Fiber Reinforced Polymer (FRP) for the Repair & Retrofit of Existing Structures & for New Construction

THE COOPER UNION
ALBERT NERKEN SCHOOL OF ENGINEERING

Fiber Reinforced Polymer (FRP) for the
Repair & Retrofit of Existing Structures
& for New Construction

A thesis submitted in partial fulfillment
of the requirements for the degree of
Master of Engineering

Jessica Galbo, E.I.T.
May 8,2012
Professor Jameel Ahmad, Ph.D.
Chairman of Civil Engineering at Cooper Union


UMI Number: 1520342

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FRP for The Repair & Retrofit of Existing Structures & for New Construction

THE COOPER UNION FOR THE ADVANCEMENT OF SCIENCE AND ART
ALBERT NERKEN SCHOOL OF ENGINEERING

This thesis was prepared under the direction of the Candidate's Thesis Advisor and has
received approval. It was submitted to the Dean of the School of Engineering and the
full Faculty, and was approved as partial fulfillment of the requirements for the degree
of Master of Engineering.

Dean, School of Engineering - Date

rofessor Jameel Ahmad, Ph.D.

Date

Chairman of Civil Engineering at Cooper Union
Candidate's Thesis Advisor

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FRPfor The Repair & Retrofit of Existing Structures & for New Construction

Abstract
Fiber reinforced plastic and fiber reinforced polymer (FRP) materials are becoming more
widely used and accepted in the repair and retrofit of existing structures, and have limited
applications for new construction. This thesis identifies FRP's characteristics, including its properties
and behavior, its current applications, how to design with FRP, and research being done for FRP's
further development.
FRP itself is a composite material made of fibers and resins which was first developed in the
1930s. The fibers provide structural strength, and the resins help to distribute forces within the FRP
and protect the system from moisture and corrosion.
FRP can be used for retrofit, rehabilitation, and repair of existing structures, or in new
construction. Structures are most often retrofit with FRP using externally bonded FRP laminates to
provide flexural strength, shear strength, or confinement for service loading and seismic loading.
FRP can also be applied externally to prevent areas prone to corrosion or environmental damage
because it is air tight, waterproof, and corrosion-resistant. FRP can be used as a composite with
concrete internally in the form of FRP reinforcing bars for new construction. These sections will not
corrode or spall due to the noncorrosive properties of FRP compared to conventional reinforcing
steel. FRP can also be molded or pultruded into sections used as composites with concrete, or
sections made exclusively of FRP. These sections have never been used for large scale projects, and
typically have been constructed for research purposes by various state departments of
transportation.
Case studies of several types of FRP applications are presented and investigated in this
thesis to determine its anticipated benefits and limitations, and conclusions and recommendations
are presented, regarding the use of FRP materials.

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FRP for The Repair & Retrofit of Existing Structures & for New Construction

