Research ArticleFlexural Behaviour of RC Beams Strengthened with PrestressedCFRP NSM Tendon Using New Prestressing System

Woo-tai Jung Jong-sup Park Jae-yoon Kang Moon-seoung Keum and Young-hwan Park

Structural Engineering Research Institute Korea Institute of Civil Engineering and Building Technology Goyang-si Republic of Korea

Correspondence should be addressed to Woo-tai Jung woodykictrekr

Received 21 February 2017 Accepted 14 June 2017 Published 17 July 2017

Academic Editor Peng He

Copyright copy 2017 Woo-tai Jung et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

CFRP has been used mainly for strengthening of existing structures in civil engineering area Prestressed strengthening is beingstudied to solve the bond failure model featuring EBR and NSMR methods The largest disadvantage of the prestressing systemis that the system cannot be removed until the filler is cured This problem lowers the turning rate of the equipment and makesit limited to experiment which stresses the necessity of a new prestressing system Therefore the present study applies a newprestressing systemwhich reliefs the need towait until the curing of the filler after jacking to the prestressing ofNSMRand examinesthe effect of the prestressing size and location of the anchorage on the strengthened behaviour The experimental results show thatthe crack and yield loads increase with higher level of prestress while the ductility tends to reduce and the anchor plate shouldbe installed within the effective depth 119889119904 to minimize the occurrence of shear-induced diagonal cracks The comparison of theexperimental results and results by section analysis shows that the section analysis could predict themaximum load of the specimensstrengthened by prestressed NSMR within an error between 4 and 6

1 Introduction

The conventional construction materials that are steel andconcrete have been exploited as the most popular anduniversal materials for the construction of structures to dateHowever the increase in length and size of recent structurestogether with the corrosion and heavy weight problemsinherent to these conventional materials surge the interestin alternative materials enabling us to supplement suchproblems Accordingly Carbon Fiber Reinforced Polymer(CFRP) is attracting attention as a construction materialenabling the replacement of the conventional steel materialsCFRP is a composite material fabricated by using polymerresin as matrix and fibers like carbon fiber as reinforcementCFRP exhibits outstanding resistance to corrosion and highstrength compared to its weight In the construction domainCFRP started to be used for the repair and strengthening ofstructures since late 1980s and has recently recognized widerexploitation by replacing steel reinforcement and tendons aswell as structural material for bridge decks in newly builtstructures [1ndash4]

Concrete structures degrade with time and the service-ability deteriorates following the ongoing performance lossof the concrete member and the material itself caused byenvironmental actions even though concrete has advantagesas construction material Externally bonded reinforcement(EBR) and near-surface mounted reinforcement (NSMR) arebeing studied as methods using CFRP for the strengtheningof degraded concrete structures EBR strengthens the con-crete member by bonding FRP sheet or plate on the tensileside of the member Besides NSMR operates by embeddingthe FRP reinforcement together with the filler in the slot thathas beenfirst arranged in the tensile side of the concrete coverIn terms of the efficiency of FRPNSMR is superior to EBRbutboth methods experience premature bond failure of the FRP-concrete interface before full development of the maximumperformance of FRP [5ndash7]

Studies attempted to overcome such drawback by pre-stressing the FRP reinforcement through the addition of ananchoring device to NSMR [8 9] Nordin and Taljsten [8]performed an experimental study by prestressing the CFRP(Carbon FRP) rod up to 10 and 20 of the yield strength

HindawiInternational Journal of Polymer ScienceVolume 2017 Article ID 1497349 9 pageshttpsdoiorg10115520171497349

2 International Journal of Polymer Science

Anchorage

FRP reinforcement

Hydraulic jack

AnchorageFRP reinforcement

Hydraulic jack

Specimen

Specimen

Figure 1 The existing prestressing system

The test results showed that the serviceability improved withsignificantly increased cracking and yield loads and that thedurability improved noticeably through enhanced fatiguebehaviour and smaller cracks [10] Jung et al [9] tensionedthe CFRP rod and plate up to 20 of the yield strengthand compared the behaviour with that of the NSMR withoutprestressing The authors reported that the introduction ofprestress could delay the bond failure since the prestressedNSMR specimens failed through the rupture of the FRPreinforcement [9] Badawi [11] compared the crack yield andmaximum loads of the NSMR specimen without prestressto those of NSMR specimens in which the CFRP rod wasprestressed up to 40 and 60 of the yield strength ofthe rod The specimen with prestressing of 40 exhibitedlarge increase of the crack yield and maximum loads butthe specimen with prestressing of 60 experienced slightreduction of the maximum load [11]

Many structures could fail at a lower load level than theirstatic capacity becausemost of themare under repeated loadsFatigue performance of the prestressed NSMRwould be gov-erned by conventional steels because CFRP reinforcementsoffer higher fatigue strength as compared with steel [12]However Badawi and Soudki [13] reported that the increasein CFRP prestress level results in a transition of the failuremode from steel fracture to CFRP rupture Oudah and El-Hacha [14] showed that the high prestress level resulted inan increased degradation and damage accumulation becausecyclic concrete creep deformation increasedwith the increasein the mean concrete cyclic stress

The studies related to the prestressed NSMR focusedmainly and experimentally on the prestressing force due tothe absence of appropriate prestressing system for NSMRThe prestressing systems applied in these experiments wereprincipally the pretensioning and the end-support systemsThe largest disadvantage of the prestressing system is thatthe system cannot be removed until the filler is cured Thisproblem lowers the turning rate of the equipment and makesit limited to experiment which stresses the necessity of a newprestressing system (Figure 1) [15]

Therefore this study applies a new prestressing systemwhich reliefs the need to wait until the curing of the filler after

Table 1 Summary of material properties

Material PropertiesConcrete(1) Compressive strength (MPa) 27

Tension steel reinforcement(D10)(1)

Yield strength (MPa) 426Tensile strength (MPa) 562

Diameter (mm) 953Area (cm2) 07133

Compression steelreinforcement (D13)(1)

Yield strength (MPa) 481Tensile strength (MPa) 608

Diameter (mm) 127Area (cm2) 1267

Epoxy(2)Bond strength (MPa) 361

Compressive strength (MPa) 112Flexural strength (MPa) 637

CFRP tendon(Circular type)(1)

Diameter (mm) 95Tensile strength (MPa) 2500Elastic modulus (GPa) 135

(1) from tests carried out by the authors (2) provided by supplier

jacking to the prestressing of NSMR and examines the effectof the prestressing size and location of the anchorage on thestrengthened behaviour

2 Experimental Program

21 Manufacture of Specimens A total of 8 simply supportedRCbeam specimenswith span of 3mwere cast using concretewith compressive strength of 27MPa at 28 days with thedetails and cross-section shown in Figure 2 SD400 steel barsD10 (120601953mm) are arranged with steel ratio of 00041 onelayer of threeD13 bars (120601127mm) is arranged as compressionreinforcements D10 shear bars are disposed every 100mm inthe shear zone to prevent shear failure and CFRP tendons areused being 95mm diameter in Figure 3 Table 1 summarizesthe properties of the materials used in the test beams

International Journal of Polymer Science 3

Table 2 Experimental parameters

Specimens Strengthened length (mm) 119871 119904119871 Filler Prestressing levelControl mdash mdash mdash mdashSL90-E-0 2700 090 Epoxy 0SL90-E-20 2700 090 Epoxy 20SL90-E-40 2700 090 Epoxy 40SL70-E-50 2100 070 Epoxy 50SL83-E-40 2500 083 Epoxy 40SL77-E-40 2300 077 Epoxy 40SL70-E-40 2100 070 Epoxy 40

300 30

30

3ea-D13

3ea-D10

Stirrup D10100

200

300

200 3000 200

3400

1050 900 1050

300

150150 150150100 100

P2 P2

Figure 2 Details and cross-section of specimens (mm)

