FLEXURAL BEHAVIOUR OF RC BEAM WRAPPED WITH GFRP...

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International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 2, February 2017, pp. 452–469 Article ID: IJCIET_08_02_048

Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=2

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

© IAEME Publication Scopus Indexed

FLEXURAL BEHAVIOUR OF RC BEAM WRAPPED

WITH GFRP SHEETS

T.P. MEIKANDAAN

Research Scholar, Dept of Civil Engineering,

Bharath University, Chennai, Tamilnadu, India

Dr. A. RAMACHANDRA MURTHY

*Senior Scientist CSIR -Structural Engineering Research Centre

Taramani, Chennai-113, Tamil Nadu, India

ABSTRACT

Repair and strengthening of R.C beam is now becoming more and more important in the field of

structural strengthening and retrofitting. The present paper reviews the study of Glass Fiber

Reinforced Polymer (GFRP) flats under flexural behavior in reinforced concrete beams. In this study,

experimental investigation on the flexural behavior of RC Beam has been studied by wrapping Glass

Fiber Reinforced Polymer (GFRP) sheets. Reinforced Concrete Beam externally bonded with GFRP

sheets were tested to failure using a symmetrical two point static loading system. Six Reinforced

Concrete Beams have been cast for this experimental test. All cast beams are weak in flexural and

having same reinforcement detailing. Three beams are used as control beams and three beams are

strengthened using full bottom of glass fiber reinforced polymer (GFRP) sheets. The experimental

result shows, that full bottom GFRP sheet wrapping in 70% preloaded beam can increase flexural

capacity of the beam by 14%(on ultimate load) as compared to Controlled Beams.

Key words: Glass Fibre Reinforced Polymer, Concrete Beams, Flexural Strengthening, Deflection.

Cite This Article: T.P. Meikandaan and Dr. A. Ramachandra Murthy, Flexural Behaviour of RC

Beam Wrapped with GFRP Sheets. International Journal of Civil Engineering and Technology, 8(2),

2017, pp. 452–469.

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=2

1. INTRODUCTION

1.1. GENERAL

Reinforced cement concrete is an extremely popular construction material used for structural components of

a building like beams, columns and slabs etc. One major flaw of RCC is its susceptibility to environmental

attack. This can severely decrease the strength and life of the structures. The repair of structurally deteriorated

RC Structures become necessary since the structural element ceases to provide satisfactory strength and

serviceability. Some of these structures are in such a bad condition that they need to be replaced. Two

T.P. Meikandaan and Dr. A. Ramachandra Murthy


techniques are typically adopted for the strengthening of beams, relating to the strength enhancement desired:

flexural strengthening or shear strengthening. In many cases it may be necessary to provide both strength

enhancements. For the flexural strengthening of a beam, FRP sheets or plates are applied to the tension face

of the member (the bottom face for a simply supported member with applied top loading or gravity loading).

Principal tensile fibers are oriented in the beam longitudinal axis, similar to its internal flexural steel

reinforcement. This increases the beam strength and its stiffness (load required to cause unit deflection),

however decreases the deflection capacity and ductility.

1.2. BACKGROUND

A large number of structures constructed in the past using the older design codes in the different parts of the

world are structurally unsafe according to the new design codes. Since replacement of such deficient elements

of structures incurs a huge amount of public money and time, strengthening has become the acceptable way

of improving the load carrying capacity and service lives. Wrapping Techniques of Flexural concrete

elements is traditionally accomplished by externally bonding steel plates to concrete. Although this technique

has proved to be effective in increasing strength and stiffness of RC Beam, it has the disadvantages being

susceptible to corrosion and difficulty in installation.

Recent developments in the field of composite materials together with their inherent properties which

include high tensile strength, good fatigue strength, corrosion resistance, ease of use make them an alternative

to the steel plates in the field of repair and strengthening of concrete beams.

For the past studies conducted it has been shown that externally bonded glass fiber reinforced polymers

(GFRP) can be used to increase or enhance the Flexural Strength, shear strength, and torsional capacity of

RC beams.

