EXPERIMENTALSTUDY ON STRENGTHENING OF RC BEAMS USING GLASS FIBERG.Swarnalakshmi1AssistantProfessor, New Prince ShriBhavani College of Engineering and Technology, Chennai – 600 073ABSTRACT- This paper presents the use of fiberreinforced plastic wraps, laminates and sheets in the repair and strengthening of reinforced concrete members.Fiber-reinforced polymer (GFRP)application is a very effective way to repair and strengthened structures thathave become structurally weak over their life span. Experimental investigationson the flexural and shear behavior of RC beams strengthened using continuousglass fiber reinforced polymer (GFRP) sheets are carried out. Externallyreinforced concrete beams with epoxy-bonded GFRP sheets were tested to failureusing a symmetrical two pointconcentrated static loading system, experimental data on load, deflection andfailure modes of each of the beams were obtained. The detail procedure andapplication of GFRP sheets for strengthening of RC beams is also included. Theeffect of number of GFRP layers andits orientation on ultimate load carrying capacity and failure mode of thebeams are investigated.
Keywords: GFRP,Wrapping Techniques.I INTRODUCTIONThe maintenance, rehabilitation and upgrading of structural members,is perhaps one of the most crucial problems in civil engineering applications.5 Moreover, a large number of structures constructed in the past using the olderdesign codes in different parts of the world are structurally unsafe accordingto the new design codes. Since replacement 3 of such deficient elements ofstructures incurs a huge amount of public money and time, strengthening hasbecome the acceptable way of improving their load carrying capacity andextending their service lives. Infrastructure 2 decay caused by prematuredeterioration of buildings and structures has led to the investigation ofseveral processes for repairing or strengthening purposes.
One of the challenges in strengthening of concrete structures isselection of a strengthening method that will enhance the strength andserviceability of the structure while addressing limitations such asconstructability, building operations, and budget. Structural strengthening maybe required due to many different situations. Additional strength may be needed to allow for higher loads to beplaced on the structure.
This is often required when the use of structurechanges and a higher load carrying capacity is needed. This can also occur ifadditional mechanical equipment, filing system, planters, or other items arebeing added to a structure.Strengthening may be neededto allow the structure to resist loads that were not anticipated in theoriginal design. This may be encountered when structural strengthening isrequired for loads resulting from wind and seismic forces or to improveresistance to blast loading.Additional strength may be needed due to a deficiency in thestructure’s ability to carry the original design loads. Deficiencies may be theresult of deterioration (Eg., Corrosion of steel reinforcement and loss ofconcrete section), structural damage (eg,. Vehicular impact, excessive wear,excessive loading and fire), or error in the original design or construction(eg.
, misplaced or missing reinforcing steel and inadequate concrete strength).Whendealing with such circumstances, each project has its own set of restrictionand demands. Whether addressing space restrictions, constructabilityrestrictions, durability demands, or any number of other issues, each projectrequires a great deal of creativity in arriving at a strengthening solution. II STRENGTHENING USING GFRP COMPOSITESOnly a few years ago, the construction market started to use FRP for structuralreinforcement, generally in combination with other construction materials suchas wood, steel, and concrete. FRPs exhibit several improved properties, such ashigh strength-weight ratio, high stiffness-weight ratio, flexibility in design,non-corrosiveness, high fatigue strength and ease of application. The use ofFRP sheets or plates bonded to concrete beams has been studied by severalresearchers. Strengthening with adhesive bonded fiber reinforced polymers hasbeen established as an effective method applicable to many types of concretestructures such as columns, beams, slabs, and walls. Because the FRP materialsare non- corrosive, non-magnetic, and resistant to various types of chemicals,they are increasingly being used for external reinforcement of existingconcrete structures.
From the past studies conducted it has been shown thatexternally bonded glass fiber-reinforced polymers (GFRP) can be used to enhancethe flexural, the flexible glass fiber sheets are found to be highly effectivefor strengthening of RC beams.III MATERIALSA.FiberSystem Thefiber system used in an FRP pultruded part can consist of different types andarchitectures of fiber materials. The raw fiber is processed and suppliedeither in strand form on a spool and known as roving or tow, or in broad goodsform on a roll and known as mat, fabric, veil, or tissue.
