STRENGTHENING
STRUCTURES USING FRP
COMPOSITE MATERIALS
DAMIAN I. KACHLAKEV, Ph.D., P.E.
California Polytechnic State University
San Luis Obispo
WHY COMPOSITES?
• ADVANTAGES OVER TRADITIONAL
MATERIALS
• CORROSION RESISTANCE
• HIGH STRENGTH TO WEIGHT RATIO
• LOW MAINTENANCE
• EXTENDED SERVICE LIFE
• DESIGN FLEXIBILITY
COMPOSITES DEFINITION
• A combination of two or more materials (reinforcement,
resin, filler, etc.), differing in form or composition on a
macroscale. The constituents retain their identities, i.e..,
they do not dissolve or merge into each other, although
they act in concert. Normally, the components can be
physically identified and exhibit an interface between
each other.
DEFINITION
Fiber Reinforced Polymer (FRP) Composites
are defined as:
“A matrix of polymeric material that is
reinforced by fibers or other reinforcing
material”
COMPOSITES MARKETS
•
•
•
•
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•
•
TRANSPORTATION
CONSTRUCTION
MARINE
CORROSION-RESISTANT
CONSUMER
ELECTRICAL/ELECTRONIC
APPLIANCES/BUSINESS
AIRCRAFT/DEFENSE
U.S. COMPOSITES SHIPMENTS - 1996 MARKET SHARE
SEMI-ANNUAL STATISTICAL REPORT - AUGUST 26, 1996
Aircraft/Aerospace
0.7%
Transportation
30.6%
Construction
20%
Other- 3.4%
Consumer
Products - 6%
Marine - 11.6%
Electrical/
Electronic - 10%
Corrosion-Resistant
Equipment - 12.4%
Includes reinforced thermoset and thermoplastic
resin composites, reinforcements and
fillers.
Appliance/Business
Equipment - 5.3%
SOURCE: SPI Composites Institute
Infrastructure Benefits
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HIGH STRENGTH/WEIGHT RATIO
ORIENTATED STRENGTH
DESIGN FLEXIBILITY
LIGHTWEIGHT
CORROSION RESISTANCE
LOW MAINTENANCE/LONG-TERM DURABILITY
LARGE PART SIZE POSSIBLE
TAILORED AESTHETIC APPEARANCE
DIMENSIONAL STABILITY
LOW THERMAL CONDUCTIVITY
LOW INSTALLED COSTS
FRP COMPOSITE
CONSTITUENTS
• RESINS (POLYMERS)
• REINFORCEMENTS
• FILLERS
• ADDITIVES
MATERIALS: RESINS
• PRIMARY FUNCTION:
“TO TRANSFER STRESS BETWEEN REINFORCING
FIBERS AND TO PROTECT THEM FROM
MECHANICAL AND ENVIRONMENTAL DAMAGE”
• TYPES:
– THERMOSET
– THERMOPLASTIC
RESINS
• THERMOSET
– POLYESTER
– VINYL ESTER
– EPOXY
– PHENOLIC
– POLYURETHANE
RESINS
• THERMOPLASTIC
– ACETAL
– ACRYRONITRILE BUTADIENE STYRENE
(ABS)
– NYLON
– POLYETHYLENE (PE)
– POLYPROPYLENE (PP)
– POLYETHYLENE TEREPHTHALATE (PET)
RESINS
• THERMOSET ADVANTAGES
– THERMAL STABILITY
– CHEMICAL RESISTANCE
– REDUCED CREEP AND STRESS RELAXATION
– LOW VISCOSITY- EXCELLENT FOR FIBER
ORIENTATION
– COMMON MATERIAL WITH FABRICATORS
RESINS
• THERMOPLASTIC ADVANTAGES
– ROOM TEMPERATURE MATERIAL STORAGE
– RAPID, LOW COST FORMING
– REFORMABLE
– FORMING PRESSURES AND TEMPERATURES
POLYESTERS
•
•
•
•
LOW COST
EXTREME PROCESSING VERSATILITY
LONG HISTORY OF PERFORMANCE
MAJOR USES:
– Transportation
– Construction
– Marine
VINYL ESTER
• SIMILAR TO POLYESTER
• EXCELLENT MECHANICAL & FATIGUE
PROPERTIES
