulic

locking-off

Without hydraulic

locking-off

Strand diameter T13 T15 T13 T15

min 4 mm 4 mm 6 mm 6 mm

mean 5 mm 6 mm 7 mm 8 mm

Pull-in at

stressing

anchorage

(mm) max 6 mm 8 mm 8 mm 9 mm

- Remove the jack,

Measure the final length (Dfinal) between the paint marks and the bearing face of

the anchorage.

- Write down the value (Dfinal – Dinitial) on the tensioning record sheet. This

elongation must be comprised between 0,95 ∆0 and 1,10 ∆0, with ∆0 as

calculated in appendix 1.

Important: During the stressing operation, the jack shall never reach the will happen, that

may lead to the jack damage.

During the tensioning operation, standing behind the jacks and anywhere around in the

structure in the area adjacent to the tendon is absolutely prohibited.





REV.

5.4 Strands overlength cut-off After checking of the tendon elongation compliance, strands overlength are cut-off with a

disk cutter.

Strands are cut-off to a distance of approximately 30mm behind the jaws.

Note 1: The strand overlengths of a non-compliant tendon must not under any

circumstances be cut off without the written agreement of the project manager.

Note 2: The strand overlengths must be cut off using an electric cutting disc, and

never with a blowtorch.

6 GROUTING Grouting operation is carried out using the vents / injection points located on the guides

(see figure below), with a cement grout complying with the project specifications and

standard.

Grout vent at the top of the guide shall be tightly protected in order to avoid concrete

introduction in the anchorage area, as represented in the figure below.

7 UNBONDED STRANDS Unbonded strands (monostrands) can be used for prestressing tendons with B anchorages.

Monostrands can be:

- contained in a general duct and cement grouted (as for tendons composed of

bare strands),

- directly casted in the concrete of the structure without using general duct.

In both cases, the tensioning operation is performed as described in §4 and §5.

After the completion of the tensioning operation and its validation then cut-off of the

strands overlengths is carried out, anchorage area shall be injected with cement grout.

Note concerning the use of unbonded strands without duct:

Injection tube

connected to the vent

of the guide Tight protection





REV. In the case of use of unbonded strands without duct, back side of the guide shall be tightly

obstructed in order to avoid concrete introduction in the anchorage area, as represented in

the figure below.





REV.

Appendix 1: CALCULATION OF TENSIONING PARAMETERS

FRICTION LOSSES Three types of friction losses are distinguished :

K1 : Friction in the guide,

K2 : Friction between the strands and the anchorage,

K3 : Internal friction of the tensioning jack.

The values of K1 and K2 vary with the surface condition of the parts in contact. The

minimum friction values correspond to the surface condition of a non deteriorate

anchorage and maximum values correspond to anchorage with acceptable deterioration of

the surface condition. The values of the three coefficients are given below.

- In the anchorage area

Depending on the case, mechanical friction (K1+K2) is as follows :

Bare strands Monostrands UNIT

Min Max Min Max

B range (T13/T15) 2% 3% 1% 2%

- In the tensioning jack

The internal friction K3 is measured in the laboratory at the jack calibration stage. The

value of this coefficient is delivered with each jack.

If the jack is not calibrated, refer to P C ETVE PRA 501 – Opposition method jack

calibration for on site calibration of the jack.

DETERMINATION OF THE FINAL PRESSURE P0 The final pressure in the jack is obtained by the following calculation:

( )( ) )1(1 321

0

KKKS

FP

tension

O−⋅+−

=

Where P0 [bar] Final pressure in the jack

F0 [daN] Force in the tendon under the anchorage at the stressing stage

Stension [cm²] Section of the jack tensioning chamber

K3 [%] Friction losses

Note: If the designer provides stress data, the force F0 is first calculated as follows:

strandSnF ..00 σ=

Where σ0 [MPa] Stress in the tendon under the anchorage

Sstrand [mm²] Section of a strand

n Number of strands in the tendon





REV. DETERMINATION OF THE FINAL ELONGATION TO OBSERVE ON STRAND

The strand elongation is usually calculated by the designer for the whole tensioning

operation. On site, part of this elongation will be done during the first stage stressing, and

the rest during the final stressing.

Elongation is not controlled during the first stage stressing.

During the final tension, the elongation measured (∆0) corresponds to the elongation of the

strands between 0.25 P0 (first stage stressing final pressure) and P0 (final tension final

pressure), which is linked to the theoretical elongation with the following relation:

∆0 = A – 0

0

P

P0.25A ⋅×

Where ∆0 [mm] Elongation to observe at the end of the tensioning operation

A [mm] Tendon theoretical elongation

3

JAW PULL-IN AFTER LOCKING-OFF

To calculate the wedge pull-in (net pull-in), the pull-in read on the strand (or jack)

movement (gross pull-in) must be corrected to take into account the elastic shortening of

the strand length between the anchorage wedge and the jack wedge.