Figure 3 Shape of CFRP tendon

22 Experimental Parameters Since prestressed NSMRintroduces prestress to improve actively the performancebased upon the behaviour of NSMR its behaviour is closelyrelated to that of NSMR Among the factors influencingthe strengthening performance of NSMR the length ofstrengthening is an important one related to the failuremode which has been frequently adopted as test variablebecause it is easy to implement [9 15] Even if this lengthof strengthening influences the strengthening performanceof the NSMR including the prestressed NSMR the researchresults published to date could not evaluate the effect of thelength of strengthening since this length was longer than thespan length due to the absence of appropriate jacking systemTherefore research should be further on this topic

Research also compared experimentally the strength-ening performance applying inorganic cement grout [16]despite the fact that organic epoxy is mainly used as filler

in current NSMR The authors reported that cement isstill inappropriate to replace epoxy and related the possibleapplicability of materials with superior properties like highstrengthmortar as replacement of epoxyMoreover consider-ing the high cost of epoxy compared tomortar need is for fur-ther investigation on the strengthening performance broughtby the relatively cheaper mortar Accordingly this studyapplies a newly developed prestressing system to prestressedNSMR to conduct experiments considering the length ofstrengthening the introduced prestress force (Table 2) Thelength of strengthening is varied from 70 to 90 of the spanlength and the prestress force is varied to be 0 20 40and 50 of the tensile strength of the CFRP reinforcementEpoxy is adopted as filler to observe the static performanceand failure pattern of the specimens

Table 2 lists the experimental parameters and corre-sponding designations of the specimens The control speci-men as the beamwithout strengthening was cast to comparethe strengthening performance of the NSM systems Themain variables of this study are the prestressing level andthe length of strengthening (Table 2) The prestressing levelscorrespond to 0 20 and 40 of tensile strength of theNSM CFRP tendon

23 Prestressing of NSMR Figures 4 and 5 illustrate the newprestressing system developed in this study As shown inFigure 4(a) the CFRP tendon installed in the anchorage isfixed by fastening nuts on the anchoring plates in the fixedend and jacked end Then the jacking frame is installed onthe anchoring plate at the jacked end to proceed prestressing

4 International Journal of Polymer Science

Table 3 Summary of experimental results

Yielding MaximumFailure mode 119889119906119889119910119872119910

kNmm119875119910kN

119889119910mm 119875119875119910 con 119872119906

kNmm119875119906kN

119889119906mm 119875119875119906 con

Control-27MPa 23006 4382 1152 1 25799 4914 4649 1 a 403SL90-E-0 33448 6371 1382 145 59220 1128 6189 23 b 448SL90-E-20 41528 791 1536 181 62543 11913 5378 242 b 35SL90-E-40 47345 9018 1608 206 62029 11815 3846 24 b 239SL70-E-50 52889 10074 1809 23 62606 11925 3848 243 b c 213SL83-E-40 49009 9335 155 213 67032 12768 4304 26 b 278SL77-E-40 48269 9194 1783 21 67872 12928 4637 263 c 26SL70-E-40 48878 931 1799 212 60344 11494 4509 234 c 251a flexural failure b rupture of CFRP tendon c increased cracking of anchor plate

Anchorage plate

CFRP tendon

(a)

Prestressing system

(b)

Filler

(c)

Figure 4 Concept of the new prestressing system developed in this study

Making groove CFRP tendon Anchorage plate

Anchoring by nut

Prestressing system

Prestressing

Removing prestressing system Filling amp curing filler

Figure 5 Application of the new prestressing system

after having installed the hydraulic cylinder as shown inFigure 4(b)Thereafter the anchored end of the CFRP tendonis nut-fastened and prestressing is completed by removing thepressure of the hydraulic cylinder Finally the anchorage isdismantled before filling the groove with the filler and curingthe filler (Figure 4(c))

24 Loading and Measurement Methods All the specimenswere subjected to 4-point bending tests up to failure bymeansof a UTM (Universal Testing Machine) with capacity of

980 kNThe loading was applied under displacement controlat speed of 002mmsec until the first 10mmand005mmsecfrom 10mm until failure The test data were recorded by astatic data logger and a computer at intervals of 1 secondElectrical resistance strain gauges were fixed at mid-span and1198714 to measure the strain of steel reinforcements

3 Experimental Results31 Failure Modes and Strengthening Performances Table 3arranges the experimental results

International Journal of Polymer Science 5

Figure 6 Rupture of CFRP tendon (SL90-E-40)

Figure 7 Cracking of anchor plate (SL70-E-40)

Themoment load anddeflection are represented for eachrebar yielding and maximum load PP_con the load ratioof strengthened specimen to the nonstrengthened specimen(CONTROL) indicates the strengthening effect 119889119906119889119910 thedeflection ratio of maximum to yielding shows the ductil-ity of specimen The control specimen exhibited commonflexure failure occurring through compressive failure of theupper concrete after yielding of the reinforcement Besidesthe prestressed NSM specimens experienced two types offailure mode by rupture of the CFRP tendon after yielding ofthe steel reinforcement (SL90 SL83 Figure 6) and by increaseof the cracks around the anchor plate (SL77 SL70 Figure 7)

32 Strengthening Performance Figure 8 plots the load-deflection curves according to the level of prestressThe crackload and yield load are seen to increase with higher level ofprestress Since the rupture of the CFRP tendon determinesthe member performance similar maximum load can beobserved regardless of the level of prestress and the ductilityappears to reduce In view of the strengthening performancewith respect to the level of prestress the yield load and themaximum load are seen to increase respectively by 45 to130 and by 113 to 143 compared to the control specimen

Figure 9 compares the load-deflection curves accordingto the length of strengthening Since all the consideredspecimens were prestressed up to 40 of the tensile strengthof the CFRP tendon similar crack load yield load andmaximum load can be observedThe ductility tends to reducewith reference to specimen SL83 and can be attributed to

Deflection (mm)0 20 40 60 80

Load

(kN

)

0

20

40

60

80

100

120

140

SL90-E-0SL90-E-20

SL90-E-40SL70-E-50

Control 27－Ｊ

Figure 8 Experimental load-deflection curves

Deflection (mm)0 20 40 60 80

Load

(kN

)

0

20

40

60

80

100

120

140

SL90-E-40SL83-E-40

SL77-E-40SL70-E-40

Control-27－Ｊ

Figure 9 Experimental load-deflection curves

the occurrence of cracks around the anchor plate If thelocation of the anchor plate falls outside the effective depth 119889119904and the length of strengthening shortens the cracks increasearound the anchor plate after yielding of the tensile steeland appears to lower the maximum load since the anchorbecomes insufficient for the rupture of the CFRP tendon

4 Analytical and Experimental Results

41 Section Analysis of Specimens Reinforced by PrestressedNSMR Numerous researchers proposed bond failure mod-els to predict the behaviour of the specimens reinforced byNSMR [16ndash18] However for the prestressed NSMR withanchorage it is impossible to predict the behaviour by sectionanalysis without a complex bond failure model since rupture

6 International Journal of Polymer Science

b

h

c

Initial prestressing

PrestressedNSM

NAdf

ds

sf3

t

f2 f1

fe = f1 + f2 + f3

s

c

fs

ffe

ft

fc

fs

ds

(a)

PrestressedNSM

b

h

c

NA

Initial prestressing

dfds

s

f3 f2f1

fe = f1 + f2 + f3

s

c

fs

ffe

fc

fs

ds

(b)

b

h

cNA

Initial prestressing

PrestressedNSM

df

ds

s

f3 f2 f1

fe = f1 + f2 + f3

s

c

fs

ffe

fc

fs

ds

(c)

Figure 10 Load-deflection curves per analysis stage

of the CFRP tendon occurs when reaching the maximumperformance of the material

Accordingly this study conducts section analysis usingthe strain compatibility and force equilibrium conditions forfurther comparison with the experimental behaviour of thespecimens strengthened by prestressed NSMRThemoment-curvature distribution of the normal concrete specimens canbe subdivided into three stages limited by the initiation ofcracking and the yielding of steel Therefore section analysisis also conducted by distinguishing the working moment bymeans of the load for the stages before cracking after crackingand before yielding of steel and after yielding of steel [11 19]