Two primary types of fiber systems are used when thehand-layup method is used for FRP strengthening: unidirectional tow sheets andunit-or multidirectional woven or stitched fabricssystem.B. FiberRoving Individualcontinuous fiber filaments are bundled, generally without a twist, intomultifilament strands known as roving that are used in the pultrusion processeither as is or in fabrics produced from roving. In the United States, rovingquantity is traditionally measured in units of yield (yd/lb). Roving isproduced in yields of 56, 62, 113, 225,250, 450, 495, 650, and 675.
Not allproducers manufacture all yields. The number of filaments in an individual rovingwith a specific yield depends on the fiber diameter of the filament. The mostcommon roving used in pultruded parts is a 113 yield roving, which hasapproximately 4000 filaments, usually having a diameter of 24 fm (93 X 10-3in.
) each. Figure 2.1 shows a spool of 113 yield glass fiber roving.C.Fiber Mats Continuous filament mat (CFM) also referred to in the United States ascontinuous strand mat, is the second most widely employed glass fiber productused in the pultrusion industry. CFM is used to provide crosswise (CW) ortransverse strength and stiffness in plate like parts or portions’ of parts(e.
g., the flange of a wide-flangeprofile) Fig. 1 woven glass roving combination fabricD.FiberglassFiberglass is a type of fiber reinforced plastic where thereinforcement fiber is specifically glass fiber. The glass fiber may berandomly arranged but is commonly woven into a mat. The plastic matrix may bea thermosetting plastic- most often epoxy.
Theglass fibers are made of various types of glass depending upon the fiberglassuse. These glasses all contain silica or silicate, with varying amounts ofoxides of calcium, magnesium, and sometimes boron. To be used in fiberglass,glass fibers are made with very low levels of defects.Fiberglass is a strong lightweightmaterial and is used for many products. Although it is not as strong and stiffas composites based on carbon fiber, it is less brittle and its raw materials aremuch cheaper. Its bulk strength andweight are also better than many metals, and it can be more readily molded intocomplex shapes.
Applications of fiberglass include aircraft, boats, automobiles,bath tubs and enclosures, hot tubs, septic tanks, water tanks, roofing, pipes,cladding, casts, surfboards, and external doorskins.IV EXPERIMENTALWORKA. ExperimentalworkTwo sets of beams were casted for this experimental test program. Inset of first three beams weak inflexure were casted using same grade of concrete and reinforcement detailing.In set of second three beams weak in shear were casted as same grade ofconcrete and reinforcement detailing. The dimensions of all the specimens areidentical. The cross sectional dimensions of both set of beams is 200mm by100mm and length is 1500mm. in SET first beams 2,8mm dia bar are provided asthe reinforcement and 6 mm dia bar as stirrups at the spacing of 150 mm C/C,set of second beams as identical and stirrups at the spacing of 250 mm C/C.
B. Casting of BeamsTwo sets of beams are identical. Reinforcement detail of beam andsection is shown in Fig 3.1& 3.2respectively.C.
Materials used for Casting1. Cement Ordinary Portland cement was used for the investigation. It was tested for its physical properties inaccordance with Indian Standard specifications.
Fig. 2 Reinforcement Details of beams Fig. 3 Section of beams2.
Fine aggregate The fine aggregate clear from allsorts of organic impurities was used in this experimental program. The fineaggregate was passing through 4.75mm sieve and had a specific gravity of 2.
65. Thegrading Zone of fine aggregate was Zone III as per IndianStandardspecifications.3.
CoarseaggregateThe coarse aggregates used were two grades available in local quarry.One grade contained aggregates passing through 4.75mm sieve and retained on10mm size sieve. Another grade contained aggregates passing through 10mm sizebut retained on 20mm sieve.4. WaterOrdinarytap water used for concrete mix in all mix.