Table of Contents
Abstract

3

1.0 Introduction

7

1.1 Statement of Problem

7

1.2 Purpose of Thesis

9

2.0 FRP Applications, Composition, and Properties

10

2.1 History

10

2.2 Composition and Properties

11

2.2.1 Fibers

11

2.2.2 Resins

14

3.0 FRP for Retrofit, Rehabilitation, & Repair of Existing Structures
3.1 FRP for Tensile Reinforcement

16
16

3.1.1 Concept

16

3.1.2 Design Guidelines

18

3.1.3 Construction and Application Methods

19

3.1.4 FRP for Flexure Case Studies

20

3.2 FRP Wrapping for Shear Reinforcement

23

3.2.1 Concept

23

3.2.2 Design Guidelines

24

3.2.3 Construction

27

3.2.4 FRP for Shear Case Studies

28

3.3 FRP Wrapping for Confinement Reinforcing

30

3.3.1 Concept

30

3.3.2 Design Guidelines

35

3.3.3 Construction

37

3.3.4 Case Studies

37

3.4 FRP for Corrosion Mitigation

39

3.4.1 Concept

40

3.4.2 Design Guidelines

41

3.4.3 Construction

41

3.4.4 Case Studies

42

4.1 FRP Rebar

44
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4.1.1 Concept

44

4.1.2 Design Guidelines

47

4.1.3 Construction

48

4.1.4 FRP Rebar Case Studies

48

4.2 FRP Sections

51

4.2.1 Concept

51

4.2.2 Design Guidelines

51

4.2.3 Construction

52

4.2.4 Case Studies

54

5.0 Advantages and Disadvantages

60

6.0 Conclusions and Recommendations

63

Bibliography

64

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FRP for The Repair & Retrofit of Existing Structures & for New Construction

List of Tables
Table 1: Material Properties of Glass Fibers (Federal Highway Administration)

12

Table 2: Material Properties of Amarid Fibers (Federal Highway Administration)

12

Table 3: Material Properties of Carbon Fibers (Federal Highway Administration)

13

List of Figures
Figure 1: Stress-Strain Diagrams for Fibers (Federal Highway Administration)

13

Figure 2: Industrial Plant with FRP Strips for Flexural Strength

21

Figure 3: Photos of Peaks and Valleys of Roofing with FRP Strips

21

Figure 4: FRP Plate Strengthening of Church Street Bridge Pier Cap

22

Figure 5: Photos of Typical Rebar Arrangements in Columns (Left) and Beams (Right)

23

Figure 6: KY3297 Bridge - FRP Strips for Shear Strengthening

28

Figure 7: Challenger Middle School Footbridge: FRP U Wrap for Shear Strengthening

29

Figure 8: Mander et al. - Relationship Between Confining Stresses & Axial Strength

35

Figure 9: McKinley Tower: Conventional Repair vs. Equivalent FRP Wrapping Repair

38

Figure 10: Parking Garage Column FRP Wrapping for Axial Strength Increase

38

Figure 11:1-40 Bridge FRP Wrap for Corrosion Protection

43

Figure 12: FRP Rebar Arrangement - Longitudinal and Shear Rebar

44

Figure 13: Moment Capacity of Beam considering Rebar Development Lengths (23)

46

Figure 14: 53rd Avenue Bridge FRP Deck Reinforcing Bars

49

Figure 15: Miles Road Bridge Glass FRP Reinforcing Bar

49

Figure 16: FRP Rebar Layout and Load Test Results

50

Figure 17: FRP Beam Pultrusion Process

53

Figure 18: Construction of Concrete Filled FRP Tubes and FRP decking Neil Bridge

54

Figure 19: Composition of a Hybrid Composite Beam

55

Figure 20: Photo of Hybrid Composite Beam

56

Figure 21: Mile High Road Bridge constructed with Hybrid Composite Beam Superstructure

56

Figure 22: U Shape FRP and Concrete Beams Installed in Refugio TX byTxDOT

57

Figure 23: FRP Bridge Construction at Fort Bragg

58

Figure 24: Load Testing of FRP Bridge at Fort Bragg with Ml AbramsTank

58

Figure 25: FRP Bridge Substructure Installed at Fort Eustis

59

Figure 26: Fort Eustis Completed FRP Rail Bridge

59

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FRP for The Repair & Retrofit of Existing Structures & for New Construction

