3.fiber reinforced plastics
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FIBER REINFORCED PLASTICS (SFRPs) for REPAIR and
STRENGTHENING of CONCRETE BRIDGE STRUCTURES AN
ANALYSISBy
Prof. Cristina T. Coquilla of Adamson University, Philippines
Prof. Junichiro Niwa of Tokyo Institute of Technology
The Problem and Its Background
Damage to concrete bridges may not only be of a material or structural
nature but may have adverse effects on the aesthetic appearance. Whereas it
should be sought to repair the structure in the most effective manner, care
should be taken that the method of repair does not aggravate the situation.
Where upgrading is involved, this may pose a major problem and great ingenuity
may be necessary in some cases to apply strengthening systems that do not
deface the overall aesthetic appearance.
Due to the difficulty and cost involved in strengthening an existing
concrete bridge to new design standards, it is usually not economically justifiable
to do so. Therefore, the goal of this study is often limited to preventing
unacceptable failure. This means that a considerable amount of a structural
damaged during a major earthquake is acceptable provided collapse of the
bridge is prevented. In the case of major concrete bridges, the ability of the
bridge to carry emergency traffic immediately following an earthquake may
require a higher level of performance with less structural damage, the threshold
of damage that will constitute unacceptable failure must therefore be defined by
the engineer by taking into consideration the over-all configuration of the
structure, the importance of the structure as a lifeline following a major
earthquake, the case with which certain types of damage can be quickly repaired,and the relationships of the bridge to other structures that may or may not be
affected during the same earthquake.
It should be noted that cost is also a major issue. Therefore, a
mobilization and traffic control costs represent a major part of the total seismic
repair cost.
Reinforcing fibers will stretch more than concrete under loading.
Therefore, the composite system of fiber reinforced concrete is assumed to work
as if it were unreinforced until it reaches its first crack strength. It is from thispoint that the fiber reinforcing takes over and holds the concrete together.
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For fibers reinforcing, The maximum load carrying capacity is controlled
by fibers pulling out of the composite because fiber reinforcing does not have a
deformed surface like larger steel reinforcing bars. This condition limitsperformance to a point far less than the yield strength of the fiber itself. This is
important because some fibers are more slippery than others when used as
reinforcing and will affect the toughness of the concrete product in which they
are placed.
Toughness is based on the total energy absorbed prior to compete
failure.
It is from this theory, that the authors conducted a research on the repair
of concrete bridges using sprayed fiber reinforced plastics.
In this study, a new, inexpensive, and simple strengthening method for
concrete structures is discussed and suggested in order to improve future
seismic strengthening. This method, using short fibers with vinyl ester, is a new
combination of materials as seismic strengthening. Chopped short fibers of
carbon and glass with vinyl ester/polyester resin are sprayed in place on the
concrete structures. It is called Sprayed Up FRP (Fiber Reinforced Polymer).
The benefit of using vinyl ester resin in this strengthening method is that it takes
shorter time to harden the resin than where epoxy resin is used. In addition, the
mechanical properties of vinyl ester resin are the same as the one of epoxy
resin.
Statement of Purpose:
This research contains procedures for evaluating and upgrading the
seismic resistance of existing highway concrete bridges. Specifically it contains
h the design requirements of the Sprayed Fiber Reinforced Plastics
for increasing the seismic resistance of existing concretebridges.
h to minimize the risk of unacceptable damage during a
design earthquake. Damage is unacceptable if it results in:
the loss of life
the collapse of all or part of the bridge
the loss of use of a vital transportation route
h to investigate the effect of SFRP strengthening to ReinforcedConcrete (RC) member with deterioration such as crack andcorrosion of steel bars.
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h to propose the calculating way of load carrying capacity of RC
member with SFRP
hto improve the peel off of SFRP improve the transformability of SFRP
using the resin that has larger extensibility to strain
using resin that has lower strength
improve the bonding strength
using the uncongealer (rough surface)
using the concrete spike( fix SFRP at some points)
Scope and Delimitations:
This research is intended for use on highway concrete bridges of
conventional steel and concrete girder and box girder construction with spans
not exceeding 500 feet (150 meters). Suspension Bridges, cable-stayed bridges,
arches, and movable bridges are not covered. However, many of the concepts
presented here can be applied to these types of structures if appropriate
judgment is used. Although specifically developed for highway bridges, this
research may also have applicability to other type of bridges. Minimum
requirements for evaluation and upgrading will vary based on SPC (Seismic
Performance Category).
