strengthening of rc beam using gfrp wraps

7/27/2019 Strengthening Of RC Beam Using GFRP Wraps

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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013

ISSN: 2231-5381 http://www.ijettjournal.org Page 1527

Strengthening Of RC Beam Using GFRP Wraps

T.Manikandan1. G.Balaji ponraj

2

1Assistant Professor in Civil Engineering, PSNA College of Engineering and Technology, Dindigul, Tamilnadu.

2

Assistant Professor

in Civil Engineering, PSNA College of Engineering and Technology, Dindigul, Tamilnadu.

Abstract - Fiber reinforced polymer materials arecontinuing to show great promise for using strengthening

reinforced concrete structures. These materials are an

excellent option for use as external reinforcing, because of

their light weight, resistant to corrosion and high strength.

The main aim of this study is to investigate the flexural

characteristic ofRC beams using GFRP sheets and strips.

This paper presents experimental results of the RC

beams strengthened in flexure with various externally

bonded GFRP configurations, here in order to delay theGFRP debonding as well as to increase the efficiency of theGFRP strips, additional U jacket strip or sheets

located in the debonding initiation region have been

proposed. Ten rectangular RC specimens were tested to

evaluate the effect ofusing the additional U shaped GFRP

sheets and spaced U strips on the intermediate

crack debonding of the laminate. The fiber orientation

effects of the side bonded sheets were also investigated.

The beam specimens to be rehabilitated are initially

loaded to 75% of estimated ultimate load, treated and

tested to failure. The parameters consider for the study

are ultimate load carrying capacity load deflection

failure modes and flexural stiffness of the strengthenedbeams.

I. INTRODUCTIONThe strengthening of concrete structures with

externally bonded reinforcement is generally doneby using either steel plates or Fibre ReinforcedPolymer (FRP) laminates. Each material has its

specific advantages and disadvantages. The platebonding technique is now established as a simpleand convenient repair method of enhancing theflexural, shear and compressive performance ofconcrete structures. Fibre reinforcedpolymers offer numerous

beneficial characteristics over steel includingexcellent corrosion resistance, non magnetic, nonconductive, generally resistant to chemicals, goodfatigue resistance, low coefficient of thermal

expansion, and high strength to weight ratio as wellas being lightweight. FRPs also possess a highspecific stiffness and an equally high specific strength in the

direction of fibre alignment. Use ofFRPs provides a high structural efficiency and theirlow density makes physical implementation much

easier. Unfortunately, FRPs are also expensive, but

the higher costs of FRP materials are often offset bysavings in reduced periodic maintenance, longer life

spans and ofreduced labour costs.

II. CONCRETE

For concrete the maximum aggregate size usedwas20 mm. the concrete mix proportion designed by ISmethod to achieve the strength of 20 N/mm2 and

was 1: 1.62:3.8 by weight. the design water cement

ratio was 0.55. Three cube specimens were cast andtested at the time of beam test (at the age of 28days) to determine the compressive strength of concrete. Theaverage compressive strength of theconcrete was 30N/mm2.

III. REINFORCING STEELThe yield of steel reinforcement used in this

experimental program was determined byperforming the standard tensile test on threespecimens of each bar diameter. The average yield

stresses of steel bars were 400 N/mm2 for 10 mm

diabar.

IV. EPOXY RESINThe success of the strengthening technique critically

depends on the performance of the epoxy resin

used. These epoxies are generally a two partsystems, a resin and a hardener. The resin andhardener used in this study were Araldite GY 257

and Hardener HY 840 respectively. The propertiesof epoxy resin and hardener supplied by themanufacturer are summarized in Table 1.

V.TENSILE TEST ON FIBRE COMPOSITES

To determine the tensile tests on composites,different resin to fibre ratios and thicknesses ofGFRP were cast. Tensile tests were conducted asper the ASTM D 638 - 1968.The tensile test

specimen is shown in figure.3 and the optimumresin to fibre ratio was found.