1.0 Introduction
1.1 Statement of Problem
The average age of bridges in the United States is 43 years, many of which were built
anticipating a design life of 50 years whom are approaching the end of their design lives. When the
1-35 Bridge in Minneapolis collapsed in 2007, it caused alarm for all aging infrastructure and created
an awareness of the deteriorated condition of infrastructure in the US. Regular inspections must be
made to assess the conditions of bridges, and maintenance must be performed when structural
integrity may become compromised. The conditions of bridges in the United States, as of 2009, were
given a Report Card rating of "C" by the American Society of Civil Engineers (ASCE); 26% of bridges
are considered structurally deficient or functionally obsolete. The ASCE has called for a balance
between immediate repairs, preventative measures, repair/retrofit of deficient bridges, and
replacement when necessary to keep bridges in a good state, and to maximize their lifespans. When
proper measures are taken to construct infrastructure with long lifespans, and proper maintenance
occurs over the bridge's lifespan the overall cost, called a "lifecycle cost" will be minimized. This
means that sometimes the upfront investment cost is higher during construction, but over the
structure's life it will perform better and have a significantly extended life, requiring fewer
replacements and large retrofit measures, and have lower total costs (5)*. Repair, rehabilitation,
and construction must be done in cost effective ways, which will become even more demanding as
much of the country's infrastructure reaches the end of their intended design lives. This calls for the
full utilization of advances in technology, and new materials, such as Fiber Reinforced Polymers
(FRP).
One strategy to optimize the use of available funding to maintain infrastructure is to only
spend money when it's absolutely necessary. Find and use the lowest cost designs and materials to

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* Numbers in parenthesis refer to the Bibliography.

FRP for The Repair & Retrofit of Existing Structures & for New Construction

minimize upfront investments, and to only perform repairs when absolutely necessary. But this
strategy is not proactive or preventative; it is retroactive, and typically results in high lifecycle costs.
Another strategy to construct and maintain infrastructure is to make consistent
investments, whenever necessary. This means choosing a high upfront cost option for construction
when it is anticipated the benefits will make the structure more durable, and the invested money
will be regained due to lower maintenance costs, and a longer lifespan. Consistent maintenance is to
be performed to find and eliminate problems before they advance to a state that is not easily
repaired which can compromise the structure and significantly decrease its intended lifespan.
Measures should be taken to increase the lifespan of infrastructure in order to:
•

maintain the safety and functionality of our current infrastructure,

•

reduce life-cycle construction costs,

•

protect the environment from harmful construction byproducts including the
release of carbon dioxide into the atmosphere from cement mixing, and to preserve
raw materials.

One method by which infrastructure's lifespans can be increased is through the utilization of
FRP materials. FRP can increase the lifespans of existing concrete and steel infrastructure by
providing structural upgrade where necessary and providing protection from sources of

deterioration.
FRP materials are versatile, as they can be used to repair existing infrastructure experiencing
problems with deterioration, rehabilitate overstressed structures, and for new construction. FRP is
extremely durable due to its material properties, not susceptible to corrosion, and longer lasting
with little required maintenance if installed correctly. FRP is lightweight, making it ideal for
rehabilitation projects on existing structures, for which any additional loads can cause overstresses;
therefore FRP can contribute significant strength without increasing structural loads and demands

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on the structure. Because of FRP's durability, it is ideal for use in new construction, whose lifespan
will require fewer large maintenance and repair projects due to reduced susceptibility to severe
deterioration.
Despite knowledge amongst engineers of FRP's existence and potential benefits, it is not
commonly used, and has not earned acceptance by many agencies or contractors for regular use in
construction. This thesis is intended to provide insight to the engineer on not just the benefits of
FRP, but how it works, how to design with it, and examples of its use in earlier projects. With this
knowledge, engineers can be more informed of the appropriateness of FRP for use in projects and
can make recommendations to clients and contractors in situations where FRP would be beneficial
to a project.

1.2 Purpose of Thesis
Fiber reinforced plastic and fiber reinforced polymer (FRP) materials are becoming more
widely used and accepted in the repair and retrofit of existing structures, and have limited
applications for new construction. This thesis identifies FRP's characteristics, including its properties
and behavior, its current applications, how to design with FRP, and research being done for FRP's
further development. Case studies of its uses will be presented and investigated to determine its

anticipated benefits and limitations, from which conclusions will be drawn and recommendations
presented.