• EXCELLENT CHEMICAL RESISTANCE
• MAJOR USES:
– Corrosion Applications - Pipes, Tanks, & Ducts
EPOXY
•
•
•
•
•
EXCELLENT MECHANICAL PROPERTIES
GOOD FATIGUE RESISTANCE
LOW SHRINKAGE
GOOD HEAT AND CHEMICAL RESISTANCE
MAJOR USES:
– FRP Strengthening Systems
– FRP Rebars
– FRP Stay-in-Place Forms
PHENOLICS
•
•
•
•
EXCELLENT FIRE RETARDANCE
LOW SMOKE & TOXICITY EMISSIONS
HIGH STRENGTH AT HIGH TEMPERATURES
MAJOR USES:
– Mass Transit - Fire Resistance & High
Temperature
– Ducting
POLYURETHANE
• TOUGH
• GOOD IMPACT RESISTANCE
• GOOD SURFACE QUALITY
• MAJOR USES:
– Bumper Beams, Automotive Panels
SUMMARY: POLYMERS
• WIDE VARIETY AVAILABLE
• SELECTION BASED ON:
– PHYSICAL AND MECHANICAL PROPERTIES
OF PRODUCT
– FABRICATION PROCESS REQUIREMENTS
Physical Properties of Thermosetting
Resins Used in Structural
Composites
Resin
Type
Density Tensile Elong. ELong.
(kg/m3) Str.
(%) Mod. Term
(MPa)
(GPa) t ,(C)
Polyester
1.2
50-65
2-3
3
120
Vinyl
Ester
1.15
70-80
4-6
3.5
140
Epoxy
1.1-1.4
50-90
2-8
3
120200
Phenolic
1.2
40-50
1-2
3
120150
MATERIAL: FIBER
REINFORCEMENTS
• PRIMARY FUNCTION:
“CARRY LOAD ALONG THE LENGTH OF THE
FIBER, PROVIDES STRENGTH AND OR STIFFNESS
IN ONE DIRECTION”
• CAN BE ORIENTED TO PROVIDE PROPERTIES IN
DIRECTIONS OF PRIMARY LOADS
REINFORCEMENTS
• NATURAL
• MAN-MADE
• MANY VARIETIES COMMERCIALLY AVAILABLE
MAN-MADE FIBERS
•
•
•
•
•
•
•
•
ARAMID
BORON
CARBON/GRAPHITE
GLASS
NYLON
POLYESTER
POLYETHYLENE
POLYPROPYLENE
FIBER PROPERTIES
DENSITY (g/cm3)
Steel
8
Alum
2.76
E-Glass
1.99
S-Glass
1.99
Carbon
1.59
Aramid
1.38
0
2
4
6
8
10
FIBER PROPERTIES
TENSILE STRENGTH
Alum
20
Steel
60
S-Glass
625
Carbon
530
Aramid
525
E-Glass
500
0
200
400
x103 psi
600
800
FIBER PROPERTIES
STRAIN TO FAILURE
Alum
0.2
Steel
0.16
S-Glass
5
E-Glass
4.8
Aramid
2.8
Carbon
1.4
0
1
2
(%)
3
4
5
6
FIBER PROPERTIES
TENSILE MODULUS
Alum
10
Steel
29
Carbon
33.5
Aramid
19
S-Glass
12.6
E-Glass
10.5
0
10
106 psi
20
30
40
FIBER PROPERTIES
CTE - Longitudinal
14
12.6
12
10
8
x10-6/0C
6.5
5
6
2.9
4
2
0.5
0
-2
Aramid
-2
Carbon
S-Glass
E-Glass
Steel
Alum
FIBER PROPERTIES
THERMAL CONDUCTIVITY
1500
1600
1400
1200
1000
x10-6/0C 800
600
400
200
1.5
115
7.5
0
FRP
Steel
BTU-in/hr-ft2 - 0F
Alum
Concrete
FIBER REINFORCEMENT
• GLASS (E-GLASS)
– MOST COMMON FIBER USED
– HIGH STRENGTH
– GOOD WATER RESISTANCE
– GOOD ELECTRIC INSULATING PROPERTIES
– LOW STIFFNESS
GLASS TYPES
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•
•
•
•
E-GLASS
S-GLASS
C-GLASS
ECR-GLASS
AR-GLASS
FIBER REINFORCEMENT
• ARAMID (KEVLAR)
– SUPERIOR RESISTANCE TO DAMAGE
(ENERGY ABSORBER)
– GOOD IN TENSION APPLICATIONS (CABLES,
TENDONS)
– MODERATE STIFFNESS
– MORE EXPENSIVE THAN GLASS
FIBER REINFORCEMENT
• CARBON
– GOOD MODULUS AT HIGH TEMPERATURES
– EXCELLENT STIFFNESS
– MORE EXPENSIVE THAN GLASS
– BRITTLE
– LOW ELECTRIC INSULATING PROPERTIES
TYPICAL PROPERTIES OF
STRUCTURAL FIBERS
Fiber
Type
Density
(kg/m3)
Tensile
Strength
(GPa)
1.72-3.45
Elong.
