Strengthening Analysis of RC Beam using (GFRP) … Prem Lata International Journal of Engineering Technology Science and Research IJETSR ISSN 2394 – 3386 Volume 4, Issue 6 June 2017

466 Prem Lata

International Journal of Engineering Technology Science and ResearchIJETSR

www.ijetsr.comISSN 2394 – 3386Volume 4, Issue 6

June 2017

Strengthening Analysis of RC Beam using (GFRP) Composite

Prem Lata

Department of Civil Engineering REC,Ambedkar Nagar (U. P.), India

*Prem lata, Assistant Professor, Department of Civil Engineering,, Rajkiya Engineering College, Ambedkar Nagar ( Uttar Pradesh),India

Abstract- FRP application is very effective way to repairand strengthen structures that have become structurallyweak over their life span. FRP repair system provide aneconomically viable alternative to traditional repairsystem and materials. worldwide, a great deal ofresearch is currently being conducted concerning the useof fibre reinforced plastic wraps, laminates and sheets inthe repair and strengthening of reinforced concretemember. Experimental investigation on the flexural andshear behaviour of RC beams strengthened usingcontinuous glass fibre reinforced polymer ( GFRP)sheets are carried out. Experimental data on load,deflection and failure modes of each of the beams whereobtained. The detail procedure and application of GFRPsheets for strengthening of RC beams is also include. Theeffect of number of GFRP layers and its orientation onultimate load carrying capacity and failure mode of thebeams are investigated.

Index Terms- RC Beam Construction Material, Castingof beam, Glass Fiber Reinforced polymer (GFRP),Matrix Materials, Strengthening of beams,Experimental Setup, fabrication of GFRP plate,Analysis of beam.

INTRODUCTION

The maintenance, Rehabilitation and upgrading ofstructural members, is perhaps one of the mostcrucial problem in civil engineering applications.Moreover, a large number of structures constructedin the past using the older design codes in differentparts of the world are structurally unsafe accordingto the new design codes. Since replacement of suchdeficient element of structures incurs a hugeamount of public money and time, strengtheninghas become the acceptable way of improving theirload carrying capacity and extending their serviceslives.

Structural strengthening may be required due tomany different situations.

Additional strength may be needed to allow forigher loads to be placed on the structure.

Strengthening may be needed to allow thestructure to resist loads that were not anticipated inthe original design.

Strengthening is required for loads resulting fromwind and seismic forces or to improve resistance toblast loading.

Additional strengthening may be needed due to adeficiency in the structure’s ability to carry theoriginal design loads.

The selection of most suitable method forstrengthening requires careful consideration ofmany factors including the following engineeringissues:

Operation constraints

Availability of materials, equipment andqualified contractors

Construction cost, maintenance costs and life-cycle costs

Load testing to verify existing capacity orevaluate new techniques and materials

Accessibility

Dimensional / clearance constraints

Magnitude of strength increase

Effect of project

Environmental conditions

In- place concrete strength and substrateintegrity.

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Ⅰ. RC BEAM CONSTRUCTION MATERIALFor construction of the RC beam using the mainlyas a construction material concrete, cement, sand,steel and water. These material provide flexural andtension strength of the RC beams or othercomponent of the structure. Their description isbelow:

CONCRETE

Concrete is a construction material composed ofPortland cement and water combined with sand,gravel, crushed stone or other material such asexpanded slag or vermiculite. Most structural workthe concrete is designed to give compressivestrength of 15 to 35 MPa. A concrete with trap rockmay have a density of 2,483 Kg/m³. Concrete isstronger in compression than in tension, and steelbar called rebar or mesh is embedded in structuralmember to increase the tensile flexural strength.The fine aggregate used in this investigation wasclean river sand, passing through 4.75 mm sievewith specific gravity of 2.68.The grading zone Ⅲ asper Indian standard specification. The maximumsize of coarse aggregate was 20 mm with specificgravity of 2.73.