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Table.l - Properties of Epoxy Resin andHardener

VI. FRP LAMINATES

Fibre reinforced polymer material systemscomposed of fibre embedded in a polymeric matrix,exhibit several properties which create the

opportunity for their use as structural reinforcing

elements. They are characterized by excellenttensile strength in the direction of the fibers. FRPcomposites do not exhibit yielding, but instead are

elastic upto failure. They are also characterized byrelatively low modulus of elasticity in tension andlow compressive properties. FRP composites arecorrosion resistant and should perform better thanother construction materials in terms of weathering

behavior. In this study, bidirectional glassreinforced polymerlaminate are used.

Table.2 Properties of FRP

VII. BONDING PROCEDURE

Before bonding the composite fabric onto theconcrete surface, special consideration was given to

the surface preparation. The concrete surface was slightlygrinded off to remove material forenhancing good bonding and cleaned with airblower to remove all dirt and debris. Once the

surface hadbeen prepared to the requiredstandard, the epoxyresin had to be mixed in accordance withmanufacturer's instructions. Mixing was carried outin a metal container (Araldite GY 257 - 100 partsby weight and Hardener HY 840 - 50 parts by

weight) and was continued until the mixture was ofa uniform colour. When this was completed, the

epoxy resin was applied to the concrete surface. Theresin mixture flowed and filled the cracks bygravity. After bonding of FRP to concrete plastic sheets

were wrapped tight around the FRP to enhance theconfinement. Over the plastic sheets weights were

applied to ensure good bonding and removal ofentrapped air from the confinement of FRP. After a

curing time of 2-3 days, the rehabilitated specimenswere tested until failure. The cracking pattern,ultimate loads and deflected shape of the specimenswere noted.

VIII. TESTING FOR BEAMSA two-point flexure bending system was adopted

for the tests. All the beams were designed to fail

flexure only, premature failure by shear wasavoided by providing adequate number of stirrups at2D distance from both ends, after mounting the test

beams over two supporting pedestals kept at the twoends, the concentrated loads consisting the twopoint loading scheme was applied by means of SOT

hydraulic jack, using distributor made of steel boxsection. For measurements of deflection, dialgauges were located at three places, one at mid span

and other two under the load points. At the end ofeach loadincrement, observations were recorded for under loaddeflection, midpoint deflection, crack development and its

propagation on the beam surfaces. The load at first crack,ultimate load, type of failure etc., were carefullyobservedand recorded

IX.TEST SPECIMENSThe tests were carried out on ten simply supported

reinforced concrete beams with square cross sectionof 150* 150 anda span length of 1000 mm. The beams werestrengthened with external U wraps

bonded to to tension side. The continuous GFRPreinforcement which give delay in debonding of

S.NO Properties AralditeHardenerHY 840

1Density at25C

g/cm3

1.15 0.98

2Specificgravity

1.8 2.0

3

Flectural

strengthKg/cm

2450-550 300-400

PROPERTIES E-GLASS

Density of fiber 2.6 x lO-5N/mm3

Fiberthickness 0.3mm

Tensile strength 3450N/mm2

Tensile modulus 62000 N/mm2


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bottom longitudinal GFRP laminates. In this out of ten beamstwo were controlled specimen, two beams were treated ascontinuous U jacketed wraps, two beams were treated as

partially U jacketing wraps, remaining four beams weretreated and GFRP strips were bondedat different spacing.

X. CRACK PATTERN

The crack concentration area was located in thepure bending region. The application of GFRPcontinuous U - shaped sheets caused a shifting ofthe cracked region towards the supports. Due to the

utilization of the side- bonded sheets in the beams,it was not possible to monitor the crack pattern ofthe beams.

XI. LOAD TO DEFLECTION BEHAVIOUR

The load carried by tested beams for all groups ofbeams at initial and ultimate load levels. The initialloadwas taken at which the deflection ofthe control beams

was measured at above 35% of their ultimateload. The initial crack fore the control beams was

about 12 kN and the corresponding deflection at thelevel was about 0.35 mm. The ultimate loadobtained is higher for fully and partially wrapped

beams as comparedto controlledbeams.