(%)
2.54
EModulus
(GPa)
72.5
E-Glass
S-Glass
2.49
87
2.53-4.48
2.9
Kevlar 29
1.45
85
2.27-3.80
2.8
Kevlar 49
1.45
117
2.27-3.80
1.8
Carbon
(HS)
Carbon
(HM)
Carbon
(UHM)
1.80
227
2.80-5.10
1.1
1.80-1.86
370
1.80
0.5
1.86-2.10
350-520
1.00-1.75
0.2
2.5
ADVANTAGES AND
DISADVANTAGES OF
REINFORCING FIBERS
Fiber Type
Advantages
E-Glass, S-Glass High Strength,
Low Cost
Aramid
High Strength,
Low Density
HS Carbon
UHM Carbon
High Strength
and Stiffness
Very High
Stiffness
Disadvantages
Low Stiffness,
Fatigue
Low Compr.
Str., High
Moisture
Absorption
High Cost
Low Strength,
High Cost
FIBER ORIENTATION
• ANISOTROPIC
• UNIDIRECTIONAL
• BIAS - TAILORED DIRECTION
– 0O - flexural strengthening
– 90O - column wraps
– + /- 45O - shear strengthening
• ANGLE VARIES BY APPLICATION
DEGREE OF ANISOTROPY OF
FRP COMPOSITES
FRP Composite E1/E2 E1/G12 F1/F2t
Steel
1.00
2.58
1.00
Vinyl Ester
1.00
0.94
1.00
S-Glass/Epoxy
2.44
5.06
28
E-Glass/Epoxy
4.42
8.76
17.7
Carbon/Epoxy
13.64 19.1
41.4
UHM/Epoxy
40
70
90
Kevlar/Epoxy
15.3
27.8
260
PROPERTIES OF
UNIDIRECTIONAL
COMPOSITES
Property
E-Glass/
Epoxy
Fiber Volume
0.55
Longitudinal Modulus GPa 39
Transverse .Modulus,
8.6
GPa
Shear Modulus,
3.8
GPa
Poisson’s
0.28
Ratio
Long.Tensile Strength
1080
MPa
Compressive Strength,
620
MPa
S-Glass/
Epoxy
0.50
43
8.9
Aramid/ Carbon/
Epoxy Epoxy
0.60
0.63
87
142
5.5
10.3
4.5
2.2
7.2
0.27
0.34
0.27
1280
1280
2280
690
335
1440
ELASTIC AND SHEAR MODULI
OF FRP COMPOSITES
Material
E1
E2
G12
Aluminum
10.40 10.40 3.38
Steel
29
G13
G23
3.38
3.38
29
11.24 11.24 11.24
Carbon/Epoxy 20
1.30
1.03
1.03
0.90
Glass/Epoxy
2.60
1.25
1.25
0.50
7.80
REINFORCEMENTS
SUMMARY
• TAILORING MECHANICAL PROPERTIES
– TYPE OF FIBER
– PERCENTAGE OF FIBER
– ORIENTATION OF FIBER
COMPARISON OF AXIAL AND
FLEXURAL EFFICIENCY OF FRP
SYSTEMS
Material
AXIAL
EFFICIENCY
Rank
E/
FLEXURAL
EFFICIENCY
Rank
E1/2/
Carbon/Epoxy
113.1
1
8.4
1
Kevlar/Epoxy
52.1
2
6.0
2
E-Glass/Epoxy
21.4
4
3.5
3
Mild Steel
25.6
3
1.8
4
DESIGN VARIABLES
FOR COMPOSITES
• TYPE OF FIBER
• PERCENTAGE OF FIBER or FIBER VOLUME
• ORIENTATION OF FIBER
– 0o, 90o, +45o, -45o
• TYPE OF POLYMER (RESIN)
• COST
• VOLUME OF PRODUCT - MANUFACTURING
METHOD
DESIGN VARIABLES
FOR COMPOSITES
• PHYSICAL:
– tensile strength
– compression strength
– stiffness
– weight, etc.
