8

CHAPTER 2

LITERATURE REVIEW

2.1 GENERAL

Fibre reinforced plastic (FRP) reinforcement plays a very

important role in the retrofitting and rehabilitation of reinforced concrete

(RC) structural elements as an external reinforcements. Recent

developments in these fields are widespread. Several investigators carried out

experimental and/ or theoretical investigations on concrete beams and

columns retrofitted with carbon/glass fibre reinforced polymer (CFRP, GFRP,

and HYBRID) composites in order to study their effectiveness. Many

practical applications worldwide now confirm that the technique of bonding

FRP laminates or plates to external surfaces is a technically sound and

practically efficient method of strengthening and upgrading of reinforced

concrete load-bearing members that are structurally inadequate, damaged or

deteriorated. Of all the materials used as external plate reinforcement, carbon

fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP)

composite materials have found special favour with engineers and applicators

because of their many advantages. After that over a period of time some

researchers started doing their work on Hybrid FRP (combined layer of CFRP

and GFRP fibres).

2.2 STATE OF ART OF THE WORK

Some of the significant research works carried out several

researchers on RCC beams and columns for the past several decades using

CFRP, GFRP, and Hybrid FRP are discussed below.

9

2.2.1 Carbon Fibre Reinforced Polymer Wrapping on RCC beam

Alessandra Aprile et al (2001), found that RCC beams strengthened

by steel plates showed a ductile response, mainly due to yielding of the

strengthening plate. The RCC beams strengthened by CFRP plates showed a

brittle response, as the response was dominated by the elastic behaviour of the

plate.

Omar Ahmed et al (2001), has proposed design formulae to predict

the strength of Carbon-Fibre-Reinforced Plastic (CFRP) strengthened beams,

particularly when premature failure through laminates-end shear or concrete

cover delamination occurs. The technique of externally bonded CFRP

laminates achieved considerable strengthening efficiency, particularly in case

of smaller un-sheeted length and adequate strengthening ratios. The

predictions using the proposed formulae were compared with the

experimental results, as well as with the calculated design limit states.

Francesco Bencardino et al (2002), conducted an experimental

investigation of reinforced concrete beams strengthened in flexure and shear

using externally epoxy bonded bidirectional carbon fibre fabric to overcome

the bond slip and plate separation at the ends. In conclusion that the results

reported herein show that CF fabrics can provide an effective and efficient

alternative to laminates strengthening existing concrete structures.

Rania AI-Ham et al (2006) investigated on flexural behaviour of

corroded steel reinforced concrete beams under repeated loading. This

investigation was carried out on thirty beams of sizes 152x254x2000mm

repaired with carbon fibre reinforced polymer (CFRP) sheets. The authors

reported that repairing with CFRP sheets increased the fatigue capacity of the

beams with corroded steel reinforcement beyond that of the control

unrepaired beams with un-corroded steel reinforcement. Beams repaired with

10

CFRP at a medium corrosion level and then further corroded to a high

corrosion level before testing had a comparable fatigue performance to those

that were repaired and tested after corroding directly to a high corrosion level.

Christopher (2006) established that several common beliefs related

to deboning failure in FRP strengthened concrete beams are not correct.

Specifically, for plate end de-bonding, a physically sound failure criterion

should not be based on elastic stresses. When de-bonding initiates form a

crack at the middle of the beam, the drastic decrease of de-bonding stress with

plate thickness, predicted by existing models, is not found in real specimens.

Abdelhak Bousselham and Omar Chaallal (2006), made an

experimental investigation on the behaviour of reinforced concrete T-beams

retrofitted in shear with externally bonded CFRP composite. The authors

concluded that the shear capacity gain due to the CFRP was greater for deep

specimens than for slender specimens.

Carlos and Maria (2006), conducted an experiment and found

numerical results validated against experimental data obtained from 19 beams

strengthened with different types of FRP. They derived the numerical

simulations and which indicates that the concrete tensile strength does not

constitute the unique failure criterion for predicting plate debonding failure of

strengthened RC beams.

Hedong Niu and Zhishen Wu (2006), analysed the effect of

interface bond properties on the performance of FRP-strengthened reinforced

concrete (RC) beams in terms of concrete cracking, interface stress transfer,

and failure mechanisms using nonlinear fracture mechanics based finite

element analyses. They concluded that, low stiffness may be helpful to

distribute more uniform stresses in both steel and FRP sheets, which may help

11

to relieve local stress concentrations and reduce the likelihood of debonding

in practice.

Tamer EI Maaddawy et al (2007) presented results of an

experimental study designed to evaluate the performance of reinforced

concrete beams repaired with carbon fibre reinforced polymer (CFRP) Sheets

under corrosive environmental conditions. The authors concluded that the

deflection capacity of the beams decreased as corrosion progressed after

repair. The deflection capacity of the repaired beams was on an average

approximately 45% lower than that of the control beam.

Joseph Robert Yost et al (2007) conducted an investigation on

twelve full scale concrete beams strengthened with NSM (Near-Surface-

Mounted) carbon FRP (CFRP) strips to examine the parameters of steel and

FRP reinforcement ratios. They concluded that, there was a measurable

increase in yield and ultimate strengths; predictable nominal strengths and

failure modes; and effective force transfer between the CFRP, epoxy grout,

and surrounding concrete, also, strengthening with CFRP resulted in a

decrease in both energy ductility and defection ductility.