Related Literature:
Portland Cement Concrete is considered to be a relatively brittle material.
When subjected to tensile stress, unreinforced concrete will crack and fail. Since
the mid 1800s steel reinforcing has been used to overcome this problem. As a
composite system , the reinforcing steel is assumed to carry all tensile loads.
Placing an external reinforcement on a structure is a common practice
either to improve its performance during an earthquake or to repair it after anearthquake. This can be used also for under-designed structure. The materials
can be of reinforcement consisted either of concrete materials placed by
spraying or coating and/or steel plate or jackets bounded. However, the
materials needed to develop is a lightweight, high strength materials with
superior durability and corrosion resistance that can also be applied with relative
case to take place in. The use of fiber-reinforced polymers (FRPs) fulfills that
need. Polymers and fibers can be combined in a material to suit the specific
needs of a structure.FRP carrying continuous fiber is that they are highly anisotropic.
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Properties in the direction of fiber alignment , such as tensile strength, elastic
modulus and the thermal stability are far superior to those in the direction
perpendicular to fiber alignment. In addition, continuous fiber composite areessentially brittle and show poor toughness both in the direction of the fiber and
perpendicular to it.
Vinyl Ester Resins are known for their chemical resistance, excellent
wetting, toughness and high temperature properties for composite parts. It is a
resin consisting of an epoxy backbone, for chemical resistance and high strength,
combined with vinyl groups, for high reactivity, and styrene monomer, for low
viscosity. The vinyl groups (carbon to carbon double bonds) and ester linkages
are only at the ends of the resin molecule. This controls the cross linking density,
providing flexibility to the resin matrix. Also these groups are less likely to remain
unreacted in the composite, providing less sites for chemical attack. The ester
linkages are adjacent to methyl groups, making them less susceptible to
breakdown through hydrolysis. These resins are used in composites for
corrosion resistant applications.
Fiber Reinforced Plastics are low weight, high strength, ease of erection,
and corrosion resistance. These factors combined lead to lower installation costs
and lower maintenance costs. When the manufacturing process is perfect and
the standards have been developed, the initial costs may be lower as well. All of
these factors could lead to lower-life cycle costs than using traditional materials.
Nowadays, strengthening by post casting concrete, steel plate jacketing,
fiber reinforcement such as carbon, aramid, and glass are utilized as seismic
strengthening methods for concrete structures. Recently, a seismic
strengthening method by wrapping continuous fiber sheets has often been used,
since the constructibility and durability is superior. However, materials using
continuous fiber are expensive. On the spread of seismic strengthening for
buildings and infrastructures in the future, simple methods of strengthening withlow cost should not only be suggested, but also seismic behaviors should be
cleared.
Definition of Terms:
Glass Fiber is manufactured by Owens Corning, has a diameter of 11 microns,
a tensile strength of 3400 Mpa, an elastic modulus of 81 Gpa, and
elongation at break of 4.6%. It has a high performance , silane-based
sizing that is applied to fiber filaments to improve handling and optimizethe fiber-resin bond in the composite.
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Vinyl Ester Resin(R802)- consisting of an epoxy backbone, for
chemical resistance and high strength, combined with vinyl groups, for high
reactivity, and styrene monomer, for low viscosity. The vinyl groups (carbon tocarbon double bonds) and ester linkages are only at the ends of the resin
molecule. This controls the cross-linking density, providing flexibility to the resin
matrix. Also these groups are less likely to remain unreacted in the composite,
providing less sites for chemical attack. The ester linkages are adjacent to
methyl groups, making them less susceptible to breakdown through hydrolysis.
These resins are used in the composites for corrosion resistant applications.
Vinyl Ester Resin R806- a special type of Vinyl ester resin and they
have the same purpose of R802 as a polymer.
Polyester Resins- are homopolymers based on p-oxybenzol repeat
units and are linear thermoplastics. They are highly crystalline polymers but
have no observed melting point even at up to 900 to 1000 degrees Farenheit.
Flow and creep are virtually non-existant below their crystal translation
temperature of 625 degrees. Polyester has a density of 1.44 gm/cc. Polyester
possess a compressive strength of 15,000 psi. The high strength results is an
excellent load bearing capacity. Polyester has a thermal conductivity of 3.9
BTU/hr./ft2 /degrees ft/in. Its coefficient of thermal expansion (3.3x10-5
in/in/degrees F) is approximately linear from room temperature to 575 degrees F.
Polyester is a very thermally stable wholly aromatic polymers.