The calculation at each stage uses the equilibrium conditionsof the forces and moments Figure 10 depicts the distributionof the strain and stress at each stage

(a) Precracking stage is as follows 0 le 119872119886 le 11987211988811990312119891119888119887119888 + 119860

10158401199041198911015840119904 minus 12 (ℎ minus 119888) 119891119888119905119887 minus 119860 119904119891119904 minus 119860119891119891119891119890 = 0

119872119886= 13119891119888119905119887ℎ (ℎ minus 119888) + 119860 119904119891119904 (119889119904 minus

13119888)

+ 119860119891119891119891119890 (119889119891 minus 13119888) minus 11986010158401199041198911015840119904 (13119888 minus 119889

1015840119904)

(1)

International Journal of Polymer Science 7

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

(a) SL90-E-0

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

(b) SL90-E-20

0

20

40

60

80

100

120

140

0 20 40 60 80Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

FRP rupture

(c) SL90-E-40

Deflection (mm)

Load

(kN

)

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

ExperimentalAnalytical

(d) SL70-E-50

Figure 11 Comparison of experimental and analytical load-deflection curves

(b) Preyielding stage is as follows119872119888119903 le 119872119886 le 11987211991012057211205731119891119888119896119887119888 + 11986010158401199041198911015840119904 minus 119860 119904119891119904 minus 119860119891119891119891119890 = 0119872119886= 119860 119904119891119904 (119889119904 minus 121205731119888) + 119860119891119891119891119890 (119889119891 minus

121205731119888)

minus 11986010158401199041198911015840119904 (121205731119888 minus 1198891015840119904)

(2)

(c) Postyielding stage is as follows119872119910 le 119872119886 le 11987211990612057211205731119891119888119896119887119888 + 11986010158401199041198911015840119904 minus 119860 119904 [119891119910 + 1198641015840119904 (120576119904 minus 120576119910)] minus 119860119891119891119891119890= 0119872119886= 119860 119904 [119891119910 + 1198641015840119904 (120576119904 minus 120576119910)] (119889119904 minus 121205731119888)

+ 119860119891119891119891119890 (119889119891 minus 121205731119888) minus 11986010158401199041198911015840119904 (121205731119888 minus 119889

1015840119904)

(3)

42 Calculation Process The calculation determines thedeflection the strain of each material the loads and theposition of the neutral axis by the strain compatibility con-dition while increasing the strain of steel by the constitutiveequations of each material and by the equilibrium of theinternal forces The final failure mode is decided to be thecompressive failure of concrete if the compressive strain ofthe concrete at the top exceeds 0003 or the rupture of theCFRP tendon when exceeding the rupture strain of CFRP

43 Comparison of Analytical and Experimental Results Fig-ures 11 and 12 compare the analytical and experimental resultswith respect to the level of prestressThe analytical predictionof the load-deflection relation is seen to be in good agreementwith the experimental results for the specimens strengthenedby NSMR with prestress levels up to 0 20 40 and50 In particular the maximum load of the specimens withprestress levels of 20 40 and 50 is predicted within anerror running between 4 and 6 Besides the maximumload of the specimen with 0 of prestress is predicted with

8 International Journal of Polymer Science

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(a) SL90-E-0

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(b) SL90-E-20

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(c) SL90-E-40

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(d) SL70-E-50

Figure 12 Comparison of experimental and analytical load-strain curves

an error between 6 and 8 This slightly larger error is dueto the occurrence of local failure at the bottom concrete underthe loaded point (Figure 12(a))

5 Conclusions

This study examined the flexural behaviour of specimensstrengthened by prestressed NSM CFRP tendon The follow-ing conclusions can be drawn

(1) The crack and yield loads increased with higherlevel of prestress but the ductility tended to reduceThe specimens in which failure occurred throughthe rupture of the CFRP tendon showed similarmaximum load

(2) The analysis of the failure mode with respect tothe length of strengthening showed that the failurepattern and cracking pattern varied according to theposition of the anchor plate Flexural failure could be

induced by installing the anchor plate closest to thesupport The experimental results revealed that theanchor plate should be installed within the effectivedepth119889119904 tominimize the occurrence of shear-induceddiagonal cracksThe test results also indicated that thelength ratio of strengthening should be larger than83 to prevent the occurrence of bond failure at theend of the reinforcement

(3) The comparison of the analytical and experimentalresults showed that the section analysis could predictthe maximum load of the specimens strengthened byprestressed NSMR within an error between 4 and6

Conflicts of Interest

The authors declare that they have no conflicts of interest

International Journal of Polymer Science 9

Acknowledgments

This research was supported by a grant from ldquoa StrategicResearch Project funded by the Korea Institute of CivilEngineering and Building Technologyrdquo and ldquoUpgradingTechnology of Prestressed NSM Reinforcement System withCFRP Tendonrdquo

References

[1] M Rezazadeh H Ramezansefat and J Barros ldquoNSM CFRPprestressing techniques with strengthening potential for simul-taneously enhancing load capacity and ductility performancerdquoJournal of Composites for Construction vol 20 no 5 Article ID04016029 2016

[2] W T Jung J S Park and Y H Park ldquoAn experimental study onapplication of new prestressing system for NSM strengtheningtechniquerdquo inProceedings of the 9th International Symposium onFiber Reinforced Polymer Reinforcement for Reinforced ConcreteStructures (FRPRCSrsquo09) 2009

[3] W-T Jung J-S Park and S-H Kim ldquoA study on the behav-ior characteristics of curved FRP-concrete composite panelrdquoAdvanced Materials Research vol 557-559 pp 375ndash380 2012

[4] J S Park Y H Park I J Kwak W T Jung and S Y ChoildquoA Study on FRP Cable System for Cable Stayed Bridgerdquo RampDReport 08 Super-Long Span Bridge C02-01 Korea Institute ofConstruction Technology 2011

[5] W Jung J Park J Kang and M Keum ldquoFlexural behaviorof concrete beam strengthened by near-surface mounted cfrpreinforcement using equivalent section modelrdquo Advances inMaterials Science and Engineering vol 2017 pp 1ndash16 2017

[6] R EI-Hacha ldquoEffectiveness of near surface mounted frp rein-forcement for flexural strengthening of reinforced concretebeamsrdquo in Proceedings of the 4th International Conferenceon Advanced Composite Materials in Bridges and StructuresAlberta Canada 2004

[7] L De Lorenzis and J G Teng ldquoNear-surface mounted FRPreinforcement an emerging technique for strengthening struc-turesrdquoComposites Part B Engineering vol 38 no 2 pp 119ndash1432007

[8] H Nordin and B Taljsten ldquoConcrete beams strengthened withprestressed near surface mounted CFRPrdquo Journal of Compositesfor Construction vol 10 no 1 pp 60ndash68 2006

[9] W T Jung Y H Park and J S Park ldquoA study on the flexuralbehavior of reinforced concrete beams strengthened with NSMprestressed CFRP reinforcementsrdquo in Proceedings of the 8thInternational Symposium on FRP Reinforcement for ConcreteStructures (FRPRCSrsquo08) Patras Greece 2007

[10] H Nordin Flexural Strengthening of Concrete Structures withPrestressed Near Surface Mounted CFRP Rods Lulea Universityof Technology 2003

[11] M A BadawiMonotonic and Fatigue Flexural Behaviour of RCBeams Strengthened with Prestressed NSM CFRP Rods [PhDthesis] University of Waterloo Waterloo Ontario Canada2007

[12] R El-Hacha and K Soudki ldquoPrestressed near-surface mountedfibre reinforced polymer reinforcement for concrete structures- A reviewrdquo Canadian Journal of Civil Engineering vol 40 no11 pp 1127ndash1139 2013

[13] M Badawi and K Soudki ldquoFatigue behavior of RC beamsstrengthened with NSM CFRP rodsrdquo Journal of Composites forConstruction vol 13 no 5 pp 415ndash421 2009