Barros et al (2007) investigated experimentally the efficacies of the

near surface mounted (NSM) and externally bonded reinforcing (EBR)

techniques for the flexural and shear strengthening of reinforced concrete

(RC) beams. They concluded that the CFRP shear strengthening systems

applied in their work increased significantly the shear resistance of concrete

beam. For the flexural strengthening, the NSM technique was the most

effective, but the difference between the efficiency of NSM and EBR

techniques decreased with the increase of the longitudinal equivalent

reinforcement ratio.

12

Byong (2008) highlighted the effect of using epoxy mortar patch

end anchorages on the flexural behaviour of reinforced concrete beams

strengthened with carbon Fibre-reinforced polymer (CFRP) sheets. The test

results show that the premature debonding failure in RC beams strengthened

with CFRP sheets can be delayed or prevented by using epoxy mortar patch

end anchorages, thereby enhancing flexural performance. They proved that

the mortar patch anchorage used in their experimental study was very

effective in delaying or preventing the premature debonding failure, that is the

dominant failure mode for beams conventionally strengthened with CFRP.

Mahmut Ekenel and John (2009) proved that, fatigue resistance of

RC beams is improved by strengthening with CFRP fabrics. The increase in

stiffness of the CFRP control beam was approximately two times that of the

un strengthened beam. All CFRP-strengthened beams survived fatigue testing

of 2 million cycles. Delaminations significantly decreased the stiffness of the

CFRP-strengthened beams, the average decrease being 15% relative to

specimens without defects.

Sarah Orton and James (2009) conducted an experiment to study

the Strengthening of the negative moment region and were able to reach the

required load to resist progressive collapse by forcing hinging to occur at

locations of greater rotational ductility and were able to use far less CFRP

material. The flexural strengthening scheme was able to achieve the required

load to resist progressive collapse at a low level of displacement, but required

a much greater amount of CFRP. It was found that a strategy to provide

continuity of reinforcement in a concrete beam using CFRP can be successful

but may or may not be sufficient to limit progressive collapse.

Balamuralikrishnan et al (2009) conducted an experimental study

on beams to evaluate the performance of RCC beams bonded with single and

double layer CFRP fabric at the soffit of the beam under static and cyclic

13

loading. The authors concluded that CFRP fabric properly bonded to the

tension face of RC beams can enhance the flexural strength substantially. The

strengthened beams exhibit an increase in flexural strength of 18 to 20 percent

for single layer and 40 to45 percent for two layers both static and

compression cyclic loading respectively. Minimum two layers of CFRP fabric

should be bonded to get the desired results. The strengthened beams with one

layer and two layers, exhibit 20 % and 45% increase in flexural strength when

compared to the control specimen.

Yasmeen Taleb Obaidat (2010) investigated the behaviour of

structurally damaged full-scale reinforced concrete beams retrofitted with

CFRP laminates in shear or in flexure experimentally. The main variables

considered by them were the internal reinforcement ratio, position of

retrofitting and the length of CFRP. The experimental results indicates that

beams retrofitted in shear and flexure by using CFRP laminates are

structurally efficient and are restored to stiffness and strength values nearly

equal to or greater than these of the control beams. They found that the

efficiency of the strengthening technique by CFRP in flexure varied

depending of the length. The main failure mode in the experimental work was

plate debonding in retrofitted beams.

Balasubramanian et al (2010) presented an experiment on Beam

Column joint to study the effect of spacing of stirrups and effectiveness of

CFRP wraps in increasing the load caring capacity. He concluded that, there

was only a marginal increase in the load capacity of the RC beam-column

joint specimens, as the stirrup spacing is decreased from 200 mm to 100 mm

and reduction in the joint capacity as the axial load is increased from 15% to

45% on the columns in the case of the stirrup spacing of 200mm.The beam

column joint specimens with stirrup spacing as per IS 456:2000 failed in the

joint portion with extensive cracking and spalling of concrete in the joint

14

region. The CFRP wrapping of the beam column joint specimens enhanced

the load carrying capacity of the joint by 25-30% over the stirrups spacing

200 and 15-25% over stirrups spacing 100 series for the three axial loads

investigated. The enhancement in the energy absorption capacity of the

wrapped specimens was in the range 28-39% over stirrups spacing 200 series

and 19-34% over stirrups spacing 100.The repaired and wrapped specimens

showed an increase of nearly 66-72% in the load capacity over the control

stirrups spacing 200 specimens.