For concrete, the maximum aggregate size usedwas 20 mm. nominal concrete mix of 1:1.5:3 byweight is used to achieve the strength of 20 N/mm². The water cement ratio 0.5 used. Three cubespecimen were cast and tested at the time of beamtest ( at the age 28 days ) to determine thecompressive strength of concrete. The averagecompressive strength of the concrete was 31 N/mm². Normally the full hardening period ofconcrete is at least 7 days. The gradual increase instrength is due to the hydration of the tri- calciumaluminates and silicates. sand in concrete wasoriginally specified as roughly angular, but roundedgrains are now preferred.

FINE AGGREGATE

Fine aggregate/sand is an accumulation of grain ofmineral matter derived from the disintegration ofrocks. Usually commercial sand is obtained fromriver beds or from sand dunes originally formed.

The most useful commercially are silica, sand oftenabove 98% pure. The weight varies from 1,538 to1,842 Kg/ m³, depending on the composition andsize of grain. The fine aggregate was passingthrough 4.75 mm sieve and had a specific gravity of

2.68. the grading zone of the fine aggregate waszone Ⅲ as per Indian standard specifications. Sandis used for making mortar and concrete and forpolishing and sandblasting. Sands containing a littleclay are used for making molds in foundries. Thefine aggregate obtained from river bed of koel, clearfrom all sorts of organic impurities was used in thisexperimental program.

COARSE AGGREGATE

Coarse aggregate are the crushed stone is used formaking concrete. the commercial stone is quarried,crushed and graded. Much of the crushed stoneused is granite, limestone and trap rock. The sizeare from 0.25 to 2.5 in (0.64 to 6.35cm), althoughlarger size may be used for massive concreteaggregate. Machine crushed broken stone angular inshape was used as coarse aggregate. The maximumsize of coarse aggregate was 20 mm and specificgravity of 2.78. granite is a coarse-grained, igneousrock having an even texture and consisting largelyof quartz and feldspar with often small amount ofmica and other minerals. the colors are usuallyreddish, greenish, or gray. The density is 2,723Kg/m³, the specific gravity 2.72 and the crushingstrength 158 to 220 MPa.

CEMENT –Cement is a material, generally in powder form,that can be made into a paste usually by theaddition of water, when molded or poured will setinto a solid mass. The most widely used of theconstruction cement is Portland cement. It is abluish- gray powder obtained by finely grinding theclinker made by strongly heating an intimatemixture of calcareous and argillaceous minerals.The chief raw material is mixture of high- calciumlimestone, known as cement rock, and clay or shale.Blast – furnace slag may also be used in somecement and the cement is called Portland slagcement (PSC). The specific gravity is at least 3.10Portland slag cement.

REINFORCEMENT

The longitudinal reinforcement used were high-yield strength deformed bars of 12 mm diameter.The stirrups were made from mild steel bars with 6mm diameter. The yield strength of steelreinforcements used in this experimental programwas determined by performing the standard tensiletest on the three specimens of each bar. The averageproof stress at 0.2% strain of 12mm Φ bars was 437

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N/mm² and that of 6 mm Φ bars was 240 N/mm².WATER

Water fit for drinking is generally considered fitfor making concrete. Water should be free fromacids, oils, alkalizes, vegetables or other organicimpurities. Soft water also poured weaker concrete.Water has two function in a concrete mix. Firstly, itreacts chemically with the cement to from a cementpaste in which the inert aggregates are held insuspension unit the cement paste has hardened.Secondly, it serves as a vehicle or individual in themixture of fine aggregate and cement.

Ⅱ. CASTING OF BEAMTwo set of beams were casted for this experimentaltest program. In SET Ⅰ three beams ( F1,F2 and F3)weak in flexural were casted using same grade ofconcrete and reinforcement detailing. In SET Ⅱthree beams (S1,S2 and S3) weak in shear werecasted using same grade of concrete andreinforcement detailing. the dimensions of all thespecimen are identical. The cross sectionaldimensions of the both the set of beams is 250 mmby 200 mm and length is 2300 mm. in SET Ⅰ beams2, 12 mm ᶲ bars are provided as the mainlongitudinal reinforcement and 6 mm ᶲ bars asstirrups at a spacing of 75 mm C/C where as in SETⅡ beams beam 3, 12 mm ᶲ bars are provided as themain longitudinal reinforcement and without anystirrups.