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FRPfor The Repair & Retrofit of Existing Structures & for New Construction

2.0 FRP Applications, Composition, and Properties
2.1 History
Fiber reinforced polymers first emerged in the 1930s. The first fibers were made of
fiberglass, for which a mass production technique was first developed by Owens Glass Company in
1932. The first resin developed appropriate for mixing with fiberglass for strength was a polyester
resin developed by DuPont in 1936. Combining fiberglass with polyester resins produced a
composite material which could replace conventional materials which were in short supply during
the World War II era. These materials were used in US aircrafts and naval vessels, and were used for
building boats in the 1940s. By the 1950s FRP materials were being used for the fabrication of
automobiles. Fiber reinforced polymers made the mass production of boats possible, and the
boating industry's demand for the product spurred its further development and research.
The growing popularity of FRP products led to better product development, including new
vinyl and epoxy resins, and new fibers made of materials such as amarid and carbon with different
strength properties. Improvements were made in glass refinement techniques, and strand quality
increased. Fibers were also being produced in continuous mats with both uni-directional and multi­
directional fiber weaves. Epoxy resins offer superior quality, and better corrosion and weathering
resistance. Epoxy resins were expensive, so they were not first used for the boating industry, but
rather in the aerospace industry. Carbon fibers were first developed in the UK Royal Aircraft
Establishment, in 1963. Eventually FRP materials were used by the boating, aircraft, and automobile
industries, because it allowed for lightweight, corrosion resistant products. Early products
constructed of FRP materials were considerably over designed, due to uncertainties with the
material's strength. Now FRP composites are used to make all types of boats, aircrafts, automobiles,

and consumer products such as tennis rackets, fishing rods, ladders, and bathtubs.

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FRP was first used in infrastructure in the early 1980s in Europe and Asia, and was later used in the
United States in the 1990s. FRP was considered for use due to observed problems with conventional
reinforcing steel and concrete systems, where corroded steel could compromise the structural
system. FRP was considered as an alternative that could eliminate the corrosion problems which
deteriorate infrastructure. Some of the early projects using FRP included FRP bridge decks, and
bridges stressed with FRP tendons. Since then FRP has been used on existing structures to provide
seismic upgrade to bridges and buildings, increase strength, and provide resistance to corrosion and
chemicals when applied in the form of sheets. (16)

2.2 Composition and Properties
The two major components of FRP are fibers and resins. The fibers provide strength to the
FRP material, and the resins transfer stresses between the individual fibers, and provide chemical
resistance and anti-corrosive properties of FRP.

2.2.1 Fibers
Fibers provide structural strength to the FRP material. The fibers are individual strands
which have anisotropic material properties, in contrast to concrete and steel which are isotropic.
Isotropic materials have the same material properties independent of their orientation, and
anisotropic materials have material properties which vary across its axes. Fibers' strength properties
exist in the direction along its strands. These fibers are woven into different fabric patterns, which
can provide strength in a direction parallel to the length of the fabric, perpendicular to the length of
the fabric, or components in both directions by changing the direction of the fibers within the fabric.
The most commonly used fibers are glass, carbon, or amarid.

Glass fibers are the least expensive of the three materials, and carbon is the most expensive.
Glass fibers come in three different classes: E-glass, S-glass, and C-glass. E-glass is most commonly
used in infrastructure projects. Glass fibers have been tested and shown to creep under sustained
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loads, but it can be designed in a way to prevent this from occurring to a level which may become
problematic. Glass fibers have the lowest strength and lowest elongation capacities, and for those
reasons it is typically used for corrosion prevention rather than strength enhancements of existing
structures. It is made from raw materials that are plentiful, most notably sand, and therefore is a
sustainable product.