Nadeem et al (2010) presented the results of experimental study

made on beams wrapped with CFRP and their test results clearly indicated

that flexural strength can be substantially improved by externally bonding the

CFRP sheets to the tension face of under-reinforced RC Beams. However, the

percentage increase is dependent of steel reinforcement ratio. There is no

universally accepted definition of structural ductility. In order to develop a

rational and meaningful concept of ductility that may be applied to all

structural materials, a reference base is required. The yield point of internal

steel provides a very objective reference point to define ductility. However, it

is the unique yield plateau of the stress-strain curve of steel which impart the

structural member an ability to sustain load while undergoing large

deformations. This is not that case when the reinforcing medium is fibre

reinforced polymer (FRP), or a mixture of steel and FRP, as in the case of

FRP sheet bonded RC beams, following expression was used to calculate the

ductility index of control and CFRP strengthened beams:

Mid-span deflection at peak loadDuctility index =

Mid-span deflection at tension steel yield .. (2.1)

Shihy et al (2010) reported that, strengthening of composite beams

and concrete slab strengthened with CFRP sheets increased the load carrying

15

capacity of the beam by 15%. This increase is related to the thickness of the

CFRP sheet; doubling the sheet thickness increased the ultimate capacity of

the beams to 21%.The load carrying capacity of the flexure strengthened

beams with corrugated sheet predicted by the experimental data is higher than

that of the control beams by 12%. The ductility of strengthened beams has a

range of 2.4 to 2.5 compared to 3.5 for the control beam. The low ductility of

strengthened beam indicates that addition of CFRP as reinforcement greatly

reduces the deforming ability at the ultimate stage of loading.

Murat Tanarslan et al (2010) concluded that the CFRP composites

have no ductility as a material and this could lead to undesirable brittle failure

in the strengthened elements. Specimens were also heavily damaged.

However, ductility of 1.04 to 1.99 was obtained from the repaired and

strengthened specimens. It was not possible to state that the CFRP

strengthened RC beams behaved in a ductile way, but the result achieved

were still attractive.

Ysmeen Taleb Obaidat et al (2011) presented the results of the

experimental study conducted to investigate the behaviour of structurally

damaged full-scale reinforced concrete beams retrofitted with CFRP

laminates in shear or in flexure. The main variables considered were the

internal reinforcement ratio, position of retrofitting and the length of CFRP.

The stiffness of the CFRP-retrofitted beams had increased compared to that of

the control beams. Employing externally bonded CFRP plates resulted in an

increase in maximum load. The increase in maximum load of the retrofitted

specimens reached values of about 23% for retrofitting in shear and between

7% and 33% for retrofitting in flexure. More over retrofitting shifts the mode

of failure to be brittle. The results showed that the main failure mode was

plate debonding which reduced the efficiency of retrofitting.

16

Karim Benzarti et al (2011) studied the durability of the adhesive

bond between concrete and carbon fibre reinforced polymers (CFRP)

strengthening systems has been investigated under accelerated ageing

conditions. Humid ageing causes a progressive and significant decrease in the

pull-off strength of the bonded interfaces for CFS and CFRP strengthened

specimens prepared form non carbonated concrete slabs. Epoxy adhesives

used for the bonding exhibited a decrease in mechanical strength during

humid ageing, as well as pronounced elasto-plastic behaviour.

Itaru NIshizakia et al (2011) conducted an experiment to investigate

the durability of the bond between carbon fibre sheet reinforcement and

concrete. They concluded that the pull-off adhesive strength slightly

decreased after 14 years of exposure, but the residual values still indicated

quite good adhesive properties. Further they proved that, the slight decrease in

pull- off strength dose not necessarily indicate a change in the properties of

the bond between Carbon fibre sheet and concrete. As regards specimens

immersed in water, pull- off results was in few cases consistent with the peel

characterizations, showing significant evolutions in the strength and failure

mode. For most specimens, the two methods provided divergent trends. In the

end, this study suggested that the peel test could be relevant for evaluating the

durability of the bond between CF sheet and concrete, while the

representativeness of the pull-off test remains a matter of discussion.

Maia Antonietta Aiello and Luciano Ombres (2011) presented

experimental and theoretical studies on the structural behaviour of RC

continues beams strengthened with CFRP laminates and concluded that

adequate strengthening configurations allow the obtainment of significant

percentages of moment redistribution. For analyzed beams, the percentage of

moment redistribution reaches 20%. A modified ductility index has been

introduced to take the softening behaviour of the strengthened beams into

17

account. The obtained values of this index show that beams can also be

attained by an adequate reinforcement configuration; The performed analysis

shows that the redistribution phenomenon occurs at different loading levels

not only at the ultimate load, because of the influence of the cracking

evolution. That occurrence could be taken into account at the design stage be

defining appropriate permissible limits of redistribution.

Rania AI-Hammoud et al (2011) investigated the flexural

behaviour of thirty numbers of (152x254x2000mm) corroded steel

reinforcement beams repaired with CFRP sheets under repeated loading. They

concluded that, repairing with a double flexural CFRP sheet at a high

corrosion level increased the flexural fatigue capacity of corroded beams by

42% at 50000 cycles and 17% at 750000 cycles compared to the corroded

beams. Further the found that there was no difference in strength between

repairing the beams with a single layer and a double layer of CFRP sheets.

When severely cracked beams were repaired with FRP, their life was

extended by about 10 times, suggesting that beams in service could be

effectively rehabilitated using FRP. High-modulus FRP sheets have excellent

tensile and fatigue strength properties but little global ductility.