1.3. AIM

The major aim of the project is to study the behavior of R.C.C. beams retrofitted with GFRP overlays so that

to obtain best procedures for strengthening of R.C.C. beams using GFRP overlays. To improve the load

carrying capacity of the R.C.C Beam using GFRP overlays is the aim of the project

1.4. OBJECTIVES

1. To study the ductility of flexural deficient beams

2. To study the effect of different sized layers of GFRP, which can be wrapped on both shear deficient beams and

flexural deficient beams

3. To compare the strength of various layers of GFRP which can be wrapped on beams

1.5. SCOPE OF STUDY

The investigations as well as studies conducted on the retrofitting of the RCC beams using Glass Fiber

reinforced polymer overlays are limited. So it is essential to study the shear carrying capacity, Flexural

carrying capacity and ductility of flexural beams by retrofitting with GFRP.

1.6. FACTORS TO BE CONSIDERED FOR STRENGTHENING OF BEAMS:

• Magnitude of strength increase

• Effect of change in relative member stiffness

• Size of the project

Flexural Behaviour of RC Beam Wrapped with GFRP Sheets


1.7. APPLICATION OF GFRP OVERLAYS FOR STRENGTHENING OF RC BEAMS

1.7.1. Fiber Reinforced Polymer (FRP)

Fiber reinforced polymer (FRP) composites are formed by embedding continuous Fibers in a resin matrix

that binds the Fibers together.

1.7.2. Types of FRPs

Depending on the Fibers used, FRP composites are classified into three types: Glass FRP composites (GFRP),

Carbon FRP composites (CFRP) and Aramid FRP composites (AFRP).

Although FRP composites are expensive and more susceptible to physical damage than steel, they have

become an attractive substitute for steel in strengthening systems for concrete structures due to their many

advantages, high strength to weight ratio, corrosion resistance, High fatigue resistance, easy and reliable

surface preparation.

1.7.3. FRP Composite

Fiber Reinforced Polymer composite is defined as a polymer (plastic) matrix, either thermo set or

thermoplastic, that is reinforced (combined) with a fiber or other reinforcing material with a sufficient aspect

ratio(length to thickness) to provide a discernable reinforcing function in one or more directions

1.7.4. GFRP Sheets

Application of GFRP overlays is the one of the simplex methods for wrapping the existing structures. GFRP

has high strength ratio high stiffness to weight ratio, flexibility in design, non corrosiveness, high ultimate

strength and lower density.

1.8 ADVANTAGES AND LIMITATIONS OF GFRP OVERLAYS FOR

STRENGTHENING OF BEAMS

1.8.1 Advantages

1. Low cost when compared to other FRPs

2. High Strength to weight ratio

3. Corrosion resistance

1.8.2. Disadvantages

1. The main disadvantage of externally strengthening structures with Composite materials is the risk of fire,

vandalism or accidental, damage, unless the strengthening is protected.

2. Compressive strength is lower than tensile strength.

3. The lack of experience of the techniques and suitably qualified staff to

1.10. GFRP WRAPPING PROCESS

While doing the wrapping process, first the beams were washed with acetone to remove the dust, dirt and

were made clean. The surfaces of the beams were rubbed with paper to make the surface rough. Then

wrapping of GFRP sheets on the surface of the beams were done. The wet lay up or hand layup technique

will be adopted. Concrete beams strengthened with glass Fiber fabric were cured for 48 hours at room

temperature before testing.



1.11. Epoxy adhesives

• Strong adhesive to bonded elements.

• Strong cohesion.

• Little tendency to creep under load.

2. LITERATURE REVIEW

2.1. INTRODUCTION

This section deals with the study of investigations done on applications of Fiber Reinforced Polymer (FRP)

plates especially GFRP overlays used for strengthening of reinforced concrete beams. Investigations were

done by wrapping GFRP over lays to the RCC beams and tested for load carrying capacity of beams.

2.2. SUMMARY OF LITERATURE

From the above literature review it is observed that by use of GFRP overlays there is the considerable increase

in flexural strength. The ultimate load carrying capacity of retrofitted flexural deficient beams was improved

by 5% to 20% depending upon the number of layers and type of overlays and in the case of shear deficient

beams it varies from 2.5% to 15% depending upon the number of layers and type of overlays. These

deficiencies occurs due to several reasons such as insufficient shear reinforcement or reduction in steel, due

to corrosion, increased due to load and due to construction defects therefore to reduce or to minimize these

deficiencies externally bonded reinforcement such as Glass Fiber Reinforced Polymer is an excellent solution

in these situation.