Fig. 1 Section of set Ⅰ beams

Fig 2: Section set Ⅱ beams

Material for Casting

(ⅰ) Cement- Portland cement (PSC)- 43 grade(kornak cement) was used for the investigation.

(ⅱ) Fine aggregate- the fine aggregate passingthrough 4.75 mm sieve and had a specific gravity of2.68.

(ⅲ) Coarse aggregate- the coarse aggregate usedwere of two grades, non- reactive and available inlocal quarry. One grade contains aggregates passingthrough 10mm and retained on 4.75mm sieve.Another grade contained aggregates passingthrough 20mm sieve but retained on 20 mm sieve.

(ⅳ) Water- Ordinary tap water for concrete mix inall mix

(ⅴ) Reinforcing steel- HYSD bars of 12 mm diawere used as main reinforcement. 6 mm dia mildsteel bars were used for shear reinforcement.

Form work

It should be strong enough to take the dead loadand live load, during construction and also it mustbe rigid enough so mat any building, twisting orsagging due to the load if minimized, woodenbeams, mild steel sheet, wood and any several othermaterials can also be used. The form work used forcasting of all the specimen consists of mouldprepared with two channel section of iron bolted byiron plates at the ends. The form work wasthoroughly cleaned and all the corners andjunctions were properly sealed by plaster of Paris toavoid leakage of concrete through small openings.Shuttering oil was then applied to the form work

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carefully keeping in view a clear cover of 20mm forthe top and bottom bars.

Mixing of Concrete

Mixing of concrete should be done thoroughly toensure that concrete of uniform quantity isobtained. Hand mixing is done in small work, whilemachine mixing is done for all big and importantwork. Turn the dry materials at least three timesuntil the colour of the mixture is uniform. Addwater slowly while you turn the mixture again atleast three times, or until you obtain the properconsistency. Usually 10% extra cement is added incase of hand mixing to account for inadequacy inmixing.

Compaction

All specimens were compacted by using needlevibrator for good compaction of concrete.Sufficient care was taken to avoid displacement ofthe reinforcement cage inside the form work.Finally the surface of the concrete was levelled andfinished and smoothened by metal trowel andwooden float.

Curing of Concrete

The concrete is cured to prevent or replenish theloss of the water which is essential for the processof hydration and hence for hardening. Also curingprevent the exposure of concrete to a hotatmosphere and to drying winds which may lead toquick drying out of moisture in the concrete andthereby subject it to contraction stress at a stagewhen the concrete would not be strong enough toresist them. Concrete is usually cured by wateralthough scaling compounds are also used.

Ⅲ.. FIBER REINFORCED POLYMER (FRP)

Fiber reinforced polymer (FRP) is a compositematerial made by combining two or more materialsto give a new combination of properties. Themechanical and physical properties of FRP arecontrolled by its constituent properties and bystructural configurations at micro level. FRPcomposite is a two phases material, hence itsanisotropic properties. It is composed of fiber andmatrix, which are bonded at interface.

Fig 3: Formation of fiber reinforced polymercomposite

FIBER

A fiber is a material made into a long filament witha diameter generally in the order of 10 tm. Theaspect ratio of length and diameter can be rangingfrom thousand to infinity in continuous fiber. Themain function of the fiber are to carry the load andprovide stiffness, strength, thermal stability andother structural properties in the FRP.

To perform these desirable functions, The fiber inFRP composite must have:

ⅰ) high modulus of elasticity for use as reinforcedⅱ) high ultimate strengthⅲ low variation of strength among fiber

ⅳ) high stability of their strength during handlingⅴ) high uniformity of diameter and surfacedimension among fiber.