Ferrier et al (2011) developed a model for evaluation of the beams

mechanical properties under fatigue loading. The result showed that with a

suitable anchorage length and fatigue loads applied on the strengthened beams

the composite improves the fatigue behaviour of RC beams. With a load

corresponding to 84% of the carrying capacity of a RC beam, the fatigue

behaviour of the beam is improved. Further the results for the larger beams

show that the overall behaviour of RC beams is improved with the use of

external FRP strengthening: a better fatigue behaviour is obtained, with a 40%

increase in the service load.

18

Noel and Gardner (2011), Compared codel provision regard to

span/thickness limits of ACI 318-08, CSA 23.3-04, BS 8110-97, AS 3600-

2009, Euro code 2(2004), ACI Committee 435 revisions and the author

concludes that incremental deflection after construction of partitions and

finishes is more critical than immediate deflection. There is also general

agreement that the limiting incremental deflections are span /500 for brittle

partitions, otherwise, span /250. For purpose of calculating the incremental

deflections, they have given a suggestion that the service load be calculated

from the equation, Service load= D + L, where 0.4 for offices, apartments,

etc., and 0.8 for storage, which is a compromise between the provision of BS

8110-97 and AS 3600-2009.

Halil Sezen et al (2011) conducted an experimental evaluation of

axial behaviour of strengthened circular RC Columns and they concluded

that, concrete jacketing with WWF reinforcement and FRP Wraps increased

the axial strength of the un retrofitted or base column by up to 140%, but both

methods resulted in brittle failure immediately after the maximum axial

capacity was reached. Since FRP dose not increase the original column size,

the axial strength increase is primarily attributable to additional confinement

provided for the existing concrete. FRP composite strips were less effective

and ruptured earlier than the full length FRP Wraps.

2.2.2 Glass Fibre Reinforced Polymer Wrapping on RCC Beam

Balasubramanaian et al (2007), evaluated the performance of the

CFRP/GFRP wraps used for retrofitting of the beams and columns and

concluded that, the performance of the RC beams was found to have

improved after retrofitting using FRP wrapping. But the performance of both

CFRP and GFRP were almost similar. In case of the shear strengthening, the

RC beams provided with CFRP wrap along the entire span was found to be

better among the various methods of carbon fibre wrap that were investigated.

19

For RC columns retrofitted with single layer of CFRP/GFRP wrap, peak load,

maximum strains as well as ductility index were higher than the control RC

columns for both the lateral tie spacing.

Sing-ping Chiew et al (2007), presented an experimental and

numerical study for flexural behaviour of RCC beams strengthened with

GFRP and concluded that by bonding GFRP laminates to the tension face of

flexural RC beams; both strength and stiffness of the beams can be increased.

The strengthening ratio increases linearly with the increase of the axial

rigidity of the external GFRP laminates. The interfacial shear stress

concentration due to the cut off effect is less significant than that caused by

flexural cracking. Debonding failure occur when the interfacial bond in the

shear span is fully utilized. All the strengthened beams fail by de-bonding of

GFRP laminates.

Pannirselvam et al (2008), presented a General Regression Neural

network(GRNN) based computational model for Predicting the yield load,

ultimate load, yield deflection, ultimate deflection, deflection ductility and

energy ductility of such beams. The results showed that strength of GFRP

plated beams was higher than corresponding unplated beams. The yield

strength increased by a maximum of 76.49% and 11.78% for 3mm thick and

5mm thick CFRP plating respectively. The maximum deflection levels

achieved by the FFRP plated beams were to 10.71% and 34.67% higher for

3mm and 5 mm thick GFRP plating, when compared to the unplated reference

beams. The ductility values of plated beams increased by a maximum of

38.61 and 141.63% for 3 and 5mm thick GFRP plating respectively.

Tan et al (2009) carryout an analytical and experimental

investigation on glass FRP-strengthened RC beams under the combined effect

of sustained loading and tropical weathering. They concluded that FRP-

strengthened RC beams under sustained loads exhibited larger deflections and

20

crack widths, when subjected to tropical weathering at the same time. They

showed smaller deflections and crack widths when strengthened with a higher

FRP reinforcement ratio. Both the strength and ductility of beams under

sustained loads decreased with the longer weathering periods.

Kim et al (2010) presented a design orientated conclusions are

deduced from the experimental, analytical and parametric studies. Anchors in

GFRP-reinforced GFRC behave and exhibit a pull-out mode of failure as

expected form steel or FRP-reinforced plain concrete. The pull-out resistance

in GFRP is slightly greater in GFRC than in plain concrete. The flexural

capacity and deformations of GFRP-reinforced GFRC elements can be

predicted by FEA provided the tensile properties of the GFRC are determined

and modelled correctly.

Jadhav and Shiyekar (2011) carried out experimental studies, to

investigate the effect of length, width and number of layers of glass fibre

reinforced polymer (GFRP) strips applied to the tension side of the RC Beam.

The authors concluded that, the beam strengthened with different width and

number of layers of glass fibre reinforced polymer (GFRP) strips exhibited

relatively good ductile behaviour. However it showed same load at yielding of

steel. This was because the glass fibre reinforced polymer had higher initial

stiffness. Hence, it contributed to strengthening more effectively. The load

carrying of the strengthened beams increased by 7% to 35% when compared

to the control beam.