3. METHODOLOGY

3.1. Flow Chart



3.2. MATERIALS

3.2.1. Cement

Portland Pozzolona Cement (PPC)-53 grade was used for the investigation. It was tested for its physical

properties in accordance with Indian Standard specifications.

3.2.2. Fine Aggregate

The sand used for experimental program was locally procured and conforming to zone II. The sand was first

sieved through 4.75 mm sieve to remove any particles greater than 4.75 mm. It was tested as per Indian

Standard Specification IS: 383-1970. The specific gravity coarse aggregate are 2.6

3.2.3. Coarse Aggregate

Locally available coarse aggregates were used in this work. Aggregates passing through 20mm sieve and

retained on 16mm sieve were sieved and tested as per Indian Standard Specifications IS: 383-1970. The

specific gravity coarse aggregate are 2.65

3.2.4. Water

The tap water available in the campus was tested for its suitability. Necessary properties such as pH value,

chloride content, total hardness and total dissolved solids were evaluated.

3.2.5. Reinforcing Steel

HYSD bars of 8 mm φ were used as main reinforcement. 6 mm φ mild steel bars were used for shear

reinforcement.

3.2.6. Fiber Reinforced Polymer (FRP)

Continuous fiber-reinforced materials with polymeric matrix (FRP) can be considered as composite,

heterogeneous, and anisotropic materials with a prevalent linear elastic behavior up to failure. They are

widely used for strengthening of civil structures. There are many advantages of using FRPs:

lightweight, good mechanical properties, corrosion-resistant, etc. Composites for structural

strengthening are available in several geometries from laminates used for strengthening of members with

regular surface to bidirectional fabrics easily adaptable to the shape of the member to be strengthened.

3.2.6.1. Glass fiber

Glass fibers are also available as thin sheets, called mats. A mat may be made of both long continuous and

short fibers (e.g., discontinuous fibers with a typical length between 25 and 50 mm), randomly arranged and

kept together by a chemical bond. The width of such mats is variable between 5 cm and 2 m, their density

being roughly 0.5 kg/m2. Glass fibers typically have a Young modulus of elasticity (70 GPa for E-glass)

lower than carbon or aramid fibers and their abrasion resistance is relatively poor; therefore, caution in their

manipulation is required. In addition, they are prone to creep and have low fatigue strength. To enhance the

bond between fibers and matrix, as well as to protect the fibers itself against alkaline agents and moisture,

fibers undergo sizing treatments acting as coupling agents. Such treatments are useful to enhance durability

and fatigue performance (static and dynamic) of the composite material. FRP composites based on fiberglass

are usually denoted as GFRP.

3.2.7. Resin

Epoxy resin is used for wrapping the specimens with GFRP.



3.2.7.1. Epoxy Adhesive

The Sikadur 30 epoxy resin is a thixotropic adhesive mortar, based on a two-component solvent free epoxy

resin. The mixing ratio was 3:1 of Component A (resin) and Component B (hardener) by weight. The elastic

modulus, tensile strength, and shear strength as provided by the manufacturer are 11.7 GPa, 24.8 MPa, and

15 MPa, respectively.

3.2.9. Accelerator

It is used along with catalyst to harden the resin from liquid states to solid states.

3.2.9. Catalyst

Catalyst increases the rate of a chemical reaction of two or more reactants and helps in rapid hardening of the

mix

3.2.10. Pigment

A pigment is a material that changes the colour of mix. White pigment is used for wrapping the specimens

with GFRP.

3.3. TEST PROGRAM

3.3.1.

In nominal mix concrete, properties of ingredients are not considered and same is limited up-to M20 grade

only. For present work, Portland Pozzolana Cement (PPC) was used in nominal and design mixed M20 grade

concrete and required angular aggregate and zone III river sand, nominal mix concrete (1.0 : 1.60: 2.75) was

prepared. Density and cement content of fresh concrete were 2217.00 kg/m3 and 413 kg/m3 respectively.

