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Bridge Product Gateway

External Reinforcement Systems Concrete Repair,

Strengthening, and Seismic Retrofit

Introduction

FRP products were first used to reinforce concrete structures in the 1950s.

During the next two decades, the quality of the FRP materials improved

considerably, manufacturing methods became more automated and

material costs decreased. The use of these materials for external

reinforcement of concrete bridge structures started in the 1980s, first as a

substitute to steel plate bonding and then as a substitute for steel

confinement shells for bridge columns.

The technology for external retrofitting was developed primarily in Japan

(sheet wrapping) and Europe (laminate bonding). Today there are more

than 1000 concrete slab/steel girder bridges in Japan that have been

strengthened with sheet bonding to the slabs. Also, many thousands of

bridge columns have been seismically upgraded with the same materials.

Ongoing development of cost-effective production techniques for FRP

composites has progressed to the level that they are ready for the

construction industry. Reduced material cost, coupled with labor savings

inherent with its low weight and comparably simpler installation, relatively

unlimited material length availability, and immunity to corrosion, make

FRP materials an attractive solution for post strengthening, repair, seismic

retrofit, and infrastructure security.

The principles behind externally bonding FRP plates or wraps to concrete

structures are very similar to the principles used in application of bonded

steel plates. In general, the members flexural, shear, or axial strength is

increased or better mobilized by the external application of high tensile

strength material.

Reasons for applying FRP systems as an external reinforcement for bridge

structures:

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Capacity upgrade due to a change in use of a structure

Passive confinement to improve seismic resistance

Crack control

Strengthening around new openings in slabs

FRP composite systems have been applied to many structural elements

including beams, columns, slabs and walls as well as many special

applications such as chimneys, pipes and tanks. More recently this

technology has been applied to infrastructure security applications relating

to hardening and blast mitigation of structures.

Add Shear and Flexural Capacity

in Reinforced Concrete Beams for

strengthening and seismic

upgrade.

Add Confinement and flexure to

Reinforced Concrete Columns for

seismic upgrade and

strengthening

Add Flexural Capacity toReinforced Concrete Slabs in the

Positive & Negative Moment

Areas.

In lightly reinforced and

unreinforced masonry (URM),

such as concrete masonry units

and brick, FRP material systems

have demonstrated multiple

benefits by adding shear and

flexural capacity, ductility for

seismic upgrade, and in some

cases, blast resistance for the

hardening of buildings for

industrial applications.


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FRP composite systems can be categorized based on how they are

delivered to the site and installed. External FRP composites systems come

in a variety of forms under the general categories of 1) wet lay-up

systems, and 2) precured systems. The FRP composite system and its form

should be selected based on the acceptable transfer of structural loads,

load capacity, and ease and simplicity of installation.

Features and Benefits

Repair

FRP composite systems can be used to repair damaged concrete structures.

The FRP is used in combination with resin crack injection, cementitous

repair mortars, epoxy grouts, etc., to repair the section and restore it to

pre-damaged load ratings. Repair of concrete structures caused by

corroding steel rebar can be accomplished provided the corroded elements

are repaired or replaced and the source of corrosion is addressed. The

repair of any element in a structure must be approached as project-

specific. The type of composite, the number of layers, the orientation of

fibers, and the preliminary work and surface preparation all depend on the

design goals and type of structural element as determined by the project.

Strengthening

FRP composite systems can be used to strengthen undamaged concrete

structures that require greater load capacity due to functional changes,

additional loads, code changes or other reasons. The FRP is placed on

tensile surfaces in a manner similar to steel plate bonding for

strengthening or embedded into saw cut grooves near the concrete

surface. FRP composite systems can add shear and flexural strength to

beams and slabs for both positive and negative moment conditions.

Strengthening of existing concrete structural members with FRP

composites is accomplished by utilizing the tensile strength and stiffness of

the composite and the strain compatibility of the composite to the existing

member. The design must include proper selection of the adhesive used to

bond the FRP reinforcement to the surface of the concrete to be

strengthened. As in repair, the type of composite, the number of layers,

the orientation of fibers, and the preliminary work and surface preparation

all depend on the design goals and type of structural element as

determined by the project.