Table 1: Material Properties of Glass Fibers (Federal Highway Administration)

Density (g/cm5)

2.60

Young's Modulus (GPa)

2.50

; 72

I Tensile Strength (GPa)
Tensile Elongation (%)

87

1.72

2.53

2.4

2.9

Amarid fibers have high tensile strength and elastic modulus, excellent creep and shrinkage
resistance, and a lower density than glass or carbon fibers. Because of their elongation capabilities
they are good for impact. They are made synthetically, and extremely resistant to heat, fire,
chemicals, and corrosion.
Table 2: Material Properties of Amarid Fibers (Federal Highway Administration)

Density (g/cm3)
-

-

-

-

-

-

-

-

i 1.44

! 1.44

\

i

Young's Modulus (GPa)

83/100

124

Tensile Strength (GPa)

2.27

j 2.27

Tensile Elongation (%)

2.8

! 1.8

Carbon fibers have very high fatigue and creep resistance, and lower thermal expansion

coefficient than glass or amarid fibers. It is more brittle than glass or amarid. Usually high strength
carbon fibers are used for structural strengthening for flexure and shear. (11)

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Table 3: Material Properties of Carbon Fibers (Federal Highway Administration)

Density (g/cm3)

1.8

1.9

2.0 - 2.1

Young's Modulus (GPa)

230

370

520 - 620

Tensile Strength (GPa)

2.48

1.79

1.03 - 1.31

Tensile Elongation (%)

1.1

0.5

0.2

All of these fibers exhibit linear elastic behavior until their ultimate strength is reached. This
means that the material will behave elastically and then experience sudden brittle failure. FRP is not
ductile like steel and does not behave plastically. For this reason, most designs use allowable
strengths that are considerably lower than the ultimate strength of the fibers, but considering their
extremely high strengths, as high as 600 ksi, they are up to ten times stronger than a comparable
steel section. Therefore despite its brittle failure mechanism, FRP can still be a reliable design and
construction material due to its high strength, and ultimate strength which is much higher than that
of steel's plastic strength. When strength is desired more than deformation capacity, then a carbon
fiber can be used due to its high strength and lower ultimate strain capacity. When the deformation
capacity is desired as much as or more than the strength, such can be the case with seismic
retrofitting, an E-glass fiber can be used. (11)

s

E-glass (350 ksi)

V

£
V5
o
da

1

3,
fiber strain (%)

4

Figure 1: Stress-Strain Diagrams for Fibers (Federal Highway Administration)
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FRP for The Repair & Retrofit of Existing Structures & for New Construction

2.2.2 Resins
Fibers are saturated in resins. Resins help transfer stresses between the fibers, and protect
the fibers from damage such as UV rays, moisture, and chemical exposure. Two main types of resins
are thermosets and thermoplastics.

Thermoplastic resins are flowable when heated, and harden upon cooling. Thermoset resins
cure from being heated, from being part of a two part system with a catalyst reaction, or both. For
those reasons thermoset resins are used for composite materials. Different thermosets appropriate
for use in FRP are polyesters, phenolics, and epoxies.

Polyester Resins

Polyester resins were the first developed for use in composites. These resins are known for
their versatility. They provide a balance of corrosion resistance, non conductivity, low cost, and ease
of handling. Their properties can be modified by producers for specific projects, and are cost
efficient. This resin is good for its balance between performance and structural properties. (3)

Phenolic Resins

These resins are known for their ability to perform well in high temperature environments.
For this reason, these resins perform the best for fire resistance. They do not experience large
thermal movements, experience low creep, and have a high melting point. Additionally, they
provide excellent corrosion resistance, but are more expensive than polyester resins. (27)

Epoxy Resins

These resins generally have larger tensile strengths, greater bond strengths, and better
resistance to corrosion than Polyester Resins. They cure by a two part system, a resin and a
hardening catalyst. Once these are mixed together the mixture creates heat which begins the curing

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process. Epoxy resins generally take up to a full week to completely cure while Polyester resins will
cue within 6-8 hours. Epoxy resins will absorb less water than polyester resins. For reasons discussed
above, Epoxy resins have superior characteristics to Polyester Resins, but cost more. (12)

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FRP for The Repair & Retrofit of Existing Structures & for New Construction