3.3.2. PREPERATION OF MOULD

Fresh concrete, being plastic requires some kind of form work to mould it to the required shape and also to

hold it till it sets. The form work has, therefore, got to be suitably designed. It should be strong enough to

take the dead load and live load, during construction and also it must be rigid enough to withstand any

bulging, twisting or sagging due to the load.

4. EXPERIMENTAL SETUP AND TESTING

4.1. EXPERIMENTAL SETUP

Six specimens are prepared for this experiment using cement, fine aggregate and coarse aggregate for which

the designs mix proportion is arrived. To investigate the ultimate load carrying capacity of beam, specimens

are prepared and designated as follows.

• CB– Control Beam specimens 3 for flexural.

• Wrapped beam – Beam specimen with bottom full layer of GFRP for 70% preloading.

Preliminary tests are carried as per IS standard on the material used for concrete like specific gravity,

fineness, consistency, and initial setting time for cement. For fine and coarse aggregates tests such as sieve

analysis, specific gravity, impact value, crushing value and abrasion value (Los Angeles) are conducted as

per standards and results are tabulated.



The ingredients of concrete such as cement, fine aggregate, coarse aggregate of maximum nominal size

of 20mm are weighed accurately using the platform weighing machine. The ingredients are mixed manually

and adequate amount of water is added to the constituents of concrete.

4.1.1. Casting of Specimen

The dimension of the beam specimens to be prepared is 1500mm x 200mm x 100mm as shown in figure

specimens has to be casted for this experiment using M20 grade of concrete. A standard curing will be done

for 28 days after the casting of specimens.

Figure 4.1.1. Typical diagram of beam dimension

4.1.2. Wrapping of Specimen with GFRP

Glass fiber reinforced polymer will be wrapped in bottom full layers at the length of the beam specimen. Out

of 6 specimens, 3 specimens will be used as control beam specimen and the rest 3 will be wrapped with

GFRP in bottom full layer in the specimen.

Figure 4.1.2 Wrapping of beam specimen

4.2. Testing of Specimen

The specimens will be tested to find the ultimate load carrying capacity and displacement of beam specimens.

4.2.1. Form work

Fresh concrete, being plastic requires some kind of form work to mould it to the required shape and also to

hold it till it sets. The form work has, therefore, got to be suitably designed. It should be strong enough to

take the dead load and live load, during construction and also it must be rigid enough so mat any bulging,

twisting or sagging due to the load if minimized, Wooden beams, mild steel sheets, wood, and several other

materials can also be used. Formwork should be capable of supporting safely all vertical and lateral loads

that might be applied to it until such loads can be supported by the ground, the concrete structure, or other

construction with adequate strength and stability. Dead loads on formwork consist of the weight of the forms

and the weight of and pressures from freshly placed concrete. Live loads include weights of workers,

equipment, material storage, and runways, and accelerating and braking forces from buggies and other

placement equipment.

Figure 4.2.1.B Reinforcement setting



4.2.2. Mixing of Concrete

Mixing of concrete should be done thoroughly to ensure that concrete of uniform quantity is obtained. Hand

mixing is done in small works, while machine mixing is done for all big and important works. Although a

machine generally does the mixing, hand mixing sometimes may be necessary. Use either a hoe or a square-

pointed D-handled shovel to mix the materials. Turn the dry materials at least three times until the color of

the mixture is uniform. Add water slowly while you turn the mixture again at least three times, or until you

obtain the proper consistency. Usually 10% extra cement is added in case of hand mixing to account for

inadequacy in mixing.

Figure 4.2.2 Mixing of Concrete

4.2.3. Compaction

All specimens were compacted by using needle vibrator for good compaction of concrete. Sufficient care

was taken to avoid displacement of the reinforcement cage inside the form work. Finally the surface of the

concrete was leveled and finished and smoothened by metal trowel and wooden float.

Figure 4.2.3 Concrete Mould

4.2.4. Curing Of Concrete

The concrete is cured to prevent or replenish the loss of water which is essential for the process of hydration

and hence for hardening. Also curing prevents the exposure of concrete to a hot atmosphere and to drying

winds which may lead to quick drying out of moisture in the concrete and thereby subject it to contraction

stresses at a stage when the concrete would not be strong enough to resists them.