2.2.3 Hybrid Fibre Reinforced Polymer Wrapping on RCC Beam

Maria Antonietta Aiello et al (2002) analyses to study the structural

behaviour of concrete beams reinforced with hybrid fibre-reinforced polymer

(FRP)-steel reinforcements. They observed from the experiment that the

increase of stiffness is more evident for beams reinforced with FRP rebars

21

placed near the outer surface of the tensile zone and steel rebars placed at the

inner level of the tensile zone.

Abdelhady Hosny et al (2006), made an elaborate study on the

behaviour of RC beams strengthened with hybrid fibre reinforced polymer

(HFRP) laminates. They observed that use of CFRP and GFRP laminates for

strengthening RC T-beam is an effective method to increase its ultimate load

carrying capacity and using a combination of CFRP and GFRP laminates is an

effective method to enhance the ductility of the strengthened beams.

Robert Ravi and Prince Arulraj (2010) reported the Experimental

investigations carried out on the control and retrofitted Beam- column joint

specimens using GFRP- CFRP /CFRP-GFRP Hybrid wrapping. They

concluded that the load carrying capacity of the reinforced concrete beam-

column joint specimen retrofitted with GFRP-CFRP sheet was found to be

19.5% and 25% for specimen retrofitted with CFRP-GFRP sheet than the

control specimens. The energy absorption capacity of the reinforced concrete

beam –column joint specimen retrofitted with GFRP-CFRP Sheet was found

to be 24.2% and that of specimen retrofitted with CFRP-GFRP Sheet was

31.1% than control specimens.

Khaled Galal and Amir Mofidi (2009) examined the effectiveness

of a new FRP sheet/ductile anchor system for increasing the flexural capacity

and ductility of RC beams. They mainly concluded that the presence of

Hybrid FRP / ductile anchorage in the externally bonded CFRP system

prevented early peel off of the CFRP sheet, which enhanced the T-beam

strength and ductility. The ultimate load of the T- beam strengthened with

externally bonded CFRP along with hybrid FRP/ ductile anchorage was about

27% higher than that the control T-beam, whereas the midspan deflection at

ultimate load was 19 % lower than that of the control.

22

Dond-Uk Choi et al (2011) conducted a analytical and experimental

study consists of material, structural, and bond tests, as well as the evaluation

of the ACI 440 and ISIS documents and concluded that, the volumetric ratio

between GF and CF needs to be (6.8/1) or greater to promote pseudo-ductile

behaviour. The beams were strengthened using hybrid FRP sheets with

carbon-to-glass ratio of (8.8/1) and exhibited higher peak loads than the un

strengthened beams by approximately 20%, sustained peak loads without

degradation after the peak, and demonstrated pseudo-ductile behaviour. The

maximum absolute amount of hybrid sheets to ensure ductile behaviour of RC

beam needs to be considered. The specimen with two plies of the hybrid

sheets (HF-2ply) had a hybrid FRP amount of approximately 75% of the

maximum. The effective bond length of the tested hybrid FRP sheet was

approximately 8 in. (200 mm), and the bond shear stress capacity between the

hybrid FRP sheet and concrete was on the order of 3 MPa (430 psi),

Comparable to that between the carbon FRP sheet and concrete.

Ferrier et al (2011) examined the damage behaviour of FRP-

strengthened reinforced concrete (RC) Structures subjected to fatigue loading.

Based on the research, two design force-strain relationships were proposed for

hybrid carbon-glass FRP sheets, with and without consideration of hybrid

effects. The specimen with two plies of the hybrid sheets (HF-2ply) had a

hybrid FRP amount of approximately 75% of the maximum. The effective

bond length of the tested hybrid FRP sheet was approximately 8 in. (200

mm), and the bond shear stress capacity between the hybrid FRP sheet and

concrete was on the order of 3 MPa (430 psi), Comparable to that between the

carbon FRP sheet and concrete.

Zakari Hossain et al (2011) evaluated the flexural behaviour and

the effectiveness of carbon fibre in thin Cement Composites. They found that,

the addition of small amount of Carbon fibre not only increased the bearing

23

Capacity of cement Composites but also significantly improved the Ductility

and Young’s moduli of Mortar matrix. It has been demonstrated that the

Maximum load was recorded at the deflection of nearly 0.5mm (0.019 in)-

0.7mm (0.027 in) and the Post-Crack load Deflection Performances of

Cement Composite were enhanced by mixing the Varying Lengths of fibre.

Among the three Categories of Fibre Tested in this Study, the dimensional

hybrids of carbon Fibre appeared to be more effective than the individual

ones.

2.2.4 Carbon Fibre Reinforced Polymer Wrapping on RCC Column

Luke et al (2005) presented an experimental study of full –scale fire

endurance tests on circular FRP wrapped and insulated reinforced concrete

columns and they concluded that insulation system described herein is an

effective protection system to maintain the overall load –carrying capacity of

FRP- wrapped reinforced concrete columns during fire. The insulation

remained intact for more than 5 hours of exposure to the ASTME 119 fire. It

is possible, with the requisite thickness of the insulation to maintain the

temperature of FRP wrap below 100 C to 4 hours during exposure to the

standard fire.