Types of fiber used in fiber reinforced polymercomposites

Glass fiber

Carbon fiber

Aramid fiberMaterial Density

(g/cmᶾ)Tensile

Modulus

(E)(GPa)

Tensilestrength(GPa)

Specificmodulus

Specificstrength

Relativecost

E- glass 2.54 70 3.45 27 1.35 Low

S- glass 2.50 86 4.50 34.5 1.8 Moderate

Graphit,highmodulus

1.9 400 1.8 200 0.9 High

Graphit,Highstrength

1.7 240 2.6 140 1.5 High

Boron 2.6 400 3.5 155 1.3 high

Kevlar29

1.45 80 2.8 55.5 1.9 Moderate

Kevlar49

1.45 130 2.8 89.5 1.9 moderate

Table 1: properties of different fiber

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ⅰ) glass fibersTheir peculiar characteristic is their high strength.Glass is mainly made of silicon ( Sio₂) with atetrahedral structural ( Sio₄). Some aluminumoxides and other metallic ions are then added invarious proportion to either ease the workingoperations or modify some properties ( e.g, S-glassfiber exhibit a higher tensile strength than E- glass)

E-glass S-glassSilicon oxide 54.3 64.20Aluminumoxide

15.2 24.80

Iron oxide - 0.21Calcium oxide 17.2 0.01Magnesiumoxide

4.7 10.27

Sodium oxide 0.6 0.27Boron oxide 8.0 0.01Barium oxide - 0.20Various - 0.03

Table 2: Typical composition of fiber glass (% inweight)

ⅱ) CARBON FIBERCarbon fiber consist of small crystallite ofturbotratic graphite. These resemble graphite singlecrystals except that the layer planes are not packedin a regular fashion along the c-axis direction. Thesingle crystals are highly anisotropic with the planemodule of the order of 100 GPa whereas themolecules perpendicular to the basal plane are onlyabout 75 GPa. they have lower thermal expansioncoefficients than both the glass and aramid fibers.The carbon fiber is an anisotropic material, and itstransverse modulus is an order of magnitude lessthan its longitudinal modulus. As a result of thisphenomenon, carbon composite laminates are moreeffective with adhesive bonding that eliminatesmechanical fasteners.

Typical density young modulus Tensile strengthTensile

Properties (g/cm³) ( GPa) (GPa) Elongation

(%)

High Strength 1.8 230 2.48 1.1

High Modulus 1.9 370 1.79 0.5

Ultra – High 2.0-2. 1 520-620 1.03-1.31 0.2

Modulus

ⅲ) ARAMID FIBERIt is also very heat resistant and decomposes above400˚ C without melting. It was inveted by Stephaniekwolek of dupont from research into highperformance polymer, and patented by her in 1966and first marketed in 1971. Aramid or kelvarmolecules have polar group accessible for hydrogenbonding. Water that enters the interior of the fibercan take place of bonding between molecules andreduce the materials strength, while the availablegroups at the surface lead to good wettingproperties. This is important for bonding the fiberto other types of polymer, forming a fiberreinforced plastic. This same property also makesthe fiber feel more natural and “sticky” compared tonon- polar polymer like polyethylene. In structuralapplication, kelvar fiber can be bonded to oneanother or to other material to form a composite.Kelvar main weaknesses are that it decomposesunder alkaline conditions or when exposed tochlorine. While have a great tensile strength,sometimes in excess of 4.0 GPa, like all fiber ittends to bickle in compression.

Fig 3: structure of aramid fiber

Ⅳ. TYPES OF MATRIX MATERIAL

Fiber, since they cannot transmit loads from one toanother, have limited use in engineeringapplication. When they are embedded in a matrixmaterial, to form a composite, the matrix serves tobind the fiber together, transfer loads to the fiber,and damage due to handling. The matrix has astrong influence on several mechanical propertiesof the composite such as transverse modulus andstrength, shear properties, and properties incompression. Physical and chemical characteristicsof the matrix such as melting or curing temperature,viscosity, and reactivity with fiber influence thechoice of fabrication process.

