c3- sika stresshead

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Sika StressHead

Prestressed CarboDur CFRP Plate System

System Information

Zürich, April 2002


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Table of Contents

1 The Sika-StressHead System ............................................................................... 11.1 System Components .................................................................................. 1

1.2 Sika-StressHead Structure .......................................................................... 2

1.3 Anchorage ................................................................................................ 2

1.4 Prestressed CarboDur CFRP plate............................................................... 4

2 Laboratory Tests................................................................................................. 6

2.1 Short time tensile test ................................................................................. 6

2.2 Long time tensile test.................................................................................. 8

2.3 Fatigue test ............................................................................................... 9

3 Application of the Sika-StressHead-System ............................................................ 93.1 Function of the applied System .................................................................... 9

3.2 Range of Application ................................................................................ 10

4 Implementation process ..................................................................................... 11

4.1 Design.................................................................................................... 11

4.2 Fabrication of the system .......................................................................... 12

4.3 Application of the System.......................................................................... 12


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Sika-StressHead System Technical System Information Page 1

1 The Sika-StressHead System

The Sika-StressHead-System is a system for an efficient strengthening of structures with

prestressed CarboDur CFRP plate.

The system uses CFRP products, which have excellent properties due to tensile resistance,

corrosion, weight, and required additional space to place the system.

1.1 System Components

The Sika-StressHead-System is composed of 3 main elements:

1. Concrete Structure

StressHead

Anchorage

CarboDur plate

Force introduction

Prestressing jack

2. Anchorage, which transmits the prestress-force from the CarboDur plate into the

Structure

StressHead

Anchorage

CarboDur plate

Force introduction

Prestressing jack


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3. CarboDur CFRP plate, which is prestressed on site

StressHead

Anchorage

CarboDur plate

Force introduction

Prestressing jack

1.2 Sika-StressHead Structure

The Sika-StressHead-System allows minimal requirement on the structure, which has to be

improved in terms of serviceability and or reinforcement, since:

1. no adhesive is needed between the structure and the laminate to transmit the

prestress-force. The Sika-StressHead-System transmits forces over the end-

anchorage.

2. minimal interference with the existing structure due to the anchorage system

3. little additional space needed to place the anchorage at the existing structure

1.3 Anchorage

Transversal Beam

The anchorage transmits the force from the CFRP Head into the concrete structure. The

CFRP Head is supported by a slat transversal beam. This beam is shifted over the CarboDur CFRP plate. The force is transmitted from the beam over two threaded bolts to the


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anchorage shoe.

Transversal Beam

Anchorage shoe for transmission of prestressing

The anchorage shoe is made out of steel same as the transversal beam. The two load

bearing threaded bolts are fixed to the shoe. The force is introduced into the concrete

structure over a tube placed into a drilled whole.

The shoe is stabilized against the overturning moment due to the eccentricity and aligns

itself under load without any secondary effects.

The prestress machine can be placed on the shoe to pull back the two threaded bolts

connected to the Transversal Beam and the CFRP Head. The bolts can be fixed in the pulled

back position after tensioning over washers to the shoe.

Adaptations of the anchorage systems due to special situations are possible.

Anchorage shoe

Mounted anchorage system:

StressHead = CFRP Head


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1.4 Prestressed CarboDur CFRP plate

The CarboDur CFRP plate is very light and flexible and consists out of two parts:

1. CarboDur CFRP plate

2. CFRP Head = StressHead

CarboDur CFRP plateThe Sika CarboDur CFRP plate is a S624 type.

CFRP plate properties:

Section 60 mm * 2,4 mm = 144 mm2

Tensile strength f tk = 2’800 N/mm2

Ultimate strain u = 1,7 %

E-Modulus E = 165 kN/mm2

CFRP Head (StressHead)

The CFRP Head is placed at the end of the laminates, where the concentrated prestressing

force is transmitted to the anchorage shoe. The Head was developed to have an efficient

level in terms of exploiting the tensile resistance of the laminate.

The Tendon was tested and improved according to the internationally acknowledged

institution EOTA, European Organisation for technical Approvals (Guidelines for European

technical approval of Post-tensioning kits for prestressing of structures) at the Swiss Federal

Institute of Technology (ETHZ) in Zurich.


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Information for Designers:

Prestressing force P0 = 220 kN

Stress in CarboDur plate P0 = 1’540 N/mm2

(0,55 f tk)

Corresponding strain P0 = 0,95 %Minimal tensile strength in the CFRP Head Pd = 350 kN

Corresponding minimal tensile

stress

CFRP Head = StressHead


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2 Laboratory Tests

2.1 Short time tensile test

Test procedure

The test tendon consists of a CarboDur CFRP plate of 2m length with a CFRP Head (Stress

Head) at one side. The CFRP Head is supported by a transversal beam similar to the one of

the anchor system. This beam is connected to the test machine.

On the other side the laminate is directly connected to the test machine.

CarboDur 60x2.4mm

u1u2

u3StressHead

Strain gauge 1train gauge 2

2 0 0 0 m

m


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The test tendon is loaded with a centric tensile force. The load application is controlled over

the displacement.

1. sequence of the test: tensile load is applied up to 0,65 f tk ( = 1820 kN/mm2) and held

stagnant for 2 hours.