Mohamed El Gawady et al (2006), conducted an experiment to

asses the cyclic performance of RC column using CFRP jackets and

concluded that CFRP and steel jacketing altered the model of Failure from lap

splice failure and /or flexural failure to low-cycle fatigue rupture of the

longitudinal bars. Damage in all the retrofitted specimens was concentrated in

the gap between the jacket and the column base. The retrofitted columns were

able to sustain their lateral strength to displace ductility levels that were 1.1 to

1.4 times the ductility levels attained by the as-built specimens.

24

Wilkins Aquino and Neil (2007), evaluated the feasibility of using

carbon composites to restore the seismic effectiveness of corrosion-damaged

reinforced concrete bridge columns with inadequate length lap-spliced

reinforcement at their base and subjected to severe environmental conditions.

Columns retrofitted with carbon composites, and having well consolidated

repair concrete had maximum load and ductility capacities exceeding those of

a control column, which simulated the original as-built condition.

Kumar et al (2007) established that retrofitting of previously

damaged columns with CFRP jackets resulted in improvements in strength

and ductility. The level of improvement, however, would be dependent on the

damage experienced by the column prior to retrofitting. High axial load

resulted inconsiderable reduction in the ductility and energy dissipation

capacity of the columns, with the work index indicative of energy dissipation

capacity being the worst affected parameter; and ductility improvement in

square columns with lap splices as a result of CFRP retrofitting were

significantly lower than that for comparable circular columns due to more

efficient confinement mechanism in circular shapes. The CFRP retrofitting

technique was found to be effective in enhancing the seismic resistance of the

columns and resulted in more stable hysteresis cures with lower stiffness and

strength degradations as compared with the un retrofitted columns.

Wikins Aqino et al (2007) established that advanced composite

materials (ACMs) are a viable alternative for the repair and seismic upgrading

of corroded columns. Columns retrofitted properly with carbon composite

(CFRP) wraps had load and ductility capacities matching or exceeding those

expected for an undamaged seismically designed column. Load and ductility

capacities exceeded those of an undamaged control specimen with an

inadequate length lap splice at the column to foundation beam connection.

25

The use of external currents is feasible for inducing corrosion in large-scale

laboratory tests.

Alper llki et al (2008) presented an experimental study on CFRP

jacketed low and medium strength circular, square, and rectangular reinforced

concrete columns with or without sufficient transverse reinforcement, and

concluded that CFRP Jackets increased the compressive strength and

corresponding axial strain of the column with circular, square, and rectangular

cross sections. While the strength enhancement was more pronounced for

circular cross sections, deformability enhancement was more for square and

rectangular cross section both for the cases of low and medium strength

concrete. CFRP jackets prevented buckling of longitudinal bars and

maintained the dual confinement effect provided together with internal

transverse bars, as well as preventing spalling of cover concrete.

Mohsen et al (2009) conducted an experiment on 55 numbers of

150mm diameter with varying height circular reinforced concrete column

tested under axial loading. The authors concluded that externally bonded

CFRP sheets were very effective in enhancing the axial strength and

deformation Capacity of concrete Column. The failure mode of the confined

RC columns was sudden in the form of CFRP sheet fracture at the mid height

of the specimen followed by the fracturing of the lateral reinforcement and

buckling of the longitudinal reinforcement. In the unconfined columns, the

failure mode was also sudden due to the column failure of the lateral

reinforcement and the outer concrete by buckling of the longitudinal

reinforcement. The influence of the number of CFRP layer on the ductility,

confinement effectives, and ultimate load improvement percentage is

significant.The concept of ductility is related to the ability of a structural

member to sustain inelastic deflection without substantial decrease in the load

carrying capacity. In RC column the ductility was an important issue due to

26

their brittle failure mode increase in ductility is directly related to the increase

in the number of layers of CFRP sheets

Mathai et al (2010) presented an experimental and analytical

investigation conducted to assess the behaviour of beam –column wrapped

with GFRP. One specimen without GFRP wrapping and three specimens with

2,4 and 6 layers of GFRP wrapping. The authors found that, the Specimen

jacketed with 6 Layers of GFRP had the highest load carrying capacity of

38% and increased ductility of 68% compared with the specimen without

GFRP wrapping. Ductility is the property which allows the structures to

undergo large deflection without loosing its strength. Ductility is quantified

by ductility factor, which is the ratio of displacement at failure stage to the

displacement at yield point. At higher levels of lateral displacement, the

energy absorbed by the beam –column wrapped with GFRP was much higher

than the beam-column without GFRP wrapping

Mare Quiertant and Jean- Luc Clement (2011) established that,

depending on the CFRP Strengthening system (type of material and bonding

process), significant increase in deformability and strength can be achieved

for column under combined flexural compressive loading. The maximum

strength enhancement was characterized by a ratio of 1.30. Deformation

capacity and ductility improvement was more distinctive than the gains in

strength.