3.0 FRP for Retrofit, Rehabilitation, & Repair of Existing Structures
FRP is a structural material which can be designed to provide reinforcement of sections for
flexure, shear, and confinement. Generally, concrete and steel can also be used to encase or
reinforce underperforming elements, but sometimes the additional weight of these materials causes
additional overstresses in the element being repaired or in the structure's foundation. FRP is
extremely lightweight compared to concrete and steel. It can reinforce overstressed elements
without adding additional considerable load to a structure, allowing for minimal impacts to the
existing structure's stability. Additionally, when an existing structure is prone to deterioration, an
FRP wrap used in conjunction with conventional repair methods can stop and prevent deterioration
from occurring within the section.

3.1 FRP for Tensile Reinforcement
FRP strips can be attached to the horizontal faces of flexural beams in order to provide
additional tensile capacity. In order to understand the mechanics of an FRP system, first the flexural
behavior of steel beams, and conventionally reinforced concrete beams must be understood.

3.1.1 Concept
When a moment is induced in a beam, across that beam's cross section both compressive
and tensile stresses are induced. The total induced tension equals the total induced compression.
For beams of uniform material, the stress at any given depth of the beam's cross section can be
calculated using the formula

CT =

M* c

-r

where M = the induced moment to the cross section, c = the distance from the beam's neutral axis,
and I = the cross section's moment of inertia. This formula holds true when the maximum stresses in

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the extreme fibers of the beam do not exceed their yield strength, therefore the beam still behaves
elastically.

With beam of a single material with a cross section that is symmetrical across its bending
axis, this results in a neutral axis at the beam's centerline, and equivalent compressive and tensile
stresses and strains in either side of the beam's cross section. Ductile materials like steel behave
well in tension and compression, as long as the possibility of buckling is prevented through the
design of adequate stiffeners spaced along the beam's length. A typical yield strength of steel is 60
kips per square inch, with some higher strength steels having yield strengths of 70 kips per square
inch. Brittle materials like concrete behave well in compression but have very limited tensile
capacity, and do not yield and instead crack. Concrete's maximum tensile stress is known as the
force of rupture, and is calculated, per 2010 AASHTO LRFD code as

fr = 7.5 4Tc

Where fc = the compressive strength of the concrete, in pounds per square inch. Concretes can have
variable strengths depending on mix proportions, but typical concrete strengths used in cast in place
structural construction are 3000 pounds per square inch (psi) to 4000 psi. For example, a 4000 psi
concrete has a force at rupture of only 150 psi. Considering the limited available tensile strength of
the concrete as compared to its compressive strength (150 psi, vs. 3000 psi) concrete beams
designed for flexure contain flexural reinforcement, typically steel. Important features of this steel

are its high tensile capacity, and its ductile properties to prevent brittle failure of the beam. An
engineer designs this steel to provide the beam's entire tensile capacity, without relying on the
concrete for tensile strength as it is a brittle material with very limited capacity in tension.

The flexure in a reinforced concrete beam is allowed by the balance of forces across the
cross section, with the total tension forces provided by the steel being completely counteracted by
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the compression of concrete on the other side of the beam's neutral axis. The moment capacity of
the cross section is calculated by multiplying the total available tensile capacity of the steel in the
beam (As*fy), by the distance between the centerline of the reinforcing steel, and the centerline of
the compression zone in the concrete (d - a/2). This number is usually factored, and as dictated by
current AASHTO LRFD codes, is multiplied by a factor of 0.9 for the beam's nominal moment
capacity.