Seismic Retrofit

FRP composite systems have been used extensively in seismic zones for

confinement of concrete columns and walls. A number of FRP systems

have been qualified for use by State DOTs for wrapping circular and


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rectangular bridge columns. Improvements in ductility factors of up to 10

fold have been realized through the use of FRP column wrapping. Specific

FRP systems, offered by some of the manufacturers referenced below,

address seismic requirements according to the load capacities anticipated

and geometric considerations of the building structure. In addition, FRP

systems can be used for stabilizing hollow clay tile, brick and other

unreinforced and lightly reinforced masonry walls in life-safety applications

where vital egress and exit paths in buildings are required.

Codes and Specifications

The designer or end-user considering the use of FRP composite systems for

the repair, strengthening or seismic upgrade of existing structures should

reference:

USA

ACI 440.2R-02, Guide for the Design and Construction of

Externally Bonded FRP Systems for Strengthening Concrete

Structures, American Concrete Institute, 2002.

Europe

Europe fib Bulletin 14, Externally Bonded FRP Reinforcement for

RC Structures, Federation Internationale du Beton, 2001, ISSN1562-3610.

Canada

CSA S806-02, Design and Construction of Building Components

with Fiber-Reinforced Polymers, Canadian Standards Association,

May 2002, ISBN 1-55324-853-8.

Design Guide Manuals

Strengthening Reinforced Concrete Structures with Externally

Bonded Fibre-Reinforced Polymers, ISIS Canada,

www.isiscanada.com

FRP Systems

FRP system forms can be categorized based on how they are delivered to

the site and installed. External FRP reinforcing systems come in a variety offorms including 1) wet layup systems, 2) precured systems and 3) Near

Surface Mounted Systems (NSM).


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Overview of Wet Lay-up Systems

Wet lay-up FRP systems consist of dry unidirectional or multidirectional

fiber sheets or fabrics that are impregnated on-site with a saturating resin.

The saturating resin is used to provide a binding matrix for the fiber and

bond the sheets to the concrete surface. Wet lay-up systems are saturated

with resin and cured in place and in this sense are analogous to

cast-in-place concrete. Three common types of wet lay-up systems are

listed below:

Products

Dry unidirectional fiber sheets with the fiber running predominantly

in one planar (0 axis) direction

Dry multidirectional fiber sheets or fabrics with fibers oriented in at

least two planar directions

Dry fiber tows that are wound or otherwise mechanically applied to

the concrete surface. The dry fiber tows are impregnated with resin

during the winding operation.

Installation/Application

Prepare Substrate The concrete, masonry or steel surface must

be properly prepared prior to bonding. There shall be no spalling or

delamination in the case of concrete and the corners must be ground

to a minimum radius of 10mm (3/8 in.). The bearing substrate

surface is typical roughened by grinding or sandblasting.

Sandblasting is normally used on steel. Any unevenness in the

concrete or masonry is removed with a mineral-based re-profiling

mortar.

1.

Prime Concrete Surface Some systems require that the

dust-free surface be coated with a primer. For steel a sandblasted

surface yields the best results.

2.

Apply Epoxy To saturate the sheet and simplify installation, the

adhesive/matrix resin is applied to the front and back of the

material. Mix and apply epoxy onto surface using a roller or brush.

Once the material has been wet-out with the liquid resin, the

material may be rolled for ease of transport and/or application to the

place of application.

3.

Place FRP Sheet on Structure Unroll sheet rolls onto the4.


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structural element being strengthened. Tension is maintained to

minimize intrusion of air entrainment behind sheet. Placing one

layer at a time, apply pressure to wrap using a roller. A hard rubber

roller with ridges (air relief roller) works well for this application.

Apply Epoxy to Sheet Surface A topcoat of epoxy can now be

applied to the sheet to fully saturate the material. If applicable,

quartz sand can be applied to topcoat prior to curing to provide a

textured surface for plaster or painting.

5.

Overview of Precured Systems

Pre-cured FRP systems consist of a wide variety of composite shapes

manufactured in the system suppliers facility and shipped to the job site.

Typically, an adhesive is used to bond the precured flat sheets, rods or

shapes to the concrete surface or inserted into slots cut into the wall. The

adhesive used to bond the precured system to the concrete surface must

be specified by the system manufacturer. Adhesive selection is critical in

that the adhesive provides for the proper transfer of load between the

surface of the concrete and the cured reinforcement. Common types of

pre-cured systems are listed below:

Products

Precured unidirectional laminate sheets in the form of large flat plate

stock or as thin ribbon strips coiled on a roll.