Methodology:
Spraying of fiber reinforced concrete plastics (SFRP) is conducted by
the Vantec Laboratory through the help of Fuji P.S. Testing is done at Tokyo
Institute of Technology. The tensile strength, bending capacity, shearing capacity
and the bond stress are done using samples of concrete with and without SFRP.
The key element of the spray equipment is the nozzle unit that injects thecatalyzed polymer of the spray stream. Attached to the nozzle is a fiber chopper
unit that cuts the incoming fiber strand to various length (13,26,52 mm.) and
injects it in the spray stream along with the catalyzed polymers(see Fig. 1 to 4).
Before applying the spray, the surfaced concrete is coated with a layer of
bonding agent (vinyl ester resin combined with catalyst methyl ethyl keytone
peroxide (MEKP). The polymetric matrix and the fiber are simultaneously
sprayed at a high speed on the surface of a concrete structured to be repaired
(see Fig.5 to 6). The sprayed composite is compacted pneumatically on theapplication surface, and is then finish with a roller (see Fig. 7 to 8) The length of
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the fiber can be adjusted in the process along with the type of polymer and the
sprayed thickness. In this study, we use three (3) types of polymers namely,
Vinyl ester resin, Vinyl ester resin (R806), 50% Vinyl ester resin (R806) and 50%polyester resin (bb 100) and the polyester resin (bb 100).
Figure 1. Spray machine
To spraying gun
Resin tank
Conpression air
Spray machine
Rolling cutter
1/4inch(6mm)
Figure 2. Fiber gun
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Figure 3. The structure of spraying gun
Resin gun
Glass fiber
Cutting andspraying part
Figure 4. Roller (to drive out the air)
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Figure 5. Spraying situation 1
resinGlass fiber
Mixed in the air
Figure 6 Spraying situation (2)
FFiibbeerrss aarree jjuummppiinngg oouutt ffrroomm
rreessiinn
We can adjust the angle of fiber nozzle
TThheerree iiss oorrggaanniicc ssoollvveenntt ssmmeellll
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Figure 7 Driving out the air using roller
roller
Figure 8 Driving out the air using roller
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Fig. 12 Beam Bending Test Outline
Fig.14- load displacement curve w/ and w/o spraying of SFRP
B e a m b e n d in g te s t o u t lin e
2 5 0
1 5 0
2 0 0
1 2 0 0
4 7 5 4 7 5
3
CL
1 25
1 00
1 00
S t r a in g a g e
S p r a y i n gs u r f a c e
R e s i n
P e a l o f f
W i re b r u s h i n g& s p i k in gr e t a r d e rC h i p p i n gW ir e b r u s h i n gN o t h i n g
P o l y e s t e r B B - r e s i nV i n y l e s t e rN o n e
T h i s t im eL a s t t im e
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Fig. 15- Load Crack and Crack-Displacement Curve
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Table1-Stresses of the Specimens
Reinforcement arrangement A B C
Diameter of steel bar 15.9 22.2 22.2
Reinforcement ratio (area) 0.794 1.548 2.323
Stirrup diameter (mm) 6.35
Bending capacity (KN) 71.6 132.6 187.9
Shear capacity (KN) 216.2 117.7 134.8Without SFRP
Failure mode Flexural tension Diagonal tension Diagonal tension
Bending capacity (KN) 91.2 1.27 150.4 1.13
Shear capacity (KN) 216.2 117.7
Shape of SFRP
a type
thickness Failure mode Flexural tension Diagonal tension
Bending capacity (KN) 104.0 1.45
Shear capacity (KN) 216.2
Shape of SFRP
a type
thickness 5 Failure mode Flexural tension
Bending capacity (KN) 140.3 1.06 194.4 1.03
Shear capacity (KN) 297.7 2.53 314.8 2.34
Shape of SFRP
b type
thickness Failure mode Flexural tension Flexural tension
Bending capacity (KN) 100 1.40 157.8 1.19 210.1 1.19
Shear capacity (KN) 396.2 1.83 297.7 2.53 314.8 2.34Shape of SFRP
c type
thickness Failure mode Flexural tension Flexural tension Flexural tension
Yielding point of steel bar is 380MPa, and youngs modulus is 200,000MPa
Compressive strength of concrete is 35MPa
Assume SFRP at bottom resist not to the shear but to the bending.
Assume the direction of diagonal tension crack is 45 , and SFRP can resist till it
ruptured in Shape of SFRP b and c
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Figure 18- Spraying thickness of 3.5 mm of 26 mm fiber length
Note: The dimension of specimen sprayed is 100 square mm. with a length of
450 mm. and a reinforced with no. 23 bars
This 3.5 mm. thickness is recommendable. There is no peeling occurs on
the surface.