Figure 4.2.4 Curing of Beams

4.3. EXPRERIMENTAL SETUP IN LABORATORY

All the specimens were tested in the loading frame of the “Structural Engineering” Laboratory Bharath

University, Chennai. The testing procedure for the entire specimen was same. After the curing period of

28 days was over, the beam as washed and its surface was cleaned for clear visibility of cracks. The most

commonly used load arrangement for testing of beams will consist of two-point loading. This has the



advantage of a substantial region of nearly uniform moment coupled with very small shears, enabling the

bending capacity of the central portion to be assessed. If the shear capacity of the member is to be

assessed, the load will normally be concentrated at a suitable shorter distance from a support. The

specimen was placed over the two steel rollers bearing leaving 150 mm from the ends of the beam. The

remaining 1200 mm was divided into three equal parts of 400 mm as shown in the figure. Two point

loading arrangement was done as shown in the figure. Loading was done by hydraulic jack of capacity

20 Tone. Two number of dial gauges LVDT1 and LVDT2 were used for recording the deflection of the

beams. The two dial gauges were placed just below the point loads to measure deflections.

Figure 4.3.A Two point loading experimental setup

Figure 4.3.B SEI – 3 Nos Control Beam Figure 4.3.C Control beams setup

4.4. EXPERIMENTAL PROCEDURE

Before testing the member was checked dimensionally, and a detailed visual inspection made with all

information carefully recorded. After setting and reading all gauges, the load was increased incrementally up

to the calculated working load, with loads and deflections recorded at each stage. Loads will then normally

be increased again in similar increments up to failure, with deflection gauges replaced by a suitably mounted

scale as failure approaches. This is necessary to avoid damage to gauges, and although accuracy is reduced,

the deflections at this stage will usually be large and easily measured from a distance. Similarly, cracking

and manual strain observations must be suspended as failure approaches unless special safety precautions are

taken. If it is essential that precise deflection readings are taken up to collapse. Cracking and failure mode

was checked visually, and a load/deflection plot was prepared.



Figure 4.4.A Deflection recording machine (LVDT) Figure 4.4.B Electrical load cells for recording of applied load.

4.4.1. Testing of Control Beams

Table 4.4.1 Control beams testing reading details

BEAM NO F2 F10 F19

Initial Crack Load 20 kN 15 kN 20 kN

Ultimate Load 60 kN 60 kN 60 kN

Load in kN

LVD1 in

mm

LVD2 in

mm

LVD1 in

mm

LVD2 in

mm

LVD1 in

mm

LVD2 in

mm

0 0 0 0 0 0 0

5 0.3 0.1 0.2 0 0.2 0.2

10 0.5 0.2 0.5 0.2 0.4 0.4

15 0.8 0.5 1.1 0.6 0.6 0.5

20 1.3 0.9 1.7 0.9 1 0.9

25 1.8 1.3 2.3 1.2 1.5 1.4

30 2.3 1.8 2.9 1.6 2.1 2

35 2.9 2.2 3.5 2.1 2.5 2.4

40 3.4 2.5 4.1 2.5 3.2 3

45 4 3 5.5 4 3.8 3.5

50 5.3 4 7.6 5.6 5 5

55 7.9 5.6 10.3 8.5 7 7

60 12 10.6 16.6 15.6 10.5 11.2

58 13.3 12 17.3 16.5 11.8 12.8

55 14.3 12.5 17.8 17 12.7 14

50 17 13 18.3 17.5 14 15.4

45 18.5 14 19 18 15.3 16.2

40 19 15.3 19.8 18.7 17.2 18

35 20.5 16.2 20.5 19.2 18 19

30 21 17.1 21 20.5 19 20.2

4.4.1.1. Crack portion of flexural control beam

Figure 4.7.1.1 Crack Portion of Flexural Control Beam



4.4.1.2. Load vs deflection grape for control beams

Figure Load Vs Deflection Curve for Control Beam # F2 Figure Load Vs Deflection Curve for Control Beam # F1

0Figure c Load Vs Deflection Curve for Control Beam # F19

4.5. STRENGTHENING OF BEAMS

Before bonding the composite fabric onto the concrete surface, the required region of concrete surface was

made rough using a coarse sand paper texture and cleaned with an air blower to remove all dirt and debris.