Commonly used matrix materials are-

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ⅰ) Epoxy resinEpoxy resins are relatively low molecular weightpre- polymers capable of being processed under avariety of conditions. Two important advantages ofthese resins are over unsaturated polyester resinsare: first, they can partially cured and stored in thatstate, and second they exhibit low shrinkage duringcure. Epoxy resins are characterized by thepresence of a three- member ring containing twocarbons and an oxygen ( epoxy group or epoxide oroxirane ring). Epoxy is the first liquid reactionproduct of bisphenol- A with excess ofepichlorohidrin and this resins is known asdiglycidylether of bisphenol A ( DGEBA).

Fig 4- Structure of DGEBA

The primary and secondary amines are reactivecuring agents. the primary amino group is morereactive towards epoxy than secondary amino groupare consumed(95%), whereas only 28% ofsecondary amino group are consumed.

Fig. 5 The curing of epoxy resin with primaryamines

The composite materials constitute 3-9% of totalstructural weight of the commercial aircrafts suchas Boeing 767 or Boeing 777. Composite andlaminate industry uses 28% of epoxy resinsproduced.

Property

Density, g/cm³ 1.2-1.3

Tensile modulus, MPa 55-130

Tensile modulus, GPa 2.75-4.10

Thermal expansion,10ˉ⁶/˚C

45-65

Water absorption, % in24h

0.08-0.15

Table 3: Properties of epoxy resin

The resin and hardener are used in this study isaraldite LY 556 and hardener HY 951, respectively.Araldite LY_ 556, an unmodified epoxy resin basedon bisphenol- A and the hardener ( ciba- geig,india) HY 951 ( 8% of total epoxy taken) analiphatic primary amine, were mixed properly.Properties Araldite

LY556HardenerHY951

Color clear ColorlessOdor Slight AmmoniaPhysical liquid LiquidSolubility inwater

insoluble Miscible

Vapor pressure <0.01Pa at20˚C

<0.01 mmHgat 20˚C

Specific gravity 1.15-1.2 at25˚C

1 at 20˚C

Boiling point >200˚C >200˚CDecompositionTemperature

>200˚C >200˚C

Table 4: Properties of epoxy resin and hardener

ⅱ) Unsaturated polyester resinsUnsaturated Polyesters are long- chain linearpolymer containing a number of carbon doublebonds. They are made by a condensation reactionbetween a glycol ( ethylene, propylene, diethyleneglycol) and an unsaturated dibasic acid. A typicalpolyester resin made from reaction of maleic acidand diethylene glycol is shown below:

HOOC-CH=CHCOOH+[HOCH2CH2OCH2OH]→OH-[CH2CH2OCH2OC-OCH=COHCO]n-H+H2O

The length of the molecule or degree ofpolymerization n may vary. The resin will generallybe a solid but is dissolved in a monomer such asstyrene. The solution viscosity can be controlled bythe percent styrene and is generally quite fluid.

Property

Density, g/cm³ 1.1-1.4

Tensile strength, MPa 24.5103.5

Tensile modulus,GPa 2-4.4

Thermal expansion, 10ˉ⁶/˚C 55-100

Water absorption, %in 24h 0.15-0.6

Table 5: typical properties of cast thermosettingpolyesters

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ⅲ) Adhesives

The implementation of FRP- based structuralstrengthening requires the use of adhesives. thechoice of the most suitable adhesives as well as thetype of surface treatment to be carried out prior toFRP application shall be made on the basis ofavailable substrate and properties of the selectedFRP system. Technical data sheet for FRP materialsusually report the indication of the adhesive to beused as a function of the structure to bestrengthened.

An adhesive is a material quite often of apolymeric nature capable of creating a link betweenat least two surface and able to share loads. Thereare many types of natural and synthetic adhesives (elastomers, thermoplastic, and mono- or bi-component thermosetting resins) the most suitableadhesive for composite materials are based onepoxy resins.