Varma and Jangid (2011), investigated the residual strength

properties of FRP strengthened concrete cylinders, when subjected to elevated

temperatures and they concluded that, the external strengthening of concrete

structures, particularly columns, and provides much enhanced load carrying

capacity to the extent of about 94% compared to the bare columns. FRP loses

its entire confining strength at about 400o C and needs insulation. The FRP is

27

a fairly good heat insulator and multiple layers will be effective even at higher

temperature

Yaqub (2011), experimentally investigated the post repair

compressive performance of post- heated reinforced concrete square columns

warred with a single layer of unidirectional GFRP or CFRP tested under axial

Compression. The sudden and explosive nature of the failure indicates the

release of a significant amount of energy as a result of the uniform confining

stress provided by the fibre jacket due to rounding of the square corners.

Indicating a more brittle failure in the carbon fibre reinforced polymer. It can

be seen from fig that the values of axial strains at the ultimate loads were

significantly lower in the unheated columns Compared to the post heated

columns. The failure of GFRP or CFRP wrapped post heated columns took

Ductility of columns. This could be attributed to the fibre reinforced Polymer

laminate providing confinement to the micro cracked post- heated concrete

resulting in an increase in the columns load carrying capacity with a higher

value of axial strain and lateral strain. GFRP and CFRP jackets provide

effective confinement near ultimate conditions and could be used to enhance

the strength and ductility of fire damaged reinforced concrete square columns.

2.2.5 Glass Fibre Reinforced Polymer Wrapping on RCC Column

Muhammad and Shamim (2005) evaluated the effectiveness of

glass Fibre reinforced polymer (GFRP) wraps in strengthening deficient and

repairing damaged square concrete columns. Concluded square concrete

columns externally retrofitted by GFRP wraps and tested under axial

compression and cyclic loading, simulating seismic loads, showed

pronounced un retrofitted columns. Higher ductility and improved seismic

performance can be achieved by retrofitting damaged square concrete

columns with GFRP jackets.

28

Kumutha et al (2007) conducted an experiment to evaluate the

effectiveness of external GFRP strengthening for rectangular concrete

columns to evaluate the effect of number of GFRP layers on the ultimate load

and ductility of confined concrete. Effective confinement with GFRP

composite sheets resulted in improving the compressive strength. better

confinement was achieved when the number of layers of GFRP wrap was

increased, resulting in enhanced load carrying capacity of the column, in

addition to the improvement of the ductility.

Gian Piero Lignola et al (2007) reported a study on seven hollow

square cross section concrete columns and found that, failure of hollow

members is strongly affected by the occurrence of premature mechanisms

(Compressed bars buckling and concrete cover spalling). The FRP

Confinement allows delaying these mechanisms, thus resulting in strength

improvements and significant ductility increases. The strength improvements

were more relevant in the case of specimens loads were eccentricity, whereas

the ductility improvements were more relevant in the case of bigger

eccentricity. The Ductility increases have been estimated through the

comparison of curvature ductility index and specific energy, the analysis of

curvature ductility indexes evidenced remarkable improvement of the seismic

response of the wrapped columns; after peak load carrying capabilities, which

was good energy dissipation.

Nagaradjane et al (2007) conducted an experiment on the plain

concrete cylinders of 150mm diameter that was cast using M30 grade

concrete out of which five specimens were wrapped with GFRP and it was

found that the increment in strength due to the application of GFRP wraps

ranged from 39.49% to 56.20%. Strengthening of Compression member using

GFRP wraps contributed very much to the increase in load carrying capacity

of columns. GFRP wrapping resulted in increase of axial strain capacity from

29

93.33% to 412.33% and lateral strain capacity from 785.68% to

1442.42%.Compared to the control specimen, GFRP confined specimen

exhibited higher axial and lateral strains at ultimate condition and lower axial

and lateral strains before failure. The application of GFRP confinement

contributed to the increase in compressive strength as well as ultimate strain

levels in the specimens. The improvement in strain capacity is more

pronounced than that in strength.

Yu-fei Wu et al (2008), made an attempt to find a new method of

retrofitting Square/ rectangular RC Column by embedding reinforcement bars

into the plastic hinge zone of the column. The author demonstrated that this

method was effective in delaying the concrete deterioration and in preventing

buckling of longitudinal reinforcement, and hence, is effective in increasing

the ductility and energy dissipation of the retrofitting columns.

Gnanasekaran Kaliyaperumal and Amlan Kumar Sengupta (2009)

conducted an experimental investigation on column specimens to study the

strength and they concluded that the retrofitted specimens did not show any

visible de-lamination between the existing concrete by motorized wire brush

was found to be satisfactory for the type of tests conducted. The moment

capacities of the retrofitted column specimens were substantially more than

those of the existing columns. This increase in capacities could be predicted

by analysis. The retrofitted beam -column- joint sub -assemblage specimens

showed substantial increase in lateral strength, ductility (i.e., energy

absorption) and energy dissipation.

Eid et al (2009) presented a test program that was designed to study

the behaviour of small-and large-scale normal and high strength concrete

circular column confined with transverse steel reinforcement, FRP, and both

transverse steel reinforcement and FRP under concentric loading. The test

results showed that the enhancement of the confined concrete strength and

30

strain was more pronounced in specimens with normal –strength concrete. It

is also shown that the rupture of the FRP in the specimens with higher

volumetric transverse steel reinforcement ratios corresponding to larger axial

compressive strength and strain, the post peak behaviour of these specimens is

more ductile.