[14] FOudah andR El-Hacha ldquoPerformance of RCbeams strength-ened using prestressed NSM-CFRP strips subjected to fatigueloadingrdquo Journal of Composites for Construction vol 16 no 3pp 300ndash307 2012

[15] KICT ldquoDevelopment of Bridge Strengthening Methods usingPrestressed FRP Compositesrdquo Tech Rep 2015

[16] T Hassan and S Rizkalla ldquoInvestigation of bond in concretestructures strengthened with near surface mounted carbonfiber reinforced polymer stripsrdquo Journal of Composites forConstruction vol 7 no 3 pp 248ndash257 2003

[17] M Blaschko ldquoBond Behavior of Strips Glued into Slitsrdquo inFRPRCS-6 pp 205ndash214 World Scientific Singapore 2003

[18] W T Jung Flexural Behavior of Reinforced Concrete BeamsStrengthened with NSM CFRP Reinforcements Considering theEquivalent Section [PhD thesis] Myongji University SeoulKorea 2009

[19] J S Park W T Jung Y H Park and C Y ldquoThe analysisfor reinforced concrete beams strengthened with externallyunbonded prestressed CFRP platesrdquo Journal of the Korea Societyof Civil Engineers vol 28 no 4A pp 439ndash445 2008

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International Journal of Polymer Science 3

Table 2 Experimental parameters

Specimens Strengthened length (mm) 119871 119904119871 Filler Prestressing levelControl mdash mdash mdash mdashSL90-E-0 2700 090 Epoxy 0SL90-E-20 2700 090 Epoxy 20SL90-E-40 2700 090 Epoxy 40SL70-E-50 2100 070 Epoxy 50SL83-E-40 2500 083 Epoxy 40SL77-E-40 2300 077 Epoxy 40SL70-E-40 2100 070 Epoxy 40

300 30

30

3ea-D13

3ea-D10

Stirrup D10100

200

300

200 3000 200

3400

1050 900 1050

300

150150 150150100 100

P2 P2

Figure 2 Details and cross-section of specimens (mm)

Figure 3 Shape of CFRP tendon

22 Experimental Parameters Since prestressed NSMRintroduces prestress to improve actively the performancebased upon the behaviour of NSMR its behaviour is closelyrelated to that of NSMR Among the factors influencingthe strengthening performance of NSMR the length ofstrengthening is an important one related to the failuremode which has been frequently adopted as test variablebecause it is easy to implement [9 15] Even if this lengthof strengthening influences the strengthening performanceof the NSMR including the prestressed NSMR the researchresults published to date could not evaluate the effect of thelength of strengthening since this length was longer than thespan length due to the absence of appropriate jacking systemTherefore research should be further on this topic

Research also compared experimentally the strength-ening performance applying inorganic cement grout [16]despite the fact that organic epoxy is mainly used as filler

in current NSMR The authors reported that cement isstill inappropriate to replace epoxy and related the possibleapplicability of materials with superior properties like highstrengthmortar as replacement of epoxyMoreover consider-ing the high cost of epoxy compared tomortar need is for fur-ther investigation on the strengthening performance broughtby the relatively cheaper mortar Accordingly this studyapplies a newly developed prestressing system to prestressedNSMR to conduct experiments considering the length ofstrengthening the introduced prestress force (Table 2) Thelength of strengthening is varied from 70 to 90 of the spanlength and the prestress force is varied to be 0 20 40and 50 of the tensile strength of the CFRP reinforcementEpoxy is adopted as filler to observe the static performanceand failure pattern of the specimens

Table 2 lists the experimental parameters and corre-sponding designations of the specimens The control speci-men as the beamwithout strengthening was cast to comparethe strengthening performance of the NSM systems Themain variables of this study are the prestressing level andthe length of strengthening (Table 2) The prestressing levelscorrespond to 0 20 and 40 of tensile strength of theNSM CFRP tendon

23 Prestressing of NSMR Figures 4 and 5 illustrate the newprestressing system developed in this study As shown inFigure 4(a) the CFRP tendon installed in the anchorage isfixed by fastening nuts on the anchoring plates in the fixedend and jacked end Then the jacking frame is installed onthe anchoring plate at the jacked end to proceed prestressing

4 International Journal of Polymer Science

Table 3 Summary of experimental results

Yielding MaximumFailure mode 119889119906119889119910119872119910

kNmm119875119910kN

119889119910mm 119875119875119910 con 119872119906

kNmm119875119906kN

119889119906mm 119875119875119906 con

Control-27MPa 23006 4382 1152 1 25799 4914 4649 1 a 403SL90-E-0 33448 6371 1382 145 59220 1128 6189 23 b 448SL90-E-20 41528 791 1536 181 62543 11913 5378 242 b 35SL90-E-40 47345 9018 1608 206 62029 11815 3846 24 b 239SL70-E-50 52889 10074 1809 23 62606 11925 3848 243 b c 213SL83-E-40 49009 9335 155 213 67032 12768 4304 26 b 278SL77-E-40 48269 9194 1783 21 67872 12928 4637 263 c 26SL70-E-40 48878 931 1799 212 60344 11494 4509 234 c 251a flexural failure b rupture of CFRP tendon c increased cracking of anchor plate

Anchorage plate

CFRP tendon

(a)

Prestressing system

(b)

Filler

(c)

Figure 4 Concept of the new prestressing system developed in this study

Making groove CFRP tendon Anchorage plate

Anchoring by nut

Prestressing system

Prestressing

Removing prestressing system Filling amp curing filler

Figure 5 Application of the new prestressing system

after having installed the hydraulic cylinder as shown inFigure 4(b)Thereafter the anchored end of the CFRP tendonis nut-fastened and prestressing is completed by removing thepressure of the hydraulic cylinder Finally the anchorage isdismantled before filling the groove with the filler and curingthe filler (Figure 4(c))

24 Loading and Measurement Methods All the specimenswere subjected to 4-point bending tests up to failure bymeansof a UTM (Universal Testing Machine) with capacity of

980 kNThe loading was applied under displacement controlat speed of 002mmsec until the first 10mmand005mmsecfrom 10mm until failure The test data were recorded by astatic data logger and a computer at intervals of 1 secondElectrical resistance strain gauges were fixed at mid-span and1198714 to measure the strain of steel reinforcements

3 Experimental Results31 Failure Modes and Strengthening Performances Table 3arranges the experimental results

International Journal of Polymer Science 5

Figure 6 Rupture of CFRP tendon (SL90-E-40)

Figure 7 Cracking of anchor plate (SL70-E-40)

Themoment load anddeflection are represented for eachrebar yielding and maximum load PP_con the load ratioof strengthened specimen to the nonstrengthened specimen(CONTROL) indicates the strengthening effect 119889119906119889119910 thedeflection ratio of maximum to yielding shows the ductil-ity of specimen The control specimen exhibited commonflexure failure occurring through compressive failure of theupper concrete after yielding of the reinforcement Besidesthe prestressed NSM specimens experienced two types offailure mode by rupture of the CFRP tendon after yielding ofthe steel reinforcement (SL90 SL83 Figure 6) and by increaseof the cracks around the anchor plate (SL77 SL70 Figure 7)

32 Strengthening Performance Figure 8 plots the load-deflection curves according to the level of prestressThe crackload and yield load are seen to increase with higher level ofprestress Since the rupture of the CFRP tendon determinesthe member performance similar maximum load can beobserved regardless of the level of prestress and the ductilityappears to reduce In view of the strengthening performancewith respect to the level of prestress the yield load and themaximum load are seen to increase respectively by 45 to130 and by 113 to 143 compared to the control specimen

Figure 9 compares the load-deflection curves accordingto the length of strengthening Since all the consideredspecimens were prestressed up to 40 of the tensile strengthof the CFRP tendon similar crack load yield load andmaximum load can be observedThe ductility tends to reducewith reference to specimen SL83 and can be attributed to

Deflection (mm)0 20 40 60 80

Load

(kN

)