Illustrative Example: Flexural Capacity of Conventionally Reinforced Concrete Section

h = total section depth; d = section depth minus the concrete covering the steel; fy = yield strength
of steel; b = width of base; As= area of steel

h = 24" Tall beam, d = 21"; b = 18"; fY= 60 ksi; fc = 4 ksi; As = 8 in2

T = Tensile Force = A s * f y
C = Compressive Force = 0.85 * /c' * b *a
EF = 0 ; therefore T = C
Solve for the depth to the neutral axis, a,

a

As* fy
0.85 * ft *b

8 in 2 * 60 ksi
0.85 * 4ksi * 18inches

tnc'ie5

M n = A s * f y (d - a/2) = 8 in 2 * 60 ksi * (21" - 7.84"/2) = 8197.6 k - in

3.1.2 Design Guidelines
Much like steel reinforcing bars are used in concrete beams to provide tensile capacity to
the section, FRP strips or panels may be used to provide additional tensile reinforcement to steel or
reinforced concrete beams. The strips are applied while saturated with resins to the outer face of

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the tension side of the beam. The panels are procured with resins, and are attached to a surface
with adhesives or mechanical anchors such as bolts. The tensile capacities of the panels and strips
are accounted for considering their strength per layer of fiber. (2)

Illustrative Example of a Concrete Beam with Steel Reinforcing bars and FRP Strips

n = number of layers of FRP laminate; fL = strength of FRP laminate; tL = thickness of one FRP
laminate layer; wL = width of applied laminate

h = 24" Tall beam, d = 21"; b = 18"; fY= 60 ksi; fc = 4 ksi; As = 8 in2; n = 1; fL= 350 ksi; tL= 1/16"; wL= b

T = Tensile Force = (/l s * f y ) + (n * t L * w L * f L )
C = Compressive Force = 0.85 * / c ' * b * a
IF = 0 ; therefore T = C

Solve for the depth to the neutral axis

(4> * f y ) + ( n * t L * w L * f L ) _ (8 in 2 * 60 ksi) + (1 * 1/16" * 18" * 350fcsQ
0.85 * 4ksi * Winches
0.85 * f c * b
= 14.28 inches
M„, steei = As* fy{d- a/2) = 8 in 2 * 60 ksi * (21" - 14.2872) = 6653.5 k-in

M n , FRP

= ( n * t L * w L * f t ) * ( h - a/2) = (1 * 1/16" * 18" * 350ksi) * (24" - 14.2872) =

6639.2 k - i n
Mn.

Total

=

6653.5 k - in + 6639.2 k - in = 13292.7 k - in

3.1.3 Construction and Application Methods
The existing surface must be cleaned and repaired before any FRP is applied. For steel, the

surface shall be blast clean. For concrete, any contamination and corrosion must be removed and
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repaired before application of FRP. This will remove and replace concrete and steel components
which can experience volumetric changes due to corrosion or alkali silica reactions. By mitigating
these volumetric changes, debonding of FRP from the beam's surface is prevented.

Once the existing beams have been sufficiently repaired typically a layer of adhesive is
applied to the surface, and then FRP can be installed. With FRP strips, the strips are typically
delivered to site impregnated with resins, or are impregnated with resins on site, also called "wet
layup" and then applied to the surface. Precast and cured panels are applied, and typically also
bolted or anchored in place to ensure adequate bond to the substrate. The exposed FRP strips and
panels should then have a UV protective coating applied, as FRP can degrade slowly with UV
exposure. After that application a layer of paint can be applied to the surface of the FRP to help it
blend in with the adjacent materials such as steel or concrete.

3.1.4 FRP for Flexure Case Studies
In 2002 in Denver Colorado a fire damaged the roof of an industrial plant. The fire damage
resulted in the permanent loss of strength in the concrete roofs reinforcing steel. In order to repair
the roof, the damaged cover concrete was removed using hydro-demolition, and was replaced using
shotcrete. The roofs existing condition was assessed using SAP finite element modeling, and the
flexural deficiencies in the roof were determined. FRP sheets were applied where negative moment
reinforcing was required on the peaks of the roofs, and where positive moment reinforcing was
required on the underside of the valleys of the roofs.(18)

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FRP for The Repair & Retrofit of Existing Structures & for New Construction

