c3- sika stresshead
TRANSCRIPT
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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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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