5. FormWorkPly is used to prepare formworkfor beam of size 100mm x 200mm and 1500mm long. The form work is thoroughlycleaned and all the corners and junctions were properly sealed to avoid leakageof concrete through small openings. Shuttering oil was then applied to theinner face of the form work. The reinforcement cage is then placed in positioninside the form work carefully keeping in view a clear cover of 20 mm for thetop and bottom bars as shown in Fig 3.
3 Fig. 4 Casting of Beams V EXPERIMENTAL SETUPThe SET of I beams (F1,F2,F3,F4) are strengthening with flexural andSET II beams (S1,S2,S3,S4) are strengthening with shear. F1 and S1 are controlbeams. All the specimens were tested in the loading frame of concrete lab inBharath University. The testing procedure for the entire specimen was same.After the curing period of 28 days was over the beam as washed and its surfacewas cleaned for clear visibility of cracks.
The most commonly used loadarrangement for testing of beams will consist of two points loading. This hasthe advantages of substantial region of nearly uniform moment coupled with verysmall shears. The load will normally be concentrated at a suitable shorterdistance from a support.Two pointsloading can be conveniently provided by the arrangement shown in figure. Theload is transmitted through a load cell and spherical seating on a beam. Thisbeam bears on rollers scatted on steel plates bedded on the test member withmortar, high strength plaster or some similar material.The loading frame must be capable of carrying the expected test loadswithout significant distortion.
Ease of access to the middle third for crackobservations, deflection readings and possibly strain measurements as importantconsideration as is safety when failure occurs. The specimen was placed overthe two steel rollers bearing leaving ends of the beam. Two point loadingarrangement was done as shown in the figure 5. Two number of dial gauges wereused for recording the deflection of the beams. One dial gauge was placed justbelow the center of the beam and the remaining dial gauges were placed justbelow the point loads to measure deflections. After setting and reading all gauges the load was increased incrementally up tothe calculated working load, with loadsand deflections recorded at each stage, loads will then normally be increasedagain in similar increments upto failure, with deflection at this stage willusually be large and easily measured from a distance. Similarly cracking andmanual strain observations must be suspended as failure approaches unlessspecial safety are taken.
If it is essential that precise deflection readingsare taken upto collapse. Cracking and failure mode was checked visually and aload wasprepared.Fig.5 Experimental SetupVI DISCUSSIONS ONEXPERIMENTAL RESULTSA.General In this chapter, discussion is made on the effect of strengthening on thereinforced concrete beams by using different glass fiber with that of control beams, such as deflection and loadcarryingcapacity. Fig.6 wrapping techniques B. TestingProcedureBefore testing the member was checked dimensionallyand detail visual inspection made with all information carefully recorded.
After setting all, the load was increased up to the failure of beam anddeflection was recorded at each stage, and a load/deflection plot was prepared. C. FailureModeFailure modes have been observed in the experiments of RC beamsstrengthened by GFRP. The GFRP strengthened beams and the control beams aretested to find out their ultimate load carrying capacity. The SET of I beams(F1,F2,F3,F4) are strengthening with flexural and SET II beams (S1,S2,S3,S4)are strengthening with shear. F1 and S1 are control beams.
After setting andreading all gauges the load was increased incrementally up to the calculatedworking load, with loads and deflections recorded at each stage. A number offailure modes have been observed in the experiments of RC beams strengthened inflexure and shear by GFRPs. These include flexure failure, shear failure due toGFRP rupture and crushing of concrete at the top. Cover delamination or FRP bonding can occur if the force in theFRP cannot be sustained. The GFRP strengthened beam and the control beams weretested to find out their ultimate load carrying capacity. It was found that thecontrol beams were failed. In set ofthree beams are failure in flexure and other set of three beams are failureinshear.D.
With Respect to Load and Deflection From the load of deflection of data of SET I beamsF1, F2, F3 and F4, load vs deflection is plotted for all the four beams. Fromthis load Vs deflection curve it is clear that beam F1 has lower ultimate load carrying capacity compared to beamsF2, F3 andF4. Bottom side wrapping Graph 1 Load Vs Deflection Curve for beam F1,F2, F3& F4Deflection of beam for bottomside GFRP wrap. 1.