The reading of the gross pull-in is taken between the tensioning final pressure stage and the

50 bar releasing stage (after blocking the jaws). This correction, calculated for a jack

opened at 80% of its tensioning stroke and a strand stressed at 90% of yield strength is :

Net pull-in = Gross pull-in - Correction

The correction depending on the jack used and the stroke is given in the following table :

Wedge Pull-in Correction (mm) Jack Read from index

on piston of jack

Read from index

fixed on strand

SC2-180 6 4

SC2-600 10 8

SC2-1000 13 11

U24 9 7

TITAN 25 7 5

IHS 25T-150 6 4

IHS 25T-610 10 8

Example: For a SC2-180 jack, if the gross pull-in is 12 mm read from graduated

piston : The net pull-in is = 12 – 6 = 6 mm.





REV.

Appendix 2: Tensioning record sheet

PREPARATION OF THE TENSIONING RECORD SHEETS The following information must be given on the tensioning record sheets:

� The name of the structure or element,

� The reference number of the tendon,

� The type of tendon,

� The type of jack used,

� The references of the tensioning equipment: jack(s), pump(s) and pressure

gauge(s),

� The name of the PT supervisor,

� The final pressure – P0,

� The wedges locking-off pressure,

� The final theoretical elongation - ∆0,

� The elongation tolerance at the final stage [0.95 ∆0; 1.10 ∆0],

� The correction for the calculation of the net pull-in (jaw pull-in).

It is mandatory that a record sheet is prepared for each tendon.

Note: The elongation tolerances given above comply with the requirements of French

regulations; however, they must be adjusted to meet the applicable local regulations.





REV.

TENSIONING RECORD SHEET C

Date :

Localisation : Phase n° Tendon n°

WP n° ITP n° ICL n°

Drawings

Coil n° Strand n° Coil n° Strand n° Coil n° Strand n°

OPERATORBlock lot n° Jack n° Name :

Signature :

Anchorage block centering on trumplate (guide) before, during

and after strand stressing:

Before During After

Gross pull-in Correction Net Pull-in Dinitial Dfinal Dfinal-Dinitial

� [mm] � [mm] � -� [mm] [mm] [mm]

Observations during final tensioning : Elongation criterion:

YES / NO

1.10 ∆0 =

YES / NO

YES / NO

YES / NO

YES / NO

0.95 ∆0 < Dfinal-Dinitial < 1.10 ∆0

[bar]

Documents of reference

Technical characteristics

Tendon unit

Bobines / Torons

EndMATERIEL

Extremity �

Checking horizontally

Checking vertically

Jack Type

CIVIL WORK - RECORD SHEET TRS N° :

PRESTRESSING WORK

TENSIONING RECORD SHEET

EQUIPMENT

Jaws lot n° Manometre n°

Extremity �

[bar]

First stage stressing(25% of the final force)

0.95 ∆0 =

FREYSSINET CONTRACTOR

2

1

First stage theoretical pressure PP (bar):

Final pressure P0

OTHERS

Final stressing theoretical final pressure P0 (bar):

∆0 =

Checked by : Approved by : Noted by :

Date : Date : Date :

Signature : Signature : Signature :

Strand

1

2

3

4

5

Elongation

correct ?

Final stressing

Locking-off /

Observations

3

4

5

Locking-off / ObservationsStrandPressure PP





REV. Appendix 3: STRAND TENSIONING EQUIPMENT

TENSIONING JACK Tensioning operation is made with monostrand jack : SC2 jack with a stroke of 180, 600 or

1 000 mm, U24 jack, TITAN 25 jack or IHS 25T jacks can be used, depending on the case

and availability.

The jack must be equipped with an adaptation nose fitted with the type of anchorage to

tension. For each model of jack, two different types of nose exist: for B13 anchorages, and

for B15 anchorages.

The minimum and normal overlengths depend on the jack used, and are given in the table

below.

Jack Minimum overlength

(mm)

SC2-180 350

SC2-600 350

SC2-1000 350

U24 650

TITAN 25 350

IHS 25T-150 350

IHS 25T-610 350

The elongation of the strand overlength during the tensioning operation is given in the

table below for each type of jack. These corrections are calculated for a jack open at 80%

of its tensioning stroke and a strand stressed at 90% yield strength.

Jack Elongation of the

overlength (mm)

SC2-180 4

SC2-600 8

SC2-1000 11

U24 7

TITAN 25 5

IHS 25T-150 4

IHS 25T-610 8





REV.

TENSIONING PUMP

� 1 hydraulic pump equipped with pressure gauges.

� Hoses fitted with valves.

Pumps with low output at high pressure such as SP20 and POWER TEAM PE 554 are well

fitted for tensioning operations with monostrand jacks.

Note: Pressure gauges used are generally 0-1000 bar. When P0 is less than 450 bar, it is

preferable to use a 0-600 bar pressure gauge in the tensioning circuit, that will make the

measurements accurate.