Precured multidirectional grids coiled on a roll or precut in sheet

form. Grids are able to be cut easily in the field using tin-snips.

Precured shells in the form of shell segments cut so they can be

opened and fitted around columns or other elements. Multiple shell

layers are bonded to the concrete and to each other to provide

seismic confinement or strengthening.

Precured Grids

Grids are generally produced with glass fiber or carbon fiber and are

wet-out with a resin and fully cured in the manufacturers factory. Grids

are produced in a variety of constructions from unidirectional to a

balanced construction. Grid reinforcements can be supplied with a wide

range of tensile strength properties. Tensile strengths in both the warp

and weft direction can be varied. Typically grid thickness ranges from

0.01 0.100 and grid-opening sizes from 0.125 to 2 in. The product is

typically supplied in rolls although it may be cut to length and supplied in


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sheet form. The product can be cut to size with a heavy-duty scissors or

tin snips. The grids are produced so the degree of cure and alignment is

controlled. The equipment used to produce these structural grids insures

that warp and weft continuous fibers are uniformly tensioned for

consistent and uniform fiber loading.


Typically an adhesive is used to bond the precured flat sheets, rods or

shapes to the concrete surface or inserted into slots cut into the substrate.

The system manufacturer must specify the adhesive used to bond the

precured system to the concrete surface. Adhesive selection is critical for

the proper transfer of load between the surface of the concrete and the

precured reinforcement. If an adhesive is not used, the system

manufacturer will provide details on the method for affixing their

reinforcement system to the surface of the concrete. Applying precured

systems is similar to wet lay-up system. The procedures are as follow:

Prepare Substrate The concrete, masonry or steel surface must

be properly prepared prior to bonding. There shall be no spalling or

delamination in the case of concrete and the corners must be ground

to a minimum radius of 10mm (3/8 in.) or the recommendations of

the precured system manufacturer. The substrate surface is typically

roughened by grinding or sandblasting. Sandblasting is normallyused on steel. Any unevenness in the concrete or masonry is

removed with a mineral-based re-profiling mortar. Trowelable

adhesives fill small holes or uneven surfaces before applying FRP

systems.

1.

Prime Concrete Surface Some systems require the dust-free

surface be coated with a primer. Follow the system manufacturers

recommended procedure. For steel, a sandblasted surface yields the

best results.

2.

Apply Epoxy The majority of systems require an adhesive be

applied to the surface of the concrete, masonry or steel prior to the

FRP precured reinforcement being pressed into the surface of the

adhesive. If this is not the case, follow the system manufacturers

recommended procedures. The adhesive thickness is critical to the

performance of the system. Follow the system manufacturers

recommendation regarding the thickness of the adhesive to

be applied. The adhesive is applied to the surface using a steel or

plastic trowel or squeegee. Each adhesive has a working time at a

specific temperature. This information is available from the system

3.


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manufacturer.

Place FRP Precured material on the Structure After the

adhesive has been applied to the surface of the concrete, masonry or

steel, the precured FRP material should be placed in contact with the

adhesive and pressed into the surface of the adhesive following

recommendations from the system manufacturer.

4.

Cosmetic Topcoat A topcoat of epoxy can now be applied to the

sheet to provide a cosmetic finish. If applicable, quartz sand can be

applied to the topcoat to provide a textured surface for plaster or

painting.

5.

Note: Installation/Application of procured grids follow the method

described above. The surface of the structure to be strengthened will have

a trowelable epoxy adhesive applied to the surface after the surface has

been prepared. The grids are then pressed into the surface of the epoxy

adhesive with the excess adhesive coming through the holes in the grids

as the grid is wrapped around the column or onto other surfaces to give

the correct number of layers to meet the design requirements. Following

the completion of the application of the grids, the excess epoxy adhesive

on the surface is smoothed to encapsulate the exterior of the grid

structure to create the finished structural grid system to create the

strengthening system.