0

20

40

60

80

100

120

140

SL90-E-0SL90-E-20

SL90-E-40SL70-E-50

Control 27－Ｊ

Figure 8 Experimental load-deflection curves

Deflection (mm)0 20 40 60 80

Load

(kN

)

0

20

40

60

80

100

120

140

SL90-E-40SL83-E-40

SL77-E-40SL70-E-40

Control-27－Ｊ

Figure 9 Experimental load-deflection curves

the occurrence of cracks around the anchor plate If thelocation of the anchor plate falls outside the effective depth 119889119904and the length of strengthening shortens the cracks increasearound the anchor plate after yielding of the tensile steeland appears to lower the maximum load since the anchorbecomes insufficient for the rupture of the CFRP tendon

4 Analytical and Experimental Results

41 Section Analysis of Specimens Reinforced by PrestressedNSMR Numerous researchers proposed bond failure mod-els to predict the behaviour of the specimens reinforced byNSMR [16ndash18] However for the prestressed NSMR withanchorage it is impossible to predict the behaviour by sectionanalysis without a complex bond failure model since rupture

6 International Journal of Polymer Science

b

h

c

Initial prestressing

PrestressedNSM

NAdf

ds

sf3

t

f2 f1

fe = f1 + f2 + f3

s

c

fs

ffe

ft

fc

fs

ds

(a)

PrestressedNSM

b

h

c

NA

Initial prestressing

dfds

s

f3 f2f1

fe = f1 + f2 + f3

s

c

fs

ffe

fc

fs

ds

(b)

b

h

cNA

Initial prestressing

PrestressedNSM

df

ds

s

f3 f2 f1

fe = f1 + f2 + f3

s

c

fs

ffe

fc

fs

ds

(c)

Figure 10 Load-deflection curves per analysis stage

of the CFRP tendon occurs when reaching the maximumperformance of the material

Accordingly this study conducts section analysis usingthe strain compatibility and force equilibrium conditions forfurther comparison with the experimental behaviour of thespecimens strengthened by prestressed NSMRThemoment-curvature distribution of the normal concrete specimens canbe subdivided into three stages limited by the initiation ofcracking and the yielding of steel Therefore section analysisis also conducted by distinguishing the working moment bymeans of the load for the stages before cracking after crackingand before yielding of steel and after yielding of steel [11 19]

The calculation at each stage uses the equilibrium conditionsof the forces and moments Figure 10 depicts the distributionof the strain and stress at each stage

(a) Precracking stage is as follows 0 le 119872119886 le 11987211988811990312119891119888119887119888 + 119860

10158401199041198911015840119904 minus 12 (ℎ minus 119888) 119891119888119905119887 minus 119860 119904119891119904 minus 119860119891119891119891119890 = 0

119872119886= 13119891119888119905119887ℎ (ℎ minus 119888) + 119860 119904119891119904 (119889119904 minus

13119888)

+ 119860119891119891119891119890 (119889119891 minus 13119888) minus 11986010158401199041198911015840119904 (13119888 minus 119889

1015840119904)

(1)

International Journal of Polymer Science 7

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

(a) SL90-E-0

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

(b) SL90-E-20

0

20

40

60

80

100

120

140

0 20 40 60 80Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

FRP rupture

(c) SL90-E-40

Deflection (mm)

Load

(kN

)

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

ExperimentalAnalytical

(d) SL70-E-50

Figure 11 Comparison of experimental and analytical load-deflection curves

(b) Preyielding stage is as follows119872119888119903 le 119872119886 le 11987211991012057211205731119891119888119896119887119888 + 11986010158401199041198911015840119904 minus 119860 119904119891119904 minus 119860119891119891119891119890 = 0119872119886= 119860 119904119891119904 (119889119904 minus 121205731119888) + 119860119891119891119891119890 (119889119891 minus

121205731119888)

minus 11986010158401199041198911015840119904 (121205731119888 minus 1198891015840119904)

(2)

(c) Postyielding stage is as follows119872119910 le 119872119886 le 11987211990612057211205731119891119888119896119887119888 + 11986010158401199041198911015840119904 minus 119860 119904 [119891119910 + 1198641015840119904 (120576119904 minus 120576119910)] minus 119860119891119891119891119890= 0119872119886= 119860 119904 [119891119910 + 1198641015840119904 (120576119904 minus 120576119910)] (119889119904 minus 121205731119888)

+ 119860119891119891119891119890 (119889119891 minus 121205731119888) minus 11986010158401199041198911015840119904 (121205731119888 minus 119889

1015840119904)

(3)

42 Calculation Process The calculation determines thedeflection the strain of each material the loads and theposition of the neutral axis by the strain compatibility con-dition while increasing the strain of steel by the constitutiveequations of each material and by the equilibrium of theinternal forces The final failure mode is decided to be thecompressive failure of concrete if the compressive strain ofthe concrete at the top exceeds 0003 or the rupture of theCFRP tendon when exceeding the rupture strain of CFRP

43 Comparison of Analytical and Experimental Results Fig-ures 11 and 12 compare the analytical and experimental resultswith respect to the level of prestressThe analytical predictionof the load-deflection relation is seen to be in good agreementwith the experimental results for the specimens strengthenedby NSMR with prestress levels up to 0 20 40 and50 In particular the maximum load of the specimens withprestress levels of 20 40 and 50 is predicted within anerror running between 4 and 6 Besides the maximumload of the specimen with 0 of prestress is predicted with

8 International Journal of Polymer Science

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(a) SL90-E-0

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(b) SL90-E-20

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(c) SL90-E-40

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(d) SL70-E-50

Figure 12 Comparison of experimental and analytical load-strain curves

an error between 6 and 8 This slightly larger error is dueto the occurrence of local failure at the bottom concrete underthe loaded point (Figure 12(a))

5 Conclusions

This study examined the flexural behaviour of specimensstrengthened by prestressed NSM CFRP tendon The follow-ing conclusions can be drawn

(1) The crack and yield loads increased with higherlevel of prestress but the ductility tended to reduceThe specimens in which failure occurred throughthe rupture of the CFRP tendon showed similarmaximum load

(2) The analysis of the failure mode with respect tothe length of strengthening showed that the failurepattern and cracking pattern varied according to theposition of the anchor plate Flexural failure could be

induced by installing the anchor plate closest to thesupport The experimental results revealed that theanchor plate should be installed within the effectivedepth119889119904 tominimize the occurrence of shear-induceddiagonal cracksThe test results also indicated that thelength ratio of strengthening should be larger than83 to prevent the occurrence of bond failure at theend of the reinforcement

(3) The comparison of the analytical and experimentalresults showed that the section analysis could predictthe maximum load of the specimens strengthened byprestressed NSMR within an error between 4 and6

Conflicts of Interest

The authors declare that they have no conflicts of interest

International Journal of Polymer Science 9

Acknowledgments

This research was supported by a grant from ldquoa StrategicResearch Project funded by the Korea Institute of CivilEngineering and Building Technologyrdquo and ldquoUpgradingTechnology of Prestressed NSM Reinforcement System withCFRP Tendonrdquo

References

[1] M Rezazadeh H Ramezansefat and J Barros ldquoNSM CFRPprestressing techniques with strengthening potential for simul-taneously enhancing load capacity and ductility performancerdquoJournal of Composites for Construction vol 20 no 5 Article ID04016029 2016

[2] W T Jung J S Park and Y H Park ldquoAn experimental study onapplication of new prestressing system for NSM strengtheningtechniquerdquo inProceedings of the 9th International Symposium onFiber Reinforced Polymer Reinforcement for Reinforced ConcreteStructures (FRPRCSrsquo09) 2009

[3] W-T Jung J-S Park and S-H Kim ldquoA study on the behav-ior characteristics of curved FRP-concrete composite panelrdquoAdvanced Materials Research vol 557-559 pp 375ndash380 2012

[4] J S Park Y H Park I J Kwak W T Jung and S Y ChoildquoA Study on FRP Cable System for Cable Stayed Bridgerdquo RampDReport 08 Super-Long Span Bridge C02-01 Korea Institute ofConstruction Technology 2011

