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