Figure 19- Spraying thickness is 5mm of 26 mm. fiber length
Note: From Figure 19, you will notice the peel-off of the sprayed fiber from the
specimen.
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stress-strain curve of bb 13
0
10
20
30
40
50
6070
80
0 5000 10000 15000 20000 25000
strain(
stress(M
P
a)
bb13
bb132
bb133
bb134
bb135
stress-strain curve of bb 26
0
10
20
30
40
50
60
70
80
0 5000 10000 15000 20000 25000
strain(
stress(M
P
a)
bb26
bb262
bb263
bb264bb265
stress-strain curve of bb 52
0
10
20
30
40
50
60
70
80
0 5000 10000 15000 20000 25000
strain(
stress(M
P
a)
bb52
bb522
bb523
bb524
bb525
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Figure 17-Stress- Strain Diagram of the different length in Fiber
Note that from figure 17, polyester (bb) with a length of 26 mm will give better
result of stress-strain curve.
stress-strain curve
0
10
20
30
40
50
60
7080
0 5000 10000 15000 20000 25000
strain(
stress(M
P
a)
bb13
bb26
bb52
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shearing test
Table Concrete compressive strengthfc (MPa) ft (MPa)
Design
strength
41.4 3.47
Design
strength
65.5 4.20
Table 3 Bond shearing experimental result
Actual thickness of
SFRP
(mm)
Maximum load
(kN)
Fracture morphology
2mm 1.20 22.70 SFRP rupture
2mm 1.35 19.76 SFRP rupture
3.5mm 1.70 31.35 SFRP rupture
3.5mm 3.20 4.034 SFRP rupture
5mm 5.70 49.65 Peeling
5mm 2.35 40.66 SFRP rupture
5mm 50MPa 4.10 46.06 Peeling
Concrete design strength of 30MPa are used except for 5mm.
Figure 20- Spraying thickness Maximum load relationship
0
10
20
30
40
50
60
0 1 2 3 4 5 6
MaximumloadkN
Actual spraying thicknessmm
PeelingPeeling
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Figure 21- Strain distribution on SFRP surface
0
2000
4000
6000
8000
10000
12000
-100 -50 0 50 100
2mm
0%20%40%80%60%Peakor
()
(mm)Distance from center
2mm
Strain
0
2000
4000
6000
8000
10000
12000
-100 -50 0 50 100
2mm
0%20%40%60%80%Peakor
()
(mm)Distance from center
2mm
Strain
0
2000
4000
6000
8000
10000
12000
-100 -50 0 50 100
3.5mm
0%20%40%60%80%Peakor
()
(mm)Distance from center
3.5mm
Strain
0
2000
4000
6000
8000
10000
12000
-100 -50 0 50 100
3.5mm
0%20%40%60%80%Peakor
()
(mm)Distance from center
3.5mm
Strain
0
2000
4000
6000
8000
10000
12000
-100 -50 0 50 100
5mm
0%20%40%60%80%Peakor
()
(mm)
Distance from center
5mm
Strain
0
2000
4000
6000
8000
10000
12000
-100 -50 0 50 100
5mm
0%20%40%60%80%Peakor
()
(mm)Distance from center
5mm
Strain
0
2000
4000
6000
8000
10000
12000
-100 -50 0 50 100
5mm
0%20%40%60%
80%orPeak
()
(mm)Distance from center
5mm
Strain
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1. Calculation of bond shearing strength
Bond shearing strength is calculated from the following equation.
( )( )
dx
xd
b
Ax
SFRPSFRP
=
Then, we try to calculate the bond shearing strength from the strain distribution of the
specimen which was destroyed by peeling.
Table 4
5mm 5mm Average
Maximum stress
slope
dx
dSFRP
(MPa/mm)1.495 1.475
Cross section ofSFRP
SFRPA (mm2)
420 380
Width of SFRP
b (mm)100 100
Bond shearingstrength
max (MPa)6.28 5.61 5.95
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Figure 28-Load Displacement Curve of type A
0
20
40
60
80
100
120
0 10 20 30 40 50
Displacement (mm.)
Load(KN)
Type A-a5mm
TypeA-a3mm
TypeA(w/oSFRP)
Type Ac-3mm
Figure 29-Load Displacement Curve
0
50
100
150
200
250
0 10 20 30 40
Displacement (mm.)