Once the surface was prepared to the required standard, the epoxy resin was mixed in accordance with

manufacturer’s instructions. Mixing was carried out in a plastic container (Araldite LY 556 – 100 parts by

weight and Hardener HY 951 – 8 parts by weight) and was continued until the mixture was in uniform colour.

When this was completed and the fabrics had been cut to size, the epoxy resin was applied to the concrete

surface. The composite fabric was then placed on top of epoxy resin coating and the resin was squeezed

through the roving of the fabric with the roller. Air bubbles entrapped at the epoxy/concrete or epoxy/fabric

interface were to be eliminated. Then the second layer of the epoxy resin was applied and GFRP sheet was

then placed on top of epoxy resin coating and the resin was squeezed through the roving of the fabric with

the roller and the above process was repeated. During hardening of the epoxy, a constant uniform pressure

was applied on the composite fabric surface in order to extrude the excess epoxy resin and to ensure good

contact between the epoxy, the concrete and the fabric. This operation was carried out at room temperature.

Concrete beams strengthened with glass fiber fabric were cured for 24 hours at room temperature before

testing.



Figure 4.5.A 70% Flextural Pre loading Beam

Figure 4.5.B Clean up with salt paper Figure 4.8.C Sika 30 epoxy resin mixing

Figure 4.5.C GFRP Laminate sheet fixing with sika grow

Figure 4.5 D Flextural 70 % Preloading GFRP Bottom full Wrapping Beam Setup



4.8.1. Testing of Flexural Bottom Full Wrapping Beams

Table 4.8.1 Flexure bottoms full GFRP Sheet wrapping after pre-loading beams testing reading details

BEAM NO F21 F22 F23

Initial Crack Load 20 kN 20 kN 25 kN

ULTIMATE LOAD FOR

CONTROL BEAM 60 KN 60 KN 60 KN

ULTIMATE LOAD FOR

70 % PRE LOADING 42 kN 42 kN 41 kN

GFRP WRAPPING

POSITION IN

FLEXTURAL

BOTOM FULL LENGTH BOTOM FULL LENGTH BOTOM FULL LENGTH

Load in kN LVD1 in

mm

LVD2 in

mm

LVD1 in

mm

LVD2 in

mm

LVD1 in

mm

LVD2 in

mm

0 0 0 0 0 0 0

5 0.2 0.5 0.5 0.8 0.2 0.1

10 0.4 1 0.8 1 0.8 0.3

15 0.7 1.5 1 1.5 1.2 0.6

20 1.2 2.2 1.4 1.8 1.6 0.9

25 1.7 3 1.9 2.2 2.2 1.3

30 2.3 3.7 2.4 3 2.8 1.7

35 2.9 3.9 2.9 3.5 3.2 2.3

40 3.5 4.2 3.4 4 3.7 2.7

45 3.7 4.6 3.6 4.6 4.5 3

50 4.2 5.3 4 5.2 5.3 3.5

55 4.9 6 4.6 5.7 6.2 4.3

60 5.1 6.5 5.2 6.2 8.7 6

65 6.2 7.2 5.9 6.6 9.5 7.2

70 7 7.9 7 7 10.2 8.5

65 10 9 8 9 12.5 9

60 11.2 11 9.2 10.7 13.6 9.8

55 12.2 12 10.5 13 14.7 10.5

50 13 13 11.6 15.5 15.8 11.2

45 13.5 15 12.8 17 17 12.3

40 14.2 17 13.5 19 17.7 13.5

30 15.1 19 15 21 18.8 15

20 16 22 18 23 22 17

ULTIMATE LOAD FOR

WRAPPING BEAM 70 KN 65N 70 KN

% OF INCREASE 16.67 8.33 16.67

Avg % Increase 14 %



Fig Load vs Deflection curve for Flexural Full Bottom Wrapping Beam No: 21 Fig b Load vs Deflection curve for

Flexural Full Bottom Wrapping Beam No: 22

Fig4.8.1.1.c. Load vs Deflection curve for Flexural Full Bottom Wrapping Beam No: 23