• ENVIRONMENTAL:
– Fire
– UV
– Corrosion Resistance
TAILORING COMPOSITE
PROPERTIES
• MAJOR FEATURE
• PLACE MATERIALS WHERE NEEDED ORIENTED STRENGTH
– LONGITUDINAL
– TRANSVERSE
– or between
• STRENGTH
• STIFFNESS
• FIRE RETARDANCY
STRUCTURAL DESIGN
APPROACH FOR COMPOSITES
Structural Design With FRP Composites
STRUCTURE
FRP Repair
Matrix, Fibers
Micromechanics
Lamina, Laminate
Macromechanics
Structural Analysis
Strengthening Design
SPECIFIC MODULUS AND STRENGTH
OF FRP COMPOSITE
FLOW CHART FOR DESIGN OF
FRP COMPOSITES
[E]1,2
Engineering Constants
[Q]1,2
Mathematical Constants
[Fiber Orientation]
[S] 1,2
Mathematical Constants
[Q] x,y
Transformed Math. Constants
[S] x,y
Transformed Math. Constants
[E] x,y
Transformed Eng. Constants
[E] x,y
Transformed Eng. Constants
MANUFACTURING
PROCESSES
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Hand Lay-up/Spray-up
Resin Transfer Molding (RTM)
Compression Molding
Injection Molding
Reinforced Reaction Injection Molding (RRIM)
Pultrusion
Filament Winding
Vacuum Assisted RTM (Va-RTM)
Centrifugal Casting
PROCESS CHARACTERISTICS
Hand Lay-up/Spray-up
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MAX SIZE:
PART GEOMETRY:
PRODUCTION VOLUME:
CYCLE TIME:
SURFACE FINISH:
TOOLING COST:
EQUIPMENT COST:
Unlimited
Simple - Complex
Low - Med
Slow
Good - Excellent
Low
Low
PRODUCT CHARACTERISTICS
Pultrusion
•
•
•
•
•
CONSTANT CROSS SECTION
CONTINUOUS LENGTH
HIGH ORIENTED STRENGTHS
COMPLEX PROFILES POSSIBLE
HYBRID REINFORCEMENTS
MATERIAL PROPERTIES
• PROPERTIES OF FRP COMPOSITES VARY
DEPENDING ON:
– TYPE OF FIBER & RESIN SELECTED
– FIBER CONTENT
– FIBER ORIENTATION
– MANUFACTURING PROCESS
REPAIR
• HYBRIDS (SUPER COMPOSITES): TRADITIONAL
MATERIALS ARE JOINED WITH FRP
COMPOSITES
– WOOD
– STEEL
– CONCRETE
– ALUMINUM
BENEFITS - SUMMARY
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LIGHT WEIGHT
HIGH STRENGTH to WEIGHT RATIO
COMPLEX PART GEOMETRY
COMPOUND SURFACE SHAPE
PARTS CONSOLIDATION
DESIGN FLEXIBILITY
LOW SPECIFIC GRAVITY
LOW THERMAL CONDUCTIVITY
HIGH DIELECTRIC STRENGTH
LIFE CYCLE ECONOMICS
• PLANNING/DESIGN/DEVELOPMENT
COST
• PURCHASE COST
• INSTALLATION COST
• MAINTENANCE COST
• LOSS/WEAR COST
• LIABILITY/INSURANCE COSTS
• DOWNTIME/LOST BUSINESS COST
• REPLACEMENT/DISPOSAL/RECYCLING
COST
LIFE CYCLE ECONOMICS
(Examples)
• IBACH BRIDGE (SWITZERLAND)
– CFRP LAMINATES- 50 TIMES MORE
EXPENSIVE THAN STEEL PER KILOGRAM
– CFRP LAMINATES- 9 TIMES MORE EXPENSIVE
THAN STEEL BY VOLUME
– REPAIR WORK REQUIREMENTS-175 KG STEEL
OR 6.2 KG CFRP
– MATERIAL COST-20 % OF THE TOTAL