Figure 2: Industrial Plant with FRP Strips for Flexural Strength

Figure 3: Photos of Peaks and Valleys of Roofing with FRP Strips

East Church Street Bridge NYSDOT Cap Beam Strengthening Study

East Church Street Bridge in Elmira, NY was built in 1954. It is a four span bridge which
carries two lanes. In 1997 during an inspection it was found that the cap beams were exhibiting
cracking. This cracking is due to additional dead loads the structure has been loaded with since
construction. The deck now has an overlay, and concrete barriers whose dead loads were not
accounted for in the bridge's original design. NYSDOT used FRP plates to strengthen the structurally
deficient cap beam of its third pier for an evaluation of its performance and cost effectiveness. On
one side of the cap beam, plates were attached using epoxy layer and drilled anchor bolts into the
concrete cap beam. On the other side of the cap beam the panels were attached using the same
epoxy layer, and plates were applied and clamped to the FRP and concrete to ensure contact during

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FRPfor The Repair & Retrofit of Existing Structures & for New Construction

curing. After they were installed they got an application of tar coat to prevent water seepage
between the plates and concrete, and a layer of paint to resemble concrete and protect the FRP
from UV radiation.

After construction was completed, the structure was load tested, and the capacities of the
cap beams were found to have decreased the service load stresses in the negative moment

reinforcing steel by 10% and the positive moment steel by 6%. This study proved that FRP can be a
cost effective solution ($18,000) compared to conventional methods ($150,000), which can also be
easily installed, requiring limited lane closures. (25)

Shear pj
St|el girder (Typ.)

Positive moment
region plate (Typ.)

est
Bridge deck

East

Negative moment
region plate
vi

713 m

Beam:

Column:

Figure 4: FRP Plate Strengthening of Church Street Bridge Pier Cap

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FRPfor The Repair & Retrofit of Existing Structures & for New Construction

3.2 FRP Wrapping for Shear Reinforcement
Typical reinforced concrete column and beam design includes longitudinal steel reinforcing.
This longitudinal steel acts compositely with the concrete to provide flexural capacity to the section,
as previously discussed in section 3.1, FRP for Flexure.

Reinforced concrete section detailing also includes transverse reinforcing. This transverse
reinforcing can be in the form of hoops or continuous spiral reinforcing in circular cross sections in
columns. In rectangular sections, such as beams, the confinement is typically stirrups. For beams or
columns which are subject to shear, this transverse reinforcing contributes to the section's shear
capacity as described further below.

Figure 5: Photos of Typical Rebar Arrangements in Columns (Left) and Beams (Right)

3.2.1 Concept
Typically shear in a section is provided by the combined strength of the concrete and the
transverse steel. When a beam is subject to flexure, according to ACI code guidelines the concrete's
shear capacity is:
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FRPfor The Repair & Retrofit of Existing Structures & for New Construction

Vc = 2 * J f t * b w * d
The width of the base of the section is represented by bw. When a section is subject to
combined axial compression and flexure, according to the ACI, the shear resistance of the concrete
is calculated as:

Nu is the total axial force in the beam in pounds, and Ag is the gross cross sectional area in

square inches. When the applied shear in a section exceeds the concrete section's shear resistance,
then additional shear capacity is required. Conventionally this is achieved with transversely spaced
steel reinforcing bars. According to the ACI the shear capacity of transverse reinforcing is calculated
as:

A s * F y * d* (sina + cosa)

Where As = the cross sectional area of the shear reinforcing, Fy = the steel's yield stress, d = the
depth of the cross section in the dimension of the applied shear, s = the spacing of the transverse
reinforcing along the longitudinal axis of the beam, and a= the inclination angle of the reinforcing
within the beam, where reinforcing completely parallel to the direction of applied shear has an a of
90°. The total shear capacity of the section is the combined capacities of the steel and concrete
shear.

V T = VC + Vs

3.2.2 Design Guidelines
FRP strips can be applied to wrap a concrete beam to provide shear strength to the section.
The strips can be spaced incrementally, or applied continuously over the section's surface. FRP strips

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