Precured Shapes for Near Surface Mounted (NSM) Application

Pre-cured NSM rod/shape systems can generally be used as an alternative

for reinforcing concrete and masonry structures similar to surface

laminates. NSM Rods/shapes provide a more discrete solution to

strengthening structures in that they generally are inserted into the

masonry or concrete structure via slot or saw cuts. Generally, shapes can

vary in size depending on application but typically are provided in roundand rectangular cross-sections. The shapes are manufactured in the

system suppliers facility and shipped to the job site. The shapes generally

feature a surface treatment to facilitate bond between the FRP and

adhesive or grout. An epoxy adhesive or cementitious grout is used to

bond the precured rods in the groove cut into the surface Adhesive

selection is critical in that the adhesive provides for the proper transfer of

load between the wall and the cured reinforcement. A cosmetic surface

can then be added to completely hide the strengthening system. Since the

products are embedded into the substrate and bonded on three sides of

the FRP shape, development lengths for NSM strengthening may be

shorter. NSM rods/shapes may also be anchored into adjacent members


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and the opportunity of upgrading elements in their negative moment

region is opened-up, as the FRP shape is not exposed to potential

mechanical damage typical of floor or deck systems. FRP rods/shapes

using the NSM technique does not require extensive surface preparation

and installation time may be less than other systems. The American

Concrete Institute Committee 440 is presently reviewing modifications to

ACI440.2R-02 to document design methodologies for FRP/NSM

strengthening.


After assessment of the condition of the existing structure and design by a

competent professional, installation of the NSM FRP strengthening is

performed according to the following general guide:

Cut Groove Using a diamond blade saw or grinder, a groove 1.5

times the bar diameter (in the case of a rectangular FRP shape, 1.5

times the depth and 3 times the thickness) is cut as prescribed. The

use of two diamond blades on the saw arbor may be necessary.

1.

Prepare Groove The groove is masked with masking tape or

similar product to prevent excess adhesive from marring the surface.

The groove is thoroughly cleaned using a vacuum and/or compressed

air.

2.

Apply Adhesive Structural adhesive gel or grout is filled in the

groove. Care should be taken to avoid entrapped air voids.

3.

Place FRP rod/shape Into Groove After the adhesive has been

applied into the groove, the rod is placed and pressed into the

groove to insure proper location of the rod/shape.

4.

Finish After the FRP rod/shape is seated into the groove, the

adhesive is smoothed and any additional adhesive is added. General

clean up and removal of the masking.

5.

Concrete Repair Suppliers

Edge Structural Composites, Inc.

145 Park Place

Richmond, CA 94804

www.edgefrp.comCONTACT: Karl Gillette

P: 510-233-8654

F: 510-233-8673

E: [email protected]

Gordon Composites, Inc.

2350 Air Park Way

Montrose CO 81401

www.gordoncomposites.com

CONTACT: Ed Pilpel (Technical)

P: 800-575-5771

F: 970-240-2853


CONTACT: Todd Hobbs


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(Sales)

P: 800-399-0757

F: 970-240-2853


Hexcel Schwebel Civil

Engineering and Construction

Systems, Inc.

2200 South Murray Avenue

Anderson, SC 29622

www.hexcel.com

CONTACT: Fred Isley

P: 864-260-6593

F: 864-260-6581


Hughes Brothers, Inc.

210 N. 13th Street

Seward, NE 68434

www.hughesbros.com

CONTACT: Doug Gremel

(Technical)

P: 800-869-0359

F: 402-643-2149

[email protected]

Saint-Gobain Technical Fabrics

345 Third Street, Suite 615

Niagara Falls, NY 14303

www.sgtf.com

CONTACT: Thom Palmer

P: 716-285-0731

F: 716-285-1078


Sika Corporation

201 Polito Avenue

Lyndhurst, NJ 07071

www.sikausa.com

CONTACT: David White, P.E.

P: 201-933-8800

F: 201-933-6225


TechFab, LLC

2200 South Murray Avenue

Anderson, SC 29624

www.techfabllc.com

CONTACT: Gordon Brown

P: 864-260-3268

F: [email protected]

American Composites Manufacturers Association 1010 North Glebe Road, Arlington, VA 22201P: 703-525-0511 F: 703-525-0743 E: [email protected]

New York Office 600 Mamaroneck Avenue, Suite 429 Harrison, NY 10528P: 914-381-3572 F: 914-381-1253


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