Cui and Sheikh (2010) conducted an experiment on wrapped

columns and concluded that, strength enhancement effectiveness appears to

be independent of the amount of FRP when high modulus FRP is applied.

There is a minimum amount of FRP required to achieve strength

enhancement. This minimum requirement increases with unconfined concrete

strength and decreases with stiffness of FRP. Energy absorption capacity of

the specimens increased proportionally with the number of FRP layers and

was more pronounced for lower strength concretes. With the increase of the

concrete Strength, the energy absorption capacity decreased. The ductility

factor of confined concrete increased in proportion to the rupture strain of the

FRP jacket.

Antonio De Luca and Antonio Nanni (2011) analytically studied

the single parameter methodology for the prediction of the stress-strain

behaviour of FRP confined RC square columns and concluded that,

transverse/ diagonal dilation ratio -axial strain curves are influenced not only

by the modulus of elasticity and the thickness of the jacket but also by the

fibre type. However, it is believed that the validity of the theoretical

framework is independent from the fibre type.

2.5.6 Aramid Fibre Reinforced Polymer

Han Liang Wu et al (2009) studied the properties of high –strength

concrete (HSC) circular columns confined by Aramid Fibre Reinforced

Polymer (AFRP) sheets under axial compression. It was demonstrated that the

31

strength and ductility of the column with continuous AFRP wrapping

increased greatly, whereas the strength of the column with discontinuous

AFRP wrapping also increased, but the ductility not always increased notably.

The Compressive strength of the confined concrete columns improved as the

number of AFRP layers increased due confinement provided by continuous

AFRP wrapping. The improvement in compressive strength attributed to

AFRP sheet was greater when the concrete strength was lower.

2.6 NEED FOR PRESENT INVESTIGATION

In the past, research works have been carried out by researchers

with regard to the effect of FRP wrappings for a particular type of wrapping

and loading conditions. Not much work has been carried out in a single work

to find the effectiveness of CFRP, GFRP and Hybrid FRP wrapping for

different span to depth Ratios (L/D) of beams and height to least lateral

dimension (H/D) ratio of columns. Such a research shall lead to valuable

findings and comparative values.

2.7 OBJECTIVE AND SCOPE OF THE RESEARCH

The main objectives of the Research are

I. To study the effect of FRP wrapping (CFRP,GFRP and

Hybrid FRP) in retrofitting and rehabilitating RC beams for

different span to depth ratios to service load level in

comparison with control beams.

II. To study the effect of FRP wrapping (CFRP,GFRP and

Hybrid FRP) in retrofitting and rehabilitating RC beams for

different span to depth ratios to ultimate load level in

comparison with control beams.

32

III. To study the effect of FRP wrapping (CFRP,GFRP and

Hybrid FRP) in retrofitting and rehabilitating RC beams for

different span to depth ratios to ultimate load level in

comparison with control beams under cyclic loading.

IV. To study the effect of FRP wrapping (CFRP,GFRP and

Hybrid FRP) in retrofitting and rehabilitating RC columns for

different H/D ratios to ultimate load level in comparison with

control columns under uni -axial compression.

V. To study the effect of FRP Strip wrapping (CFRP,GFRP and

Hybrid FRP) in retrofitting and rehabilitating RC Columns for

different H/D ratios to ultimate load level in comparison with

control columns under uni axial compression.

2.8 METHODOLOGY

The following methodologies are adopted for beams and column

for this investigation

2.8.1 Beams

i) Control beams were tested to service load, ultimate load and

ultimate load level under cyclic loading.

ii) Control beams were retrofitted with CFRP, GFRP, HYBRID

FRP wrapping and tested to service load level.

iii) Control beams loaded to service level were rehabilitated with

CFRP, GFRP, HYBRID FRP wrapping and tested to service

load level.

33

iv) Control beams were retrofitted with CFRP, GFRP, HYBRID

FRP wrapping and tested to ultimate load level.

v) Control beams loaded to ultimate level were rehabilitated with

CFRP, GFRP, HYBRID FRP wrapping and tested to ultimate

load level.

vi) Control beams were retrofitted with CFRP, GFRP, HYBRID

FRP wrapping and tested to ultimate load level under cyclic

loading.

vii) Control beams loaded to ultimate level were rehabilitated with

CFRP, GFRP, HYBRID FRP wrapping and tested to ultimate

load level under cyclic loading.

2.8.2 Columns

1) Control columns were tested to ultimate load level under uni-

axial compression.

2) Control columns were retrofitted with CFRP, GFRP,

HYBRID FRP wrapping and tested to ultimate load level

under uni-axial compression.

3) Control columns loaded to ultimate level were rehabilitated

with CFRP, GFRP, HYBRID FRP wrapping and tested to

ultimate load level under uni-axial compression.

4) Control columns were retrofitted with CFRP, GFRP,

HYBRID FRP Strip wrapping and tested to ultimate load

level under uni-axial compression.