The beam with bottom side single mat wrap is having the more deflectionthan that of double mat wrap and woven rovingwrap.2. The beam with bottom side double mat wrap is having the minimumdeflection than that of single matwrap.3. Similarly, the beam with bottom side woven roving wrap is having theminimum deflection than that of single mat wrap and double mat wrap. E. Both sides wrappingFrom the load of deflection of data of SET II beams S1, S2, S3 and S4,load vs deflection is plotted for all the four beams. From this load Vsdeflection curve it is clear that beam S1 has lower ultimate load carrying capacity compared to beams S2, S3 andS4.
Graph 2 Load Vs Deflection Curve for beam S1,S2,S3& S4Deflection of beam for both sideGFRP wrap.1. The beam with both sidesingle mat wrap is having the more deflection than that of double mat wrap andwoven rovingwrap.2.
The beam with both sidedouble mat wrap is having the minimum deflection than that of single matwrap. 1. Load at Initial Crack Load at Initial Crack of SET I Beams Graph 3 Load at Initial Crack of SET I Beams Two pointloading was done on both SETI and SETII beams and at the each load anddeflection and crack development were observed. The load at intial crack of allbeams was observed, recorded and is shown in graph 3 and 4. Loadat Initial Crack of SET II Beams Graph.
4 Loadsat Initial Crack of SET II Beams 2. Ultimate Load Carrying CapacityThe load carrying capacity of thecontrols beams and the strengthen beams were found out. The control beams wereloaded up to their ultimate load. The strengthen beams F2, F3,F4 and S2,S3,S4are had the higher load carrying capacity compared to the controlled beam F1and S1. An important character to be noticed about the usage of GFRP sheets ishigh ductile behavior of the beams. Graph 5 Ultimate Load of SET I BeamsThe shearfailure being sudden can lead to huge can give us damage to the structure. But the Behavior obtained by the use of GFRP can give us enough warning before thefailure.
Graph 6.6Ultimate Load of SET II Beams VII CONCLUSIONSIn this experimental investigation the flexural and shear behavior ofreinforced concrete beam strengthened by GFRP sheets are studied. Two sets ofreinforced concrete beams, inset I four beams one is control beam and otherthree are weak in flexural and SET II beams one is control beam and other threewere in weak in shear were casted and tested. From the test results andcalculated strength values the following conclusions are drawn.SET Beams(F1, F2, F3 andF4)1) Initial flexural cracksappear at a load by strengthening thebeam.
The ultimate load carrying capacity of the strengthen beam F2 is 7% morethan the controlled beamF1.2) Load at initial cracks isfurther increased by strengthening ofbeam .the ultimate load carrying capacity of strengthen beam F3 is 7% more thanthe controlled beamF1.
3) Load at initial cracks isfurther increased by strengthening ofbeam .the ultimate load carrying capacity of strengthen beam F4 is 24% morethan the controlled beamF1.4) When the beam is not strengthen it failed in flexure but after strengthening the beam is flexural, theflexural failure of the beam as it does not give much warning before failure. Therefore it is recommended to check theshear strength of the beam and carry out shear strengthening along withflexural strengthening if required.5) Flexural strengthening up to the neutral axis of the beam increase the ultimate loadcarrying capacity but the cracksdeveloped.
6) By strengthening up to the neutral axis of the beam increase in theultimate load carrying capacity of the beam and cost involvement is almostthree times compared to the beamstrengthen byGFRP. SET II Beams (S1, S2, S3andS4)1) The control beam S1 failed in shear it was made weak inshear.2) The initial crack in the strengthen beams S2 and S3 appears at higherload compared to the control beamS1.3) After strengthening the shear zone of the beam the initial cracksappears at the flexural zone of the beams and the crack is widen. The finalfailure is shear in the beam and theultimate load capacity of the beam S2 is13% more than the controlled beamS1.
4) When the beam is both sides wrapping in the shear zone the ultimateload carrying capacity of allbeams.5) The beam S3 having the 13% ultimate load carryingcapacity.6) The bonding between GFRP sheets and the concrete is in act up to thefailure of the beam which clearly indicates the composite action due toGFRPsheet.
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