[5] W Jung J Park J Kang and M Keum ldquoFlexural behaviorof concrete beam strengthened by near-surface mounted cfrpreinforcement using equivalent section modelrdquo Advances inMaterials Science and Engineering vol 2017 pp 1ndash16 2017

[6] R EI-Hacha ldquoEffectiveness of near surface mounted frp rein-forcement for flexural strengthening of reinforced concretebeamsrdquo in Proceedings of the 4th International Conferenceon Advanced Composite Materials in Bridges and StructuresAlberta Canada 2004

[7] L De Lorenzis and J G Teng ldquoNear-surface mounted FRPreinforcement an emerging technique for strengthening struc-turesrdquoComposites Part B Engineering vol 38 no 2 pp 119ndash1432007

[8] H Nordin and B Taljsten ldquoConcrete beams strengthened withprestressed near surface mounted CFRPrdquo Journal of Compositesfor Construction vol 10 no 1 pp 60ndash68 2006

[9] W T Jung Y H Park and J S Park ldquoA study on the flexuralbehavior of reinforced concrete beams strengthened with NSMprestressed CFRP reinforcementsrdquo in Proceedings of the 8thInternational Symposium on FRP Reinforcement for ConcreteStructures (FRPRCSrsquo08) Patras Greece 2007

[10] H Nordin Flexural Strengthening of Concrete Structures withPrestressed Near Surface Mounted CFRP Rods Lulea Universityof Technology 2003

[11] M A BadawiMonotonic and Fatigue Flexural Behaviour of RCBeams Strengthened with Prestressed NSM CFRP Rods [PhDthesis] University of Waterloo Waterloo Ontario Canada2007

[12] R El-Hacha and K Soudki ldquoPrestressed near-surface mountedfibre reinforced polymer reinforcement for concrete structures- A reviewrdquo Canadian Journal of Civil Engineering vol 40 no11 pp 1127ndash1139 2013

[13] M Badawi and K Soudki ldquoFatigue behavior of RC beamsstrengthened with NSM CFRP rodsrdquo Journal of Composites forConstruction vol 13 no 5 pp 415ndash421 2009

[14] FOudah andR El-Hacha ldquoPerformance of RCbeams strength-ened using prestressed NSM-CFRP strips subjected to fatigueloadingrdquo Journal of Composites for Construction vol 16 no 3pp 300ndash307 2012

[15] KICT ldquoDevelopment of Bridge Strengthening Methods usingPrestressed FRP Compositesrdquo Tech Rep 2015

[16] T Hassan and S Rizkalla ldquoInvestigation of bond in concretestructures strengthened with near surface mounted carbonfiber reinforced polymer stripsrdquo Journal of Composites forConstruction vol 7 no 3 pp 248ndash257 2003

[17] M Blaschko ldquoBond Behavior of Strips Glued into Slitsrdquo inFRPRCS-6 pp 205ndash214 World Scientific Singapore 2003

[18] W T Jung Flexural Behavior of Reinforced Concrete BeamsStrengthened with NSM CFRP Reinforcements Considering theEquivalent Section [PhD thesis] Myongji University SeoulKorea 2009

[19] J S Park W T Jung Y H Park and C Y ldquoThe analysisfor reinforced concrete beams strengthened with externallyunbonded prestressed CFRP platesrdquo Journal of the Korea Societyof Civil Engineers vol 28 no 4A pp 439ndash445 2008

Submit your manuscripts athttpswwwhindawicom

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International Journal of

Biomaterials

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TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

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Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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MetallurgyJournal of

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4 International Journal of Polymer Science

Table 3 Summary of experimental results

Yielding MaximumFailure mode 119889119906119889119910119872119910

kNmm119875119910kN

119889119910mm 119875119875119910 con 119872119906

kNmm119875119906kN

119889119906mm 119875119875119906 con

Control-27MPa 23006 4382 1152 1 25799 4914 4649 1 a 403SL90-E-0 33448 6371 1382 145 59220 1128 6189 23 b 448SL90-E-20 41528 791 1536 181 62543 11913 5378 242 b 35SL90-E-40 47345 9018 1608 206 62029 11815 3846 24 b 239SL70-E-50 52889 10074 1809 23 62606 11925 3848 243 b c 213SL83-E-40 49009 9335 155 213 67032 12768 4304 26 b 278SL77-E-40 48269 9194 1783 21 67872 12928 4637 263 c 26SL70-E-40 48878 931 1799 212 60344 11494 4509 234 c 251a flexural failure b rupture of CFRP tendon c increased cracking of anchor plate

Anchorage plate

CFRP tendon

(a)

Prestressing system

(b)

Filler

(c)

Figure 4 Concept of the new prestressing system developed in this study

Making groove CFRP tendon Anchorage plate

Anchoring by nut

Prestressing system

Prestressing

Removing prestressing system Filling amp curing filler

Figure 5 Application of the new prestressing system

after having installed the hydraulic cylinder as shown inFigure 4(b)Thereafter the anchored end of the CFRP tendonis nut-fastened and prestressing is completed by removing thepressure of the hydraulic cylinder Finally the anchorage isdismantled before filling the groove with the filler and curingthe filler (Figure 4(c))

24 Loading and Measurement Methods All the specimenswere subjected to 4-point bending tests up to failure bymeansof a UTM (Universal Testing Machine) with capacity of

980 kNThe loading was applied under displacement controlat speed of 002mmsec until the first 10mmand005mmsecfrom 10mm until failure The test data were recorded by astatic data logger and a computer at intervals of 1 secondElectrical resistance strain gauges were fixed at mid-span and1198714 to measure the strain of steel reinforcements

3 Experimental Results31 Failure Modes and Strengthening Performances Table 3arranges the experimental results

International Journal of Polymer Science 5

Figure 6 Rupture of CFRP tendon (SL90-E-40)

Figure 7 Cracking of anchor plate (SL70-E-40)

Themoment load anddeflection are represented for eachrebar yielding and maximum load PP_con the load ratioof strengthened specimen to the nonstrengthened specimen(CONTROL) indicates the strengthening effect 119889119906119889119910 thedeflection ratio of maximum to yielding shows the ductil-ity of specimen The control specimen exhibited commonflexure failure occurring through compressive failure of theupper concrete after yielding of the reinforcement Besidesthe prestressed NSM specimens experienced two types offailure mode by rupture of the CFRP tendon after yielding ofthe steel reinforcement (SL90 SL83 Figure 6) and by increaseof the cracks around the anchor plate (SL77 SL70 Figure 7)

32 Strengthening Performance Figure 8 plots the load-deflection curves according to the level of prestressThe crackload and yield load are seen to increase with higher level ofprestress Since the rupture of the CFRP tendon determinesthe member performance similar maximum load can beobserved regardless of the level of prestress and the ductilityappears to reduce In view of the strengthening performancewith respect to the level of prestress the yield load and themaximum load are seen to increase respectively by 45 to130 and by 113 to 143 compared to the control specimen

Figure 9 compares the load-deflection curves accordingto the length of strengthening Since all the consideredspecimens were prestressed up to 40 of the tensile strengthof the CFRP tendon similar crack load yield load andmaximum load can be observedThe ductility tends to reducewith reference to specimen SL83 and can be attributed to

Deflection (mm)0 20 40 60 80

Load

(kN

)

0

20

40

60

80

100

120

140

SL90-E-0SL90-E-20

SL90-E-40SL70-E-50

Control 27－Ｊ

Figure 8 Experimental load-deflection curves

Deflection (mm)0 20 40 60 80

Load

(kN

)

0

20

40

60

80

100

120

140

SL90-E-40SL83-E-40

SL77-E-40SL70-E-40

Control-27－Ｊ

Figure 9 Experimental load-deflection curves

the occurrence of cracks around the anchor plate If thelocation of the anchor plate falls outside the effective depth 119889119904and the length of strengthening shortens the cracks increasearound the anchor plate after yielding of the tensile steeland appears to lower the maximum load since the anchorbecomes insufficient for the rupture of the CFRP tendon

