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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
• TRANSPORTATION• CONSTRUCTION• MARINE• CORROSION-RESISTANT• CONSUMER• ELECTRICAL/ELECTRONIC• APPLIANCES/BUSINESS• AIRCRAFT/DEFENSE
U.S. COMPOSITES SHIPMENTS - 1996 MARKET SHARESEMI-ANNUAL STATISTICAL REPORT - AUGUST 26, 1996
Includes reinforced thermoset and thermoplasticresin composites, reinforcements and
fillers.
Includes reinforced thermoset and thermoplasticresin composites, reinforcements and
fillers.SOURCE: SPI Composites InstituteSOURCE: SPI Composites Institute
Transportation 30.6%
Other- 3.4%
Aircraft/Aerospace 0.7%
Appliance/Business Equipment - 5.3%
Construction 20%
ConsumerProducts - 6%
Marine - 11.6%Electrical/Electronic - 10%
Corrosion-ResistantEquipment - 12.4%
Infrastructure Benefits• 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
CompositesResin Type
Density (kg/m3)
Tensile Str.
(MPa)
Elong. (%)
E-Mod. (GPa)
Long.Term 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 3 120-200
Phenolic 1.2 40-50 1-2 3 120-150
MATERIAL: FIBERREINFORCEMENTS
• 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 PROPERTIESDENSITY (g/cm3)
1.38
1.59
1.99
1.99
2.76
8
0 2 4 6 8 10
Aramid
Carbon
S-Glass
E-Glass
Alum
Steel
FIBER PROPERTIESTENSILE STRENGTH
x103 psi
500
525
530
625
20
60
0 200 400 600 800
E-Glass
Aramid
Carbon
S-Glass
Steel
Alum
FIBER PROPERTIESSTRAIN TO FAILURE
(%)
1.4
2.8
4.8
5
0.2
0.16
0 1 2 3 4 5 6
Carbon
Aramid
E-Glass
S-Glass
Steel
Alum
FIBER PROPERTIESTENSILE MODULUS
106 psi
10.5
12.6
19
33.5
29
10
0 10 20 30 40
E-Glass
S-Glass
Aramid
Carbon
Steel
Alum
FIBER PROPERTIESCTE - Longitudinal
x10-6/0C
-2
0.5
2.9
56.5
12.6
-2
0
2
4
6
8
10
12
14
Aramid Carbon S-Glass E-Glass Steel Alum
FIBER PROPERTIESTHERMAL CONDUCTIVITY
x10-6/0C
BTU-in/hr-ft2 - 0F
1.5115
1500
7.50
200
400
600
800
1000
1200
1400
1600
FRP Steel Alum Concrete
FIBER REINFORCEMENT
• GLASS (E-GLASS)– MOST COMMON FIBER USED– HIGH STRENGTH– GOOD WATER RESISTANCE– GOOD ELECTRIC INSULATING PROPERTIES– LOW STIFFNESS
GLASS TYPES
• 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
FiberType
Density(kg/m3)
E-Modulus
(GPa)
TensileStrength
(GPa)
Elong.(%)
E-Glass 2.54 72.5 1.72-3.45 2.5
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)
1.80 227 2.80-5.10 1.1
Carbon(HM)
1.80-1.86 370 1.80 0.5
Carbon(UHM)
1.86-2.10 350-520 1.00-1.75 0.2
ADVANTAGES AND DISADVANTAGES OF
REINFORCING FIBERSFiber Type Advantages Disadvantages
E-Glass, S-Glass High Strength,Low Cost
Low Stiffness,Fatigue
Aramid High Strength,Low Density
Low Compr.Str., HighMoistureAbsorption
HS Carbon High Strengthand Stiffness
High Cost
UHM Carbon Very HighStiffness
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
COMPOSITESProperty E-Glass/
EpoxyS-Glass/Epoxy
Aramid/Epoxy
Carbon/Epoxy
Fiber Volume 0.55 0.50 0.60 0.63Longitudinal Modulus GPa 39 43 87 142Transverse .Modulus,GPa
8.6 8.9 5.5 10.3
Shear Modulus,GPa
3.8 4.5 2.2 7.2
Poisson’sRatio
0.28 0.27 0.34 0.27
Long.Tensile StrengthMPa
1080 1280 1280 2280
Compressive Strength,MPa
620 690 335 1440
ELASTIC AND SHEAR MODULI OF FRP COMPOSITES
Material E1 E2 G12 G13 G23
Aluminum 10.40 10.40 3.38 3.38 3.38
Steel 29 29 11.24 11.24 11.24
Carbon/Epoxy 20 1.30 1.03 1.03 0.90
Glass/Epoxy 7.80 2.60 1.25 1.25 0.50
REINFORCEMENTSSUMMARY
• TAILORING MECHANICAL PROPERTIES– TYPE OF FIBER– PERCENTAGE OF FIBER– ORIENTATION OF FIBER
COMPARISON OF AXIAL AND FLEXURAL EFFICIENCY OF FRP
SYSTEMS
AXIALEFFICIENCY
FLEXURALEFFICIENCY
Material E/ Rank E1/2/ Rank
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 VARIABLESFOR 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 VARIABLESFOR 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
S tru c tu ra l D es ig n W ith F R P C om p os ites
M atrix, F ib ersM ic rom ech an ics
L am in a , L am in a teM ac rom ech an ics
S tru c tu ra l A n a lys isS tren g th en in g D es ig n
S TR U C TU R EF R P R ep a ir
SPECIFIC MODULUS AND STRENGTH OF FRP COMPOSITE
FLOW CHART FOR DESIGN OF FRP COMPOSITES
[E ] x,yTran s fo rm ed E n g . C on s tan ts
[Q ] x,yTran s fo rm ed M ath . C on s tan ts
[Q ]1 ,2M ath em atica l C on s tan ts
[F ib er O rien ta tion ]
[E ] x,yTran s fo rm ed E n g . C on s tan ts
[S ] x,yTran s fo rm ed M ath . C on s tan ts
[S ] 1 ,2M ath em atica l C on s tan ts
[E ]1 ,2E n g in eerin g C on s tan ts
MANUFACTURING PROCESSES
• 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 CHARACTERISTICSHand Lay-up/Spray-up
• MAX SIZE: Unlimited• PART GEOMETRY: Simple - Complex• PRODUCTION VOLUME: Low - Med• CYCLE TIME: Slow• SURFACE FINISH: Good - Excellent• TOOLING COST: Low• EQUIPMENT COST: Low
PRODUCT CHARACTERISTICSPultrusion
• 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
• 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 BEAMSBACKGROUND
• 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 BEAMSLACK OF DUCTILITY
• LINEAR STRESS-STRAIN PROFILE• DEFINITION OF DUCTILITY
– DEFLECTION AT ULTIMATE/DEFLECTION AT YIELD- NOT 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 BEAMS- FAILURE 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 FRP-Retrofitted 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 FRP-Retrofitted 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 Beam- Wet 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