XII. COMPARISON OF LOAD VS DEFLECTION

The increase in load carrying capacity ofrehabilitated beams proves the effectiveness of thestrengthened system in upgrading the RC beam

capacity. The test result indicates that the beamsstrengthened with GFRP laminates have more loadcarrying capacity as compared to controlledspecimen. This can be attributed to the high tensile strength


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and modulus of elasticity of GFRP laminates. Theeffectiveness of bonded externalreinforcement becomes more apparent, when

compared to control specimen. As a result theproportion, increase in strength with control beamwas less than that obtainedin the GFRP wraps.

XIII. FAILURE MODESNormally two failure modes are possible with the

FRP externally strengthened reinforced concretebeams: (i) rupture of frp laminates on the bottom of

the beam 2.crushing of concrete at the top of thebeam. both failure modes occur after considerableflexural cracking andvertical deflection. The mode of failurewas found flexure zone as load increased

higher. These cracks gradually increase in heightwith an increase in load.

XIV. CONCLUSIONThis research work included the testing of ten

reinforced concrete beams, each having a span of 1000 mmand strengthened in flexure using various

externally bonded GFRPconfigurations based on thespecific findings of this research , the followingconclusions may be drawn

1. For all of the tested specimens, the mode of thefailure was characterized by intermediate crackdebonding of the bottom FRP flexuralstrengthening reinforcement.

2. Using an additional transverse FRP continuous U- wrap

system with the fibre direction parallelto the beam axis, increase the ultimate load carryingcapacity, mainly because of the

flexural contribution of the GFRPreinforcement.

3. There was a significant effect of the width ofthe flexural GFRP laminates on the debonding

mechanism. In the case of the narrow laminates, the debonding plane was observed inside the

concrete cover, along the steel reinforcement.4. Not extending the length of the U - shaped

distance to cover the ends of the laminateslimited the effectiveness of 'the anchorage

techniques as far as the ultimate load capacitieswere concerned.

XV. REFERENCES

[1.] Azadeh Parvin and Wei Wang (2001) "Behavior

of FRP jacketed concrete columns under eccentric

loading ", Journal of composites for construction,

voI.5,ppI46-152

[2.] Balasubramanian.K, Krishnamoorthy.T.S,

BharatkumarB.H , Udhayakumar.V and

Lakshmanan.N (2007) "Investigations on the RC

Structural Elements Retrofitted Using FRP

Wraps", Journal Of Structural Engineering ,vol.

34,pp 63-69.

.

[3.] Bisby.L.A, Green.M.F, and Kodur.K.R (2005) "

Modeling the behavior of Fiber Reinforced

Polymer- confined concrete columns exposed to

fire " , Journal of composites for' construction,

vol.9,ppI5-24.

[4.] Bonacci.J.F and Maalej.M (2000) "Externally

bonded FRP for service life extension of RCinfrastructure", Journal of Infrastructure systems,

vot-e,pp 41-51.

[5.] Dimitri Val.V (2003) " Reliability of Fiber

Reinforced Polymer confined concrete columns

" Journal of composites for construction, vo129,

ppI122-1130.

[6.] Lacobucci.D, Shamin Sheikh.A , and Oguzhan

Bayrak " Retrofit of square concrete columns with

Carbon Fiber-Reinforced Polymer for seismic

resistance "ACI Structural Journal , vol. I 00 ,pp

785-794 .

[7.] Lam.L and TengJ.G (2002) "Strength Models for.

Fiber-Reinforcedl'lastic-Confined Concrete "

Journal of structural engineering, vol. 128, pp 612-

623.[8.] Matthys.S, Toutanji.H and Taerwe.L (2006),

"Stress-Strain Behavior of Large-Scale Circular

Colunms Confined with FRP Composites",

Journal of Structural Engineering, Vol. 132, No.t,

pp.t23-133.

[9.] Ming-Hung Teng,; Elisa Sotelino.D; and WaiFah

Chen " Performance Evaluation of Reinforced

Concrete Bridge Columns Wrapped with Fiber Reinforced

Polymers" Journal of composites for construction, vol.79, pp83-92.

strengthening of rc beam using gfrp wraps

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