5. RESULTS AND DISCUSSION

5.1. INTRODUCTION

This chapter describes the experimental results of SET I beams (Control Beam) and SET II beams (weak in

flexure). Their behavior throughout the static test to failure is described using recorded data on deflection

behavior and the ultimate load carrying capacity. The crack patterns and the mode of failure of each beam

are also described in this chapter. Three sets of beams were tested for their ultimate strengths. In SET I three

beams (beam no F2, F10 and F19) were tested for their ultimate strengths. In SET II three beams (beam nos

are F21, F22 and F23) were tested for 70% of pre ultimate load are tested. SET II beams F21, F22 and F23

after pre loaded using GFRP laminate sheet is strengthened only at the bottom of the beam in the flexure

zone of the beam. Deflection behavior and the ultimate load carrying capacity of the beams were noted. The

ultimate load carrying capacity of all the beams along with the nature of failure is given in Table 6.2.

5.2. FAILURE MODES

The following flexural failure modes should be investigated for an FRP-strengthened section:

• Crushing of the concrete in compression before yielding of the reinforcing steel; Strengthening of Reinforced

Concrete Beams using Glass Fiber Reinforced Polymer

• Yielding of the steel in tension followed by rupture of the FRP laminate;

• Yielding of the steel in tension followed by concrete crushing;

• Shear/tension delamination of the concrete cover (cover delamination); and

• Debonding of the FRP from the concrete substrate (FRP debonding).

A number of failure modes have been observed in the experiments of RC beams strengthened in flexure

by GFRPs. Flexural failure due to GFRP rupture and crushing of concrete at the top. Concrete crushing is

assumed to occur if the compressive strain in the concrete reaches its maximum usable strain. Rupture of the

FRP laminate is assumed to occur if the strain in the FRP reaches its design rupture strain before the concrete

reaches its maximum usable strain. Cover delamination or FRP debonding can occur if the force in the FRP

cannot be sustained by the substrate. In order to prevent debonding of the FRP laminate, a limitation should

be placed on the strain level developed in the laminate. The GFRP strengthened beam and the control beams

were tested to find out their ultimate load carrying capacity. It was found that the control beams F2, F10, &



F19 showing that the beams were deficient in flexure.. In SET II beams F21,F22 and F3, GFRP rupture and

flexural kind of failure was prominent when strengthening was done using the wrapping schemes.

Table 5.2 Ultimate load and nature of failure for SET I and SET II beams

Sr.No Type of

Beam

Beam

designation

Load at

initial crack

(KN)

Wrapping

position Ultimate

Load (KN)

Nature of

failure

1 Control

Beams

F2 20 - 60 Flexural

failure F10 15 - 60

F10 20 - 60

2

Beams

weak in

flexure

F21 20 Bottom full (

70 %

Preloading)

70 Flexural

failure +

Crushing of

concrete

F22 20 65

F23 25 70

5.3. LOAD DEFLECTION HISTORY

The load deflection history of all the beams was recorded. The deflection of each beam was compared with

that of their respective control beams. Also the load deflection behavior was compared between wrapping

schemes having the same reinforcement. It was noted that the behavior of the flexure deficient beams when

bonded with GFRP Laminates sheets were better than their corresponding control beams. The deflections

were much lower when bonded externally with GFRP Laminates sheets. The graphs comparing the deflection

of flexure deficient beams and their corresponding control beams are shown in Chapter 4 Figs 4.7.1.a to

4.7.1.c, & 4.8.1.a to 4.8.1.c. The use of GFRP sheet had effect in delaying the growth of crack formation. In

SET II when the wrapping schemes were considered it was found that the beam F21,F22 and F23 with Bottom

full wrapping of GFRP sheet had a better load deflection behavior when compared to the Set I control beam

F2,F10 and F19.

5.3.1. Loads At Initial Crack

Two point static loading was done on both SET I and SET II beams and at the each increment of the load,

deflection and crack development were observed. The load at initial crack of all the beams was observed,

recorded and is shown in & Fig 5.3.1.a & 5.3.1.b. Fewer than two point static loading of SET I beams, at

each increment of load, deflection and crack development were observed. In beam F2 & F10, initiation of

the crack takes place at a load of 20 KN. In F19 beam initiation of the crack takes place at a load of 15 KN.

