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 SHARE

SEMI-ANNUAL STATISTICAL REPORT - AUGUST 26, 1996 Transportation 30.6% Aircraft/Aerospace 0.7% Construction 20% Other- 3.4% Consumer Products - 6% Electrical/ Electronic - 10% Marine - 11.6% Corrosion-Resistant Equipment - 12.4% Appliance/Business Equipment - 5.3% Includes reinforced thermoset and thermoplastic resin composites, reinforcements and fillers .

SOURCE: SPI Composites Institute

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 Composites

Resin Type Polyester Density (kg/m 3 ) 1.2 Tensile Str. (MPa) 50-65 Elong. (%) 2-3 E Mod. (GPa) 3 Long.

Term t ,(C) 120 Vinyl Ester Epoxy 1.15 70-80 1.1-1.4 50-90 4-6 2-8 Phenolic 1.2 40-50 1-2 3.5 140 3 3 120 200 120 150

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

Steel Alum E-Glass S-Glass Carbon Aramid FIBER PROPERTIES DENSITY (g/cm 3 ) 8 1.99

1.99

1.59

1.38

2.76

2 4 0 6 8 10

FIBER PROPERTIES TENSILE STRENGTH Alum Steel S-Glass Carbon Aramid E-Glass 20 60 0 200 400 530 525 500 600 625 800 x10 3 psi

FIBER PROPERTIES STRAIN TO FAILURE Alum Steel S-Glass E-Glass Aramid Carbon 0.2

0.16

0 1 1.4

2 2.8

3 4 5 4.8

5 6 (%)

Alum Steel Carbon Aramid S-Glass E-Glass FIBER PROPERTIES TENSILE MODULUS 10 19 10 12.6

10.5

20 29 33.5

0 30 40 10 6 psi

FIBER PROPERTIES CTE - Longitudinal x10 -6 / 0 C 14 12 10 8 6 4 2 0 -2 0.5

2.9

5 Aramid -2 Carbon S-Glass E-Glass 6.5

Steel 12.6

Alum

1600 1400 1200 x10 -6 / 0 C 1000 800 600 400 200 0 FIBER PROPERTIES THERMAL CONDUCTIVITY 1500 1.5

FRP 115 Steel BTU-in/hr-ft 2 0 F Alum 7.5

Concrete

FIBER REINFORCEMENT

• GLASS (E-GLASS) – MOST COMMON FIBER USED – HIGH STRENGTH – GOOD WATER RESISTANCE – GOOD ELECTRIC INSULATING PROPERTIES – LOW STIFFNESS

• E-GLASS • S-GLASS • C-GLASS • ECR-GLASS • AR-GLASS

GLASS TYPES

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/m 3 ) E-Glass S-Glass Kevlar 29 Kevlar 49 Carbon (HS) Carbon (HM) Carbon (UHM) 2.54

2.49

1.45

1.45

1.80

1.80-1.86

1.86-2.10

E Modulus (GPa) 72.5

87 85 117 227 370 350-520 Tensile Strength (GPa) 1.72-3.45

2.53-4.48

2.27-3.80

2.27-3.80

2.80-5.10

1.80

1.00-1.75

Elong.

(%) 2.5

2.9

2.8

1.8

1.1

0.5

0.2

ADVANTAGES AND DISADVANTAGES OF REINFORCING FIBERS Fiber Type Advantages Disadvantages E-Glass, S-Glass High Strength, Low Cost Aramid High Strength, Low Density HS Carbon UHM Carbon High Strength and Stiffness Very High Stiffness Low Stiffness, Fatigue Low Compr.

Str., High Moisture Absorption High Cost Low Strength, High Cost

FIBER ORIENTATION

• ANISOTROPIC • UNIDIRECTIONAL • BIAS - TAILORED DIRECTION – 0 O - flexural strengthening – 90 O - column wraps – + /- 45 O - shear strengthening • ANGLE VARIES BY APPLICATION

DEGREE OF ANISOTROPY OF FRP COMPOSITES FRP Composite E 1 /E 2 E 1 /G 12 F 1 /F 2t

Steel 1.00 2.58 1.00 Vinyl Ester S-Glass/Epoxy 1.00 2.44 0.94 5.06 1.00 28 E-Glass/Epoxy Carbon/Epoxy UHM/Epoxy Kevlar/Epoxy 4.42 13.64 19.1 40 15.3 8.76 70 27.8 17.7 41.4 90 260

PROPERTIES OF UNIDIRECTIONAL COMPOSITES Property Fiber Volume E-Glass/ Epoxy 0.55

Longitudinal Modulus GPa 39 Transverse .Modulus, GPa Shear Modulus, GPa Poisson’s Ratio Long.Tensile Strength MPa Compressive Strength, MPa 8.6

3.8

0.28

1080 620 S-Glass/ Epoxy 0.50

43 8.9

4.5

0.27

1280 690 Aramid/ Epoxy 0.60

87 5.5

Carbon/ Epoxy 0.63

142 10.3

2.2

0.34

1280 335 7.2

0.27

2280 1440

ELASTIC AND SHEAR MODULI OF FRP COMPOSITES Material E 1 E 2 G 12 G 13 G 23

Aluminum 10.40 10.40 3.38

3.38

3.38

Steel Carbon/Epoxy 20 Glass/Epoxy 29 7.80

29 1.30

2.60

11.24 11.24 11.24

1.03

1.25

1.03

0.90

1.25

0.50

REINFORCEMENTS SUMMARY

• TAILORING MECHANICAL PROPERTIES – TYPE OF FIBER – PERCENTAGE OF FIBER – ORIENTATION OF FIBER

COMPARISON OF AXIAL AND FLEXURAL EFFICIENCY OF FRP SYSTEMS Material Carbon/Epoxy Kevlar/Epoxy E-Glass/Epoxy Mild Steel AXIAL EFFICIENCY E/



Rank

113.1

1 52.1

21.4

25.6

2 4 3

FLEXURAL EFFICIENCY E 1/2 /



Rank

8.4

1 6.0

3.5

1.8

2 3 4

DESIGN VARIABLES FOR COMPOSITES

• TYPE OF FIBER • PERCENTAGE OF FIBER or FIBER VOLUME • ORIENTATION OF FIBER – 0 o , 90 o , +45 o , -45 o • 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

[Q]1,2 Mathematical Constants [Q] x,y Transformed Math. Constants [E] x,y Transformed Eng. Constants [E]1,2 Engineering Constants [Fiber Orientation] [S] 1,2 Mathematical Constants [S] x,y Transformed Math. Constants [E] x,y Transformed Eng. Constants

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 CHARACTERISTICS Hand Lay-up/Spray-up

• MAX SIZE: • PART GEOMETRY: Unlimited Simple - Complex • PRODUCTION VOLUME: Low - Med • CYCLE TIME: Slow • SURFACE FINISH: • TOOLING COST: Good - Excellent Low • EQUIPMENT COST: 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

• 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 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