4 Analytical and Experimental Results

41 Section Analysis of Specimens Reinforced by PrestressedNSMR Numerous researchers proposed bond failure mod-els to predict the behaviour of the specimens reinforced byNSMR [16ndash18] However for the prestressed NSMR withanchorage it is impossible to predict the behaviour by sectionanalysis without a complex bond failure model since rupture

6 International Journal of Polymer Science

b

h

c

Initial prestressing

PrestressedNSM

NAdf

ds

sf3

t

f2 f1

fe = f1 + f2 + f3

s

c

fs

ffe

ft

fc

fs

ds

(a)

PrestressedNSM

b

h

c

NA

Initial prestressing

dfds

s

f3 f2f1

fe = f1 + f2 + f3

s

c

fs

ffe

fc

fs

ds

(b)

b

h

cNA

Initial prestressing

PrestressedNSM

df

ds

s

f3 f2 f1

fe = f1 + f2 + f3

s

c

fs

ffe

fc

fs

ds

(c)

Figure 10 Load-deflection curves per analysis stage

of the CFRP tendon occurs when reaching the maximumperformance of the material

Accordingly this study conducts section analysis usingthe strain compatibility and force equilibrium conditions forfurther comparison with the experimental behaviour of thespecimens strengthened by prestressed NSMRThemoment-curvature distribution of the normal concrete specimens canbe subdivided into three stages limited by the initiation ofcracking and the yielding of steel Therefore section analysisis also conducted by distinguishing the working moment bymeans of the load for the stages before cracking after crackingand before yielding of steel and after yielding of steel [11 19]

The calculation at each stage uses the equilibrium conditionsof the forces and moments Figure 10 depicts the distributionof the strain and stress at each stage

(a) Precracking stage is as follows 0 le 119872119886 le 11987211988811990312119891119888119887119888 + 119860

10158401199041198911015840119904 minus 12 (ℎ minus 119888) 119891119888119905119887 minus 119860 119904119891119904 minus 119860119891119891119891119890 = 0

119872119886= 13119891119888119905119887ℎ (ℎ minus 119888) + 119860 119904119891119904 (119889119904 minus

13119888)

+ 119860119891119891119891119890 (119889119891 minus 13119888) minus 11986010158401199041198911015840119904 (13119888 minus 119889

1015840119904)

(1)

International Journal of Polymer Science 7

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

(a) SL90-E-0

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

(b) SL90-E-20

0

20

40

60

80

100

120

140

0 20 40 60 80Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

FRP rupture

(c) SL90-E-40

Deflection (mm)

Load

(kN

)

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

ExperimentalAnalytical

(d) SL70-E-50

Figure 11 Comparison of experimental and analytical load-deflection curves

(b) Preyielding stage is as follows119872119888119903 le 119872119886 le 11987211991012057211205731119891119888119896119887119888 + 11986010158401199041198911015840119904 minus 119860 119904119891119904 minus 119860119891119891119891119890 = 0119872119886= 119860 119904119891119904 (119889119904 minus 121205731119888) + 119860119891119891119891119890 (119889119891 minus

121205731119888)

minus 11986010158401199041198911015840119904 (121205731119888 minus 1198891015840119904)

(2)

(c) Postyielding stage is as follows119872119910 le 119872119886 le 11987211990612057211205731119891119888119896119887119888 + 11986010158401199041198911015840119904 minus 119860 119904 [119891119910 + 1198641015840119904 (120576119904 minus 120576119910)] minus 119860119891119891119891119890= 0119872119886= 119860 119904 [119891119910 + 1198641015840119904 (120576119904 minus 120576119910)] (119889119904 minus 121205731119888)

+ 119860119891119891119891119890 (119889119891 minus 121205731119888) minus 11986010158401199041198911015840119904 (121205731119888 minus 119889

1015840119904)

(3)

42 Calculation Process The calculation determines thedeflection the strain of each material the loads and theposition of the neutral axis by the strain compatibility con-dition while increasing the strain of steel by the constitutiveequations of each material and by the equilibrium of theinternal forces The final failure mode is decided to be thecompressive failure of concrete if the compressive strain ofthe concrete at the top exceeds 0003 or the rupture of theCFRP tendon when exceeding the rupture strain of CFRP

43 Comparison of Analytical and Experimental Results Fig-ures 11 and 12 compare the analytical and experimental resultswith respect to the level of prestressThe analytical predictionof the load-deflection relation is seen to be in good agreementwith the experimental results for the specimens strengthenedby NSMR with prestress levels up to 0 20 40 and50 In particular the maximum load of the specimens withprestress levels of 20 40 and 50 is predicted within anerror running between 4 and 6 Besides the maximumload of the specimen with 0 of prestress is predicted with

8 International Journal of Polymer Science

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(a) SL90-E-0

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(b) SL90-E-20

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(c) SL90-E-40

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(d) SL70-E-50

Figure 12 Comparison of experimental and analytical load-strain curves

an error between 6 and 8 This slightly larger error is dueto the occurrence of local failure at the bottom concrete underthe loaded point (Figure 12(a))

5 Conclusions

This study examined the flexural behaviour of specimensstrengthened by prestressed NSM CFRP tendon The follow-ing conclusions can be drawn

(1) The crack and yield loads increased with higherlevel of prestress but the ductility tended to reduceThe specimens in which failure occurred throughthe rupture of the CFRP tendon showed similarmaximum load

(2) The analysis of the failure mode with respect tothe length of strengthening showed that the failurepattern and cracking pattern varied according to theposition of the anchor plate Flexural failure could be

induced by installing the anchor plate closest to thesupport The experimental results revealed that theanchor plate should be installed within the effectivedepth119889119904 tominimize the occurrence of shear-induceddiagonal cracksThe test results also indicated that thelength ratio of strengthening should be larger than83 to prevent the occurrence of bond failure at theend of the reinforcement

(3) The comparison of the analytical and experimentalresults showed that the section analysis could predictthe maximum load of the specimens strengthened byprestressed NSMR within an error between 4 and6

Conflicts of Interest

The authors declare that they have no conflicts of interest

International Journal of Polymer Science 9

Acknowledgments

This research was supported by a grant from ldquoa StrategicResearch Project funded by the Korea Institute of CivilEngineering and Building Technologyrdquo and ldquoUpgradingTechnology of Prestressed NSM Reinforcement System withCFRP Tendonrdquo

References

[1] M Rezazadeh H Ramezansefat and J Barros ldquoNSM CFRPprestressing techniques with strengthening potential for simul-taneously enhancing load capacity and ductility performancerdquoJournal of Composites for Construction vol 20 no 5 Article ID04016029 2016

[2] W T Jung J S Park and Y H Park ldquoAn experimental study onapplication of new prestressing system for NSM strengtheningtechniquerdquo inProceedings of the 9th International Symposium onFiber Reinforced Polymer Reinforcement for Reinforced ConcreteStructures (FRPRCSrsquo09) 2009

[3] W-T Jung J-S Park and S-H Kim ldquoA study on the behav-ior characteristics of curved FRP-concrete composite panelrdquoAdvanced Materials Research vol 557-559 pp 375ndash380 2012

[4] J S Park Y H Park I J Kwak W T Jung and S Y ChoildquoA Study on FRP Cable System for Cable Stayed Bridgerdquo RampDReport 08 Super-Long Span Bridge C02-01 Korea Institute ofConstruction Technology 2011

[5] W Jung J Park J Kang and M Keum ldquoFlexural behaviorof concrete beam strengthened by near-surface mounted cfrpreinforcement using equivalent section modelrdquo Advances inMaterials Science and Engineering vol 2017 pp 1ndash16 2017

[6] R EI-Hacha ldquoEffectiveness of near surface mounted frp rein-forcement for flexural strengthening of reinforced concretebeamsrdquo in Proceedings of the 4th International Conferenceon Advanced Composite Materials in Bridges and StructuresAlberta Canada 2004

[7] L De Lorenzis and J G Teng ldquoNear-surface mounted FRPreinforcement an emerging technique for strengthening struc-turesrdquoComposites Part B Engineering vol 38 no 2 pp 119ndash1432007