In SET II Beam the crack initiation of the beam F21, & F22 was takes place at a load of 20 KN., and F23

initiation of the crack takes place at a load of 25 KN.

Figure 5.3.1.a Initial crack Curve for Control Beams Figure 5.3.1.b Initial crack Curve for Wrapping Beams



5.3.2. Ultimate Load Carrying Capacity

The load carrying capacity of the control beams and the strengthen beams were found out and is shown in

fig 5.3.2.a and 5.3.2.b. The control beams were loaded up to their ultimate loads. It was noted that of all 3

beams, the strengthen beams F21, F22 and F23, had the higher load carrying capacity compared to the

controlled beams F2,F10 &F 19 . Important character to be noticed about the usage of GFRP sheets is the

high ductile behavior of the beams. But the ductile behavior obtained by the use of GFRP can give us enough

warning before the ultimate failure. The use of FRP can delay the initial cracks and further development of

the cracks in the beam.

Figure 5.3.2.a Ultimate load for Control Beams Figure 5.3.2.b Ultimate load for Wrapping Beams

5.4. CRACK PATTERN

The crack patterns at collapse for the tested beams of SET I and SET II are shown in Fig.5.4. In SET I the

controlled beams are F2, F10 and F19 exhibited widely spaced and lesser number of cracks compared to

strengthened beams F21, F22 and F3. The strengthened beams F21, F22, and F23 have also shown cracks at

relatively close spacing. This shows the enhanced concrete confinement due to the GFRP strengthening. This

composite action has resulted in shifting of failure mode from flexural failure (steel yielding) in case of

controlled beam.

Figure 5.4 Crack Pattern for flexural Beams

5.5. COMPARISION OF RESULTS

The results of the two set of beams tested are shown in Table 4.7.1 & 4.8.1. The Table 5.1 shows that

failure mode, load at initial crack and ultimate load of the control beams without strengthening and the beams

strengthen with flexural bottom full GFRP sheet are presented.

The 70% damage degree beams increases load carrying capacity 14% when strengthened with 100 mm

width of 1.5m beam and 1.2mm thick of GFRP sheet in bottom full layer as compared with control beam



6. CONCLUSIONS

In this experimental investigation the flexural behavior of reinforced concrete

beams strengthened by GFRP sheets are studied. Two sets of reinforced concrete (RC)

beams, in SET I three beams for control beams weak in flexure and in SET II three beams damaged beams

strengthened by GFRP laminated sheets. From the test results and calculated strength values, the

following conclusions are drawn:

1. Initial flexural cracks appear at a higher load by strengthening the beam at soffit.

2. The ultimate load carrying capacity of the strengthened beam is 14 % more than the controlled beam.

3. Analytical analysis is also carried out to find the ultimate moment carrying capacity

and compared with the experimental results. It was found that analytical analysis

predicts lower value than the experimental findings.

4. Flexural strengthening up to the neutral axis of the beam increases the ultimate load

carrying capacity, but the cracks developed were not visible up to a higher load. Due

to invisibility of the initial cracks, it gives less warning compared to the beams

strengthen only at the soffit of the beam.

5. By strengthening up to the neutral axis of the beam, increase in the ultimate load

carrying capacity of the beam is not significant and cost involvement is almost three times compared to the

beam strengthen by GFRP sheet at the bottom only.

6. Use of FRP laminate improves load carrying capacity; delays crack formation and energy absorption capability

of beam reinforced with FRP laminates.

7. The 70% damage degree beams increases load carrying capacity 14% when strengthened with 100 mm width

and 1.2mm thick of GFRP sheet in single layer for bottom full as compared with control beam

6.1. SCOPE OF THE FUTURE WORK

• It promises a great scope for future studies. Following areas are considered for future research

• Strengthening of beam weak in shear.

• Effect on torsional strength due to retrofitting

• Developing a non linear finite element model for the analysis of the strengthened RC

• Beams using various configuration of FRP strengthening.

• Variation of beam dimension.

• Strengthening of Beam with different type of FRP (like Carbon fiber reinforced polymer),

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