Ⅴ. STRENGTHEING OF BEAM

Before bonding the composite fabric onto theconcrete surface, the required region of concretesurface was made rough using a coarse sand papertexture and cleaned with an air blower to remove alldirt and debris. Once the surface was preparedrequired standard, the epoxy resin was mixed inaccordance with manufacturer’s instructions.Mixing was carried out in a plastic container andwas continued until the mixture was in uniformcolour. When this was completed and the fabricshad been cut to size, the epoxy was applied to theconcrete surface. The composite fabrics was thenplaced on top of epoxy resin coating and the resinwas squeezed through the roving of the fabric withthe roller. Air bubbles entrapped at the epoxy/concrete or epoxy/ fabric interface were to beeliminated. Than the second layer of the epoxyresin was squeezed through the roving of the fabricwith the roller and the above process was repeated.During hardening of the epoxy, a constant uniformpressure was applied on the composite fabricssurface in order to extrude excess epoxy resin andto ensure good contact between the epoxy, theconcrete and the fabric. This operation is carriedout at room temperature. Concrete beamsstrengthened with glass fibre fabrics were cured for24 hours at room temperature before testing.

Fig. 8: Application of epoxy and hardener on thebeam

Fig 6: Fixing of GFRP sheet on the beam

Fig 7: Roller used for removal of air bubbles

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Ⅵ. EXPERIMENTAL SETUP

After the curing period of 28 days was over, thebeam as washed and its surface was cleaned forclear visibility of cracks. The most commonly usedload arrangement for testing of beams will consistof two-point loading. This has advantage of asubstantial region of nearly uniform momentcoupled with very small shears, enabling thebending capacity of the central portion to beassessed. If the shear capacity of the member is tobe assessed, the load will normally be concentratedat a suitable shorter distance from a support.

The specimen was placed over the two steel rollersbearing leaving 150 mm from the ends of the beam.The remaining 2000mm was divided into threeequal parts of 667 mm as shown in fig. Two pointloading arrangement was done. Loading was doneby hydraulic jack of capacity 100 KN. Threenumber of dial gauges were used for recording thedeflection of the beams. One dial gauge was placedjust below the centre of the beam and the remainingtwo dial gauges were placed just below the pointloads to measure deflections.

fig 9 : two point loading experiment setup

Fig 10: shear force and bending moment diagramfor two point loading

Fig10:shear strengthening zone and flexurestrengthening zone beam

Fig 11: Experimental setup for testing of beams

Ⅶ) FABRICATION OF GFRP PLATE

The industry has evolved oven a dozen separatemanufacturing processes as well as a number ofhybrid processes. each of these processes offersadvantages and specific benefits which may applyto the fabrication of composites. Hand lay-up andspray-up are two basic moulding processes. Thehand lay-up process is the oldest, simplest, andmost labour intense fabrication method. In handlay-up method liquid resin is placed along withreinforcement (woven glass fibre) against finishedsurface of an open mould. Chemical reaction in theresin harden the material to a strong, light weightproduct. The resin serves as the matrix for thereinforcing glass fibres, much as concrete acts asthe matrix for steel reinforcing rods. The

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percentage of fibre and matrix was 50:50 in weight.The following constituent materials were used forfabricating the plate:

1-E-glass woven roving as reinforcement

2-Epoxy as resin

3-Hardener as demine (catalyst)

4-Polyvinyl alcohol as a releasing agent

Contact moulding in an open mould by hand lay-upwas used to combine piles of woven roving in theprescribed sequence. Flat plywood rigid platformwas selected. A plastic sheet was kept on theplywood platform and a thin film of polyvinylalcohol was applied as a releasing agent by use ofspray gun. Laminating stars with the application ofa gel coat (epoxy and hardener) deposited on themould by brush, whose main purpose was toprovide a smooth external surface and to protect thefibres from direct exposure to the environment. Plywas cut from roll of woven roving. Layers ofreinforcement were placed on the mould at top ofthe gel coat and gel coat was applied again bybrush. Any air which may be entrapped wasremoved using serrated steel rollers. The process ofhand lay-up was the continuation of the aboveprocess before the gel coat had fully hardened.Again, a plastic sheet was covered the top of plateby applying polyvinyl alcohol inside the sheet asreleasing agent. Then, a heavy flat metal rigidplatform was kept top of the plate for compressingpurpose. The plates were left for a minimum of 48hours before being transported and cut to exactshape for testing.