PROJECT COST
LIFE CYCLE ECONOMICS
(Examples)
• HORSETAIL CREEK BRIDGE (OREGON)
– CONVENTIONAL REPAIR (SHEAR ONLY-ONE
BEAM)-$69,000
– FRP REPAIR (GFRP SHEAR ONLY-ONE BEAM)$1850
– FRP REPAIR [SHEAR (GFRP)+ FLEXURE(CFRP),
ONE BEAM]- $9850
CONCLUSIONS
• ECONOMICS ARE MORE THAN THE BASIC
ELEMENTS OF MATERIALS, LABOR,
EQUIPMENT, OVERHEAD, ETC.
• ENTIRE LIFE CYCLE ECONOMICS MUST BE
CONSIDERED AND COMPARED TO THAT OF
TRADITIONAL MATERIALS TO DETERMINE THE
BENEFITS OF COMPOSITES IN A GIVEN
APPLICATION
STRUCTURAL DESIGN WITH
FRP COMPOSITES
EXTERNAL REINFORCEMENT OF
RC BEAMS USING FRP
• BACKGROUND
• DESIGN MODELS
–
–
–
–
LACK OF DUCTILITY
FLEXURAL STRENGTHENING
SHEAR STRENGTHENING
PRESTRESSED FRP APPLICATION
• DESIGN METHODOLOGY AND
ANALYSIS
• OTHER ISSUES
– FATIGUE, CREEP, LOW TEMPERATURE FRP
PERFORMANCE
• DESIGN EXAMPLES
FRP STRENGTHENED BEAMS
BACKGROUND
• FRP VS. EXTERNALLY STEEL BONDED
PLATES
– CORROSION AT THE EPOXY-STEEL INTERFACE
– STEEL PLATES DO NOT INCREASE STRENGTH, JUST
STIFFNESS
– HIGH TEMPERATURES PERFORMANCE
DIFFICULTIES DUE TO HEAVY WEIGHT OF THE
STEEL PLATES
– STRENGTHENING DESIGN BASED ON MATERIAL
WEIGHT, NOT STRUCTURAL NEEDS
– CONSTRUCTION DIFFICULTIES
– TIME CONSUMING, HEAVY EQUIPMENT NEEDED
FRP STRENGTHENED BEAMS
LACK OF DUCTILITY
• LINEAR STRESS-STRAIN PROFILE
• DEFINITION OF DUCTILITY
– DEFLECTION AT ULTIMATE/DEFLECTION AT YIELDNOT APPLICABLE FOR FRP MATERIAL
– STRAIN-ENERGY ABSORPTION, I.E., AREA UNDER
LOAD-DEFLECTION CURVE- OK FOR FRP
COMPOSITES
– IN GENERAL- THE HIGHER THE FRP FRACTION
AREA, THE LOWER THE ENERGY ABSORPTION OF
THE STRENGTHENED CONCRETE BEAM
FRP STRENGTHENED BEAMS
TYPICAL LOAD-DEFLECTION
CURVE
FRP REINFORCED BEAMSFAILURE MODES
FRP REINFORCEMENT OF RC
COLUMNS
• Advantages of Strengthening Columns with
FRP Jackets
–
–
–
–
–
Increased Ductility
Increased Strength
Low Dead Weight
Reduced Construction Time
Low Maintenance
FRP REINFORCEMENT OF RC
COLUMNS
• Factors Influencing the Behavior of FRPRetrofitted Columns
–
–
–
–
–
Column composition
Column geometry
Current condition
Type of loading
Environmental conditions
DESIGN OF FRP RETROFIT OF
RC COLUMNS
• Shear Strengthening
• Flexural Hinge Confinement
• Lap Splice Clamping
LOAD-DISPLACEMENT CURVE
(Before Strengthening)
LOAD-DISPLACEMENT CURVE
(After Strengthening)
COLUMN DUCTILITY
FRP REINFORCEMENT OF RC
COLUMNS
• Advantages of Strengthening Columns with
FRP Jackets
–
–
–
–
–
Increased Ductility
Increased Strength
Low Dead Weight
Reduced Construction Time
Low Maintenance
FRP REINFORCEMENT OF RC
COLUMNS