Load
(KN
)
TypeB(w/oSFRP)
TypeBb3mmTypeBa3mm
TypeBc3mm
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Figure 30-Load Displacement Curve of Type C
0
50
100
150
200
250
0 10 20 30 40
Displacement (mm.)
Load
(KN
)
TypeC(w/oSFRP)
TypeC-b3mm
TypeC-c3mm
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Type A under Compressive Stress
Type A under Tensile Stress
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Type B under Compressive Stress
Type B under Tensile Stress
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Type C under Compressive Stress
Type C under Tensile Stress
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Costing:
For vinyl ester resin, the following are the unit cost:
the unit cost of resin;R806- 750/kg.
R802- 750/kg.
BB100-650/kg.
The unit cost of glass fiber- 220/kg.
The unit cost of SFRP spraying- not yet available
Based from Figure 28,29 and 30, the Load Displacement Curve with SFRP
gives better displacement results than without SFRP, it appears that
specimen with SFRP gives more strength than without Spraying which
shows in the said graph. Comparison of using finite element analysis of
Diana software and the actual experimental value in Figure 31, shows that
the finite element analysis and the experimental values will give almost the
same result.
Conclusions:
1. SFRP spray process of strengthening and rehabilitation is a very promising
technique, and continued research will undoubtedly lead to its use in reality.
2. It appears that SFRP have the potential to significantly increase the strength
of existing concrete structures, while at the same time dramatically improving
their fracture energy characteristics.
3. The results indicate that while a number of issues still remain to be
addressed, the use of SFRP for repair and retrofit has advantages over the
traditional wraps on the basis on ease of placement, labor cost and
workmanship requirements.
4. It is highly recommended for highway concrete bridge repair as a form ofretrofitting.
5. The thickness of spraying is 3.5 mm and the length of fiber is 26 mm. To
avoid peel-off.
Recommendations:
The following are the recommendations for future studies:
1. To investigate the actual cost of the SFRP if it is more economical to use.
2. To investigate its durability characteristics under the Philippine weather.. Try to make another mixing type of SFRP using another resin or combination of
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resins.
3. To determine the ability to withstand elements and other detrimental
influences out there in field.
References:
1. N. Banthia, A. Bentur, A. Mufti, Fiber Reinforced Concrete, The Canadian
Society for Civil Engineers, 1998
2. N. Banthia and S. Mindess, Fiber Reinforced Concrete (Modern
Developments), The University of British Columbia, Vancouver,
Canada,1995
3. Thomas W. Berg Fiber Reinforced Concrete, http://www.retail
source.com/information
4. Sprayed-Up FRP Strengthening for Reinforced Concrete Beams,
http://www.tsukuba.ac.com
5. Fiber Reinforced Concrete, http://www.fibermesh.com
6. Stone Solutions Custom Concrete Countertops,
http://www.stone-solutions.com
7. Cary Concrete Products, Inc. Materials, http://www.caryconcrete.com
8. Durastone, http://www.durastone.com
9. Superior Polymer Products Vinyl Ester Resin Technical Data,
http://www.superiorpolymer.com
10. Composites-What is a Vinyl Ester Resin?, http://www.cabot.corp.com
11.http://www.bouyer.net/digests/2000
12. Polyester Resin, http://www.deq.state.la.us/assistance
13. Polyester Resin, http://www.sculpt.com/catalog_98
14. Rule 1162- Polyester Resin Operations, http://www.aqnd.gov/rules/htm
15. Polyester Resin Plastics Products Fabrication,
http://www.dep.state.fl.u/air/permitting/plastics.htm16. 4684-1 Rule 4684 Polyester Resin Operations (Adopted May 19,.),
http://www.valleyair.org/rules/currentrules
Diana Finite Element Analysis, TNO Building and Construction Research, 2000
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ABOUT THE AUTHOR
Engr. Cristina Tanhueco-Coquilla is at present the Chairperson of the Civil
Engineering Department of Adamson University. She earned her Master ofEngineering, major in Civil Engineering from Technological University of the
Philippines and her B.S. Degree in Civil Engineering from the University of the
East. She was at one time also the Chairperson of the Civil Engineering
Department of the University of the East. At present she is taking up Ph.D. in
Technology Management at the Technological University of the Philippines. She
may be contacted at 14 Rd. 7 G.S.I.S. Hills Talipapa, Novaliches, Tel. No.
(02)983-11-41, Cell/Text No. 0917-240-6529, E-mail Address:
ccoquilla@adamson.edu.ph, cristinacoquilla@yahoo.com.
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