Fig 12: Specimen for tensile testing in INSTRON1195

Fig 13: Experimental setup of INSTRON 1195

Fig 14: specimen failure after tensile test

RESULT

The ultimate stress, ultimate load and young’smodulus are determined experimentally byperforming unidirectional tensile tests on specimenscut in longitudinal and transverse direction, and at45˚ to the longitudinal direction, as described inASTM standard: D638-08 and D 3039/D3039M-2006. A constant rectangular cross section wasprepared in all cases. The dimension of thespecimen was taken as below:

Length(mm) Width(mm) Thickness(mm)

200 24 0.6

Table 6: Size of the specimen for tensile test

The specimen were cut from the plates themselvesby diamond cutter or by hex saw after cutting in thehex saw, it was polished in the polishing machine.At least three replicate sample specimens weretested and mean values adopted.

Coupons were machined carefully to minimize anyresidual stresses after they were cut from the plateand the minor variation in dimensions of differentspecimens are carefully measured. For measuring

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the young’s modulus, the specimen is loaded inINSTRON 1195 universal testing machinemonotonically to failure with a recommended rateof extension (rate of loading) of 5 mm/minute.Specimen were fixed in the upper jaw first and thengripped in the movable jaw 9lower jaw). Grippingof the specimen should be as much as possible toprevent the slippage. Here, it was taken as 50mm ineach side. Initially strain was kept at zero. The load,as well as the extension, was recorded digitally withthe help of a load cell and an extensometerrespectively. From these data, engineering stress vs.Strain curve was plotted,

The initial slope of which gives the young’smodulus. The ultimate stress and ultimate load wereobtained at the failure of the specimen.

Ultimatestress (MPa)

Ultimateload (KN)

Young’modulus(MPa)

GFRP plateof 2- layers

334.5 4.817 11310

Table 7: ultimate stress, ultimate load and young’smodulus of GFRP plate

Ⅷ. STRENGTHENING ANALYSIS OF BEAM

FLEXURAL STRENGTHEING OF BEAMS

To increase flexural strength, FRP fabrics arebonded as an external reinforcement on the tensionside of steel- reinforced concrete beams with fibreorientation along the member length. Depending onthe ratio of FRP reinforcement are to the beamacross- sectional area and the area of internal steelreinforcement, the increase in flexural strength canbe more than 100%. However, a flexural strengthincrease up to 50% would be more realistic, whichdepends on practical consideration such as theconcrete member dimension, serviceability limits,ductility and effective thickness of FRP fabricreinforcement.

Fig 15: Area for flexural and shear strengthening ofbeams

Elevation Section A-AFig 16: Flexural strengthening of beam using FRP

sheet at the bottom

ASSUMPTION

1-Design calculation are based on the actualdimensions, internal reinforcing steel arrangementand material properties of the existing memberbeing strengthened.

2-The strains in the reinforcement and concrete aredirectly proportional to the distance from theneutral axis.

3-There is no relative slip between external FRPreinforcement and the concrete

4-The shear deformation within the adhesive layeris neglected since adhesive layer is very thin withslight variations in its thickness.

5-The maximum usable compressive strain in theconcrete is 0.003.

6-The tensile strength of concrete is neglected

7-The FRP reinforcement has a linear elastic stress-strain relationship to failure.