• Factors Influencing the Behavior of FRPRetrofitted Columns
–
–
–
–
–
Column composition
Column geometry
Current condition
Type of loading
Environmental conditions
LOAD-DISPLACEMENT
CURVE
(Before Strengthening)
LOAD-DISPLACEMENT CURVE
(After Strengthening)
COLUMN DUCTILITY
CONSTRUCTION PROCESS
•
•
•
•
•
•
•
Preparation of the Concrete Surface
Mixing Epoxy, Putty, etc.
Preparation of the FRP Composite System
Application of the FRP Strengthening System
Anchorage (if recommended)
Curing the FRP Material
Application of Finish System
CONCRETE SURFACE
PREPARATION
• Repair of the existing concrete in accordance to:
– ACI 546R-96 “Concrete Repair Guide”
– ICRI Guideline No. 03370 “Guide for Surface
Preparation for the Repair of Deteriorated
Concrete...”
• Bond Between Concrete and FRP Materials
– Should satisfy ICRI “Guide for Selecting and
Specifying Materials for Repair of Concrete
Surfaces”
CONCRETE SURFACE
PREPARATION
• Repair Cracks 0.010 inches or Wider
– Epoxy pressure injected
– To satisfy Section 3.2 of the ACI 224.1R-93 “Causes,
Evaluation and Repair of Cracks…”
• Concrete Surface Unevenness to be Less than 1
mm
• Concrete Corners- Minimum Radius of 30 mm
APPLICATION OF THE FRP
COMPOSITE
• In Accordance to Manufacturer’s and Designer's
Specifications
–
–
–
–
–
Priming
Putty Application
Under-coating with Epoxy Resin
Application of the FRP Laminate/ FRP Fiber Sheet
Over-coating with Epoxy Resin
CURING OF THE FRP
COMPOSITES
• In Accordance to Manufacturer’s Specifications
– Temperature ranges and Curing Time- varies from
few hours to 15 days for different FRP systems
• Cured FRP Composite
– Uniform thickness and density
– Lack of porosity
CONSTRUCTION PROCESS
• Typical RC Beam in
Need for Repair
– corroded steel
– spalling concrete
CONSTRUCTION PROCESS
• Deteriorated Column /
Beam Connection
CONSTRUCTION PROCESS
• Concrete Surface
Preparation
– Smooth, free of dust and
foreign objects, oil, etc.
– Application of primer
and putty (if required by
the manufacturer)
CONSTRUCTION PROCESS
• Preparation of the FRP
Composites for
Application
– Follow
manufacturer’s
recommendations
CONSTRUCTION PROCESS
• Priming of the Concrete
Surface
• Application of the
Undercoating epoxy
Layer (adhesive when
FRP pultruded laminates
are used)
CONSTRUCTION PROCESS
• Application of CFRP
Fiber Sheet on a BeamWet Lay-Up Process
• Similar for Application of
Pultruded Laminates
CONSTRUCTION PROCESS
• Column Wrapping with
Automated FRP
Application device
CONSTRUCTION PROCESS
• Robo Wrapper by Xxsys
Technologies
CONSTRUCTION PROCESS
• Column Wrapping
Device