2. sequence of the test: after a relief down to 10 % of the tensile strength of the

laminate the test tendon is loaded to the breaking point

0 20 40 60 80 100 120 140 160

0

500

1000

1500

2000

2500

S t r e s s / M P a

2 hours

2000

mi

-11820 MPa = 0.65 f tk

280 MPa = 0.1 f tk

0.6000mi

-1

0.6

0/00

mi-1

Failure

Time in minutes

Parameters to be measured

Displacement of the piston of the test machine

Force applied by the test machine

Displacement inside the CFRP Head

Displacement between the CarboDur plate and the CFRP Head

Strain of the CarboDur plates


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Requirements on the performance

In a series of 3 test tendons none should break below the break load of 0,75 f tk

(2100 N/mm2). Test results show no problems in performing along the sat requirements.

Test Conclusion

The requirements were met in the executed tests. The system showed a constant behaviour.

2.2 Long time tensile test

Test procedure

The test tendon consists of a CarboDur CFRP plate with one CFRP Head on each side. The

plate has a length of 1,8 m.

Two transversal beams support the CFRP Heads. This beams are connected over threaded

bolts to a steel profile HEB 300. The tendons is stretched and then fixed over the bolts to the

steel profile. The test tendon stays under the constant displacement 3 to 6 months.

1800 mm

HEB 300StressHead

Parameters to be measured

Force applied by the test machine

Displacement inside the CFRP Head

Displacement between the CarboDur plate and the CFRP Head (slip)

Strain of the CarboDur plates


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Test Conclusion

Pre-tests and measurements on already applied systems show no relaxation of the system.

2.3 Fatigue test

Test procedure

A break down of the tendon due to fatigue must not be expected for real vibration

frequencies and amplitudes on concrete structures. The test will show possible displacement

(slip) between StressHead and CarboDur plate due to cyclic loads.

The test tendon is the same as it is described for the short time tensile load test.

The load applied for the test:

Low tension u = 1540 N/mm2(0,55 f tk = Prestress-force)

High tension o = 1740 N/mm2

Tension Amplitude = 200 N/mm2

Number of cycles 157’000

Frequency appr. 1 Hz

Test Conclusion

First tests show no additional slip in the tendon due to cyclic loads.

3 Application of the Sika-StressHead-System

3.1 Function of the applied System

The Sika-StressHead-System can be used for both:

1. Strengthening of structures

2. Improvement of the serviceability of strengthened structures

The function of the system is based on the function of external none bonded prestress-

systems. In this systems a positive acting external load (prestress force) is introduced into

the structure to relieve it.


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With this relieve loads can be carried with enough security and a better performance due to

serviceability.

The relieve of the supporting structure will reduce deformations and crack-widths in concrete

structures.

Since the system works totally different compared to the commonly used not prestressed

bonded CarboDur CFRP plates to reinforce concrete structures a detailed analysis must be

made.

Advantages in terms of static security and serviceability:

Little interference with the existing structure

High efficiency in exploiting the tensile resistance of the CarboDur / High level

of prestress-force

Definite and controlled permanent transmission of the prestress-force

3.2 Range of Application

The system can be applied basically in all structures in combination with different materials.

So far it was used mainly with concrete structures for bridges and building.

Advantages in terms of the implementation and the construction:

Little additional weight on the structure

No corrosion of the tendon possible

Little requirements on quality of the existing structure

Little space needed to place the anchorage

Flexible system to meet any specific conditions for construction (bending with

little radius are possible)

Easy, fast and slender application


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4 Implementation process

The implementation of the system can be divided in 3 part-processes. Over these processes

a quality control system will guarantee the correct application.

1. Process: Design

2. Process: Fabrication of the System

3. Process: Application of the system

4.1 Design

Properties of the systemThe system is designed according to the prestress system codes, where the weakest

element is the tendon and not the anchorage.

Applying the system the capacity for deformation of the structure is not impaired. The break

down of the system occurs when the reinforcement steel in the concrete structure yields.

The ductility of the structure is maintained.

This is due to the capacity of an additional displacement of 0,33% to the prestress level.

Static Verification

The verification of the reinforced structure follows the rules according to the international and

the national codes for external prestress- systems with no bond. The prestress-force is put

into calculation as an active force on the load side.

To define the permanent prestress-force P the following effects and impacts have to be

taken into account:

Relaxation of the CarboDur CFRP plate

Creeping of the structure (concrete)

Creeping of the anchorage

Slip in the CFRP Head

Impact of changing temperature

Impact of burning


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4.2 Fabrication of the system

1. All CFRP elements, the laminates and the elements of the head are produced in

series.

2. The Tendon is produced by cutting the exact length of the laminate according to the

project and mounting the two heads in the factory.

3. Before sending the tendon to the site it is prestressed in the factory to a level 10%

higher than the admitted prestress level.

4. The anchorage after the shown standard solution can be delivered with the tendon.

Adaptations are possible.

4.3 Application of the System

The application of the system is composed by following steps:

See next page


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1 Po + 10 % Quality control in factory

2 Search existing reinforcement

3 Drill anchoring hole for anchorage

4 Applicate the stressing anchorage

5 Applicate the fix anchorage


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6 Prepare the CarboDur CFRP plate

7 Applicate the SIKA-StressHead-System

into the fix anchorage

8 Applicate the SIKA-StressHead-System

into the stressing anchorage

9 Prestress the SIKA-StressHead-System

c3- sika stresshead

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