Fig 17: Stress Strain diagram of singly reinforcedbeam strengthen with FRPCALCULATION OF MOMENT OFRESISTANCE OF THE BEAMSThe moment of resistance of the set I beams areobtained from the following calculation:grade of concrete 30,grade of steel 415 width ofbeam 299mm depth of beam 415mmAs per IS: 456:2000, clause 38.1, ANNEX G,Total force due to compression = Total force oftension0.36 Fck b Xm (d-0.42Xm) = 0.87 Fck Ast (d-0.42Xm)

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Using this formula fined neutral axis and momentresistanceNeutral axis is the 36.59mm and moment ofresistance is 17.12KN-m.Now considering the effect of strengthening ofbeam F2 using two layers of GFRP sheets, sp alongwith the tensile force an addition tensile force willbe also acting. The value of obtained from theexperimental testing.Neutral axis is 54.54mm and moment of resistanceis 24.6 KN-mThe depth of neutral axis and the moment ofresistance of both the beams is.

Beam mm KN-mF1 36.59 17.12F2 54.54 24.6

Table 7: Analytical calculation of beams F1 and F2

RESULT

Two set of beams were tested for their ultimatestrengths. In set I three beams weak in flexural aretested. In set Ⅱ three beams weak in shear aretested. It was observed that the beams F1 and S1had less load carrying capacity when compared tothat of the externally strengthened beams usingGFRP sheets.

Sr.no

Types ofbeam

Beamdesignation

Load atinitialcrack(KN)

Ultimateload(KN)

Nature offailure

1

Beamsweak inflexural(set1)

F1

F2

F3

30

34

Notvisible

78

104

112

Flexural failure

GFRP rupture+ flexural-shear failure

GFRP rupture+ flexure –shear failure

2 Beamsweak inshear (set Ⅱ)

S1

S2

S3

35

39

40

82

108

122

Shear failure

Flexural failure+ crushing ofconcrete

Flexural failure+ crushing ofconcrete

Table 8: ultimate load and nature of failure for set1and set2 beams

ULTIMATE LOAD CARRYING CAPACITY

The load carrying capacity of the control beamsand the strengthen beams were strengthen found outand shown in fig.

Fig 18: Load at initial crack of beam F1,F2 and F3.

Fig 19: Ultimate load of beams S1, S2 and S3

COMPARISON OF RESULT

The failure mode, load at initial crack and ultimateload of the control beams without strengthening andthe beams strengthen with two layer GFRP sheetare presented.

SET I BEAMS Fromanalytical study

Fromexperimentalstudy

F1 17.12 KN-m 26.00 KN-m

F2 24.60 KN-m 34.68 KN-m

Table 9: comparison of value obtained fromanalytical and experimental study

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CONCLUSIONS

In this experiment investigation the flexural andshear behaviour of reinforced concrete beamsstrengthened by GFRP sheets are studied. Initialflexural cracks at a higher load by strengthening thebeam at soffit.

Set I beams F1,F2 and F3 is initial flexural appearat a higher load by strengthening the beam at soffit.The ultimate load carrying capacity of thestrengthen beam F2 is 335 more than the controlledbeam F1. The ultimate load carrying capacity of thestrengthen beam f3 is 43 5 more than the controlbeam F1 and &% more than the strengthen beamF2. Analytical analysis is also carried out to findthe ultimate moment carrying capacity andcompared with the experimental results. In set Ⅱbeams S1, S2 and S3 is the control beams S1 failedin shear as it was made intentionally weak in shear.The initial crack in the strengthen beam S2 and S3appears at higher load compared to the un-strengthen beam S1. The ultimate load carryingcapacity of the strengthen beam S2 is 31% morethan the controlled beam S1. When the beam isstrengthen by U- wrapping in the shear zone, theultimate load carrying capacity is increased by 48%compared to the control beam S1 and by 13%compared the beam S2 strengthen by bonding the

GFRP sheet on the vertical side alone in the shearzone of the beam.

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Documents

Strengthening Analysis of RC Beam using (GFRP) … Prem Lata International Journal of Engineering Technology Science and Research IJETSR ISSN 2394 – 3386 Volume 4, Issue 6 June 2017