[8] H Nordin and B Taljsten ldquoConcrete beams strengthened withprestressed near surface mounted CFRPrdquo Journal of Compositesfor Construction vol 10 no 1 pp 60ndash68 2006

[9] W T Jung Y H Park and J S Park ldquoA study on the flexuralbehavior of reinforced concrete beams strengthened with NSMprestressed CFRP reinforcementsrdquo in Proceedings of the 8thInternational Symposium on FRP Reinforcement for ConcreteStructures (FRPRCSrsquo08) Patras Greece 2007

[10] H Nordin Flexural Strengthening of Concrete Structures withPrestressed Near Surface Mounted CFRP Rods Lulea Universityof Technology 2003

[11] M A BadawiMonotonic and Fatigue Flexural Behaviour of RCBeams Strengthened with Prestressed NSM CFRP Rods [PhDthesis] University of Waterloo Waterloo Ontario Canada2007

[12] R El-Hacha and K Soudki ldquoPrestressed near-surface mountedfibre reinforced polymer reinforcement for concrete structures- A reviewrdquo Canadian Journal of Civil Engineering vol 40 no11 pp 1127ndash1139 2013

[13] M Badawi and K Soudki ldquoFatigue behavior of RC beamsstrengthened with NSM CFRP rodsrdquo Journal of Composites forConstruction vol 13 no 5 pp 415ndash421 2009

[14] FOudah andR El-Hacha ldquoPerformance of RCbeams strength-ened using prestressed NSM-CFRP strips subjected to fatigueloadingrdquo Journal of Composites for Construction vol 16 no 3pp 300ndash307 2012

[15] KICT ldquoDevelopment of Bridge Strengthening Methods usingPrestressed FRP Compositesrdquo Tech Rep 2015

[16] T Hassan and S Rizkalla ldquoInvestigation of bond in concretestructures strengthened with near surface mounted carbonfiber reinforced polymer stripsrdquo Journal of Composites forConstruction vol 7 no 3 pp 248ndash257 2003

[17] M Blaschko ldquoBond Behavior of Strips Glued into Slitsrdquo inFRPRCS-6 pp 205ndash214 World Scientific Singapore 2003

[18] W T Jung Flexural Behavior of Reinforced Concrete BeamsStrengthened with NSM CFRP Reinforcements Considering theEquivalent Section [PhD thesis] Myongji University SeoulKorea 2009

[19] J S Park W T Jung Y H Park and C Y ldquoThe analysisfor reinforced concrete beams strengthened with externallyunbonded prestressed CFRP platesrdquo Journal of the Korea Societyof Civil Engineers vol 28 no 4A pp 439ndash445 2008

Submit your manuscripts athttpswwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of Polymer Science 5

Figure 6 Rupture of CFRP tendon (SL90-E-40)

Figure 7 Cracking of anchor plate (SL70-E-40)

Themoment load anddeflection are represented for eachrebar yielding and maximum load PP_con the load ratioof strengthened specimen to the nonstrengthened specimen(CONTROL) indicates the strengthening effect 119889119906119889119910 thedeflection ratio of maximum to yielding shows the ductil-ity of specimen The control specimen exhibited commonflexure failure occurring through compressive failure of theupper concrete after yielding of the reinforcement Besidesthe prestressed NSM specimens experienced two types offailure mode by rupture of the CFRP tendon after yielding ofthe steel reinforcement (SL90 SL83 Figure 6) and by increaseof the cracks around the anchor plate (SL77 SL70 Figure 7)

32 Strengthening Performance Figure 8 plots the load-deflection curves according to the level of prestressThe crackload and yield load are seen to increase with higher level ofprestress Since the rupture of the CFRP tendon determinesthe member performance similar maximum load can beobserved regardless of the level of prestress and the ductilityappears to reduce In view of the strengthening performancewith respect to the level of prestress the yield load and themaximum load are seen to increase respectively by 45 to130 and by 113 to 143 compared to the control specimen

Figure 9 compares the load-deflection curves accordingto the length of strengthening Since all the consideredspecimens were prestressed up to 40 of the tensile strengthof the CFRP tendon similar crack load yield load andmaximum load can be observedThe ductility tends to reducewith reference to specimen SL83 and can be attributed to

Deflection (mm)0 20 40 60 80

Load

(kN

)

0

20

40

60

80

100

120

140

SL90-E-0SL90-E-20

SL90-E-40SL70-E-50

Control 27－Ｊ

Figure 8 Experimental load-deflection curves

Deflection (mm)0 20 40 60 80

Load

(kN

)

0

20

40

60

80

100

120

140

SL90-E-40SL83-E-40

SL77-E-40SL70-E-40

Control-27－Ｊ

Figure 9 Experimental load-deflection curves

the occurrence of cracks around the anchor plate If thelocation of the anchor plate falls outside the effective depth 119889119904and the length of strengthening shortens the cracks increasearound the anchor plate after yielding of the tensile steeland appears to lower the maximum load since the anchorbecomes insufficient for the rupture of the CFRP tendon

4 Analytical and Experimental Results

41 Section Analysis of Specimens Reinforced by PrestressedNSMR Numerous researchers proposed bond failure mod-els to predict the behaviour of the specimens reinforced byNSMR [16ndash18] However for the prestressed NSMR withanchorage it is impossible to predict the behaviour by sectionanalysis without a complex bond failure model since rupture

6 International Journal of Polymer Science

b

h

c

Initial prestressing

PrestressedNSM

NAdf

ds

sf3

t

f2 f1

fe = f1 + f2 + f3

s

c

fs

ffe

ft

fc

fs

ds

(a)

PrestressedNSM

b

h

c

NA

Initial prestressing

dfds

s

f3 f2f1

fe = f1 + f2 + f3

s

c

fs

ffe

fc

fs

ds

(b)

b

h

cNA

Initial prestressing

PrestressedNSM

df

ds

s

f3 f2 f1

fe = f1 + f2 + f3

s

c

fs

ffe

fc

fs

ds

(c)

Figure 10 Load-deflection curves per analysis stage

of the CFRP tendon occurs when reaching the maximumperformance of the material

Accordingly this study conducts section analysis usingthe strain compatibility and force equilibrium conditions forfurther comparison with the experimental behaviour of thespecimens strengthened by prestressed NSMRThemoment-curvature distribution of the normal concrete specimens canbe subdivided into three stages limited by the initiation ofcracking and the yielding of steel Therefore section analysisis also conducted by distinguishing the working moment bymeans of the load for the stages before cracking after crackingand before yielding of steel and after yielding of steel [11 19]

The calculation at each stage uses the equilibrium conditionsof the forces and moments Figure 10 depicts the distributionof the strain and stress at each stage

(a) Precracking stage is as follows 0 le 119872119886 le 11987211988811990312119891119888119887119888 + 119860

10158401199041198911015840119904 minus 12 (ℎ minus 119888) 119891119888119905119887 minus 119860 119904119891119904 minus 119860119891119891119891119890 = 0

119872119886= 13119891119888119905119887ℎ (ℎ minus 119888) + 119860 119904119891119904 (119889119904 minus

13119888)

+ 119860119891119891119891119890 (119889119891 minus 13119888) minus 11986010158401199041198911015840119904 (13119888 minus 119889

1015840119904)

(1)

International Journal of Polymer Science 7

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

(a) SL90-E-0

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

(b) SL90-E-20

0

20

40

60

80

100

120

140

0 20 40 60 80Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

FRP rupture

(c) SL90-E-40

Deflection (mm)

Load

(kN

)

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

ExperimentalAnalytical

(d) SL70-E-50

Figure 11 Comparison of experimental and analytical load-deflection curves

(b) Preyielding stage is as follows119872119888119903 le 119872119886 le 11987211991012057211205731119891119888119896119887119888 + 11986010158401199041198911015840119904 minus 119860 119904119891119904 minus 119860119891119891119891119890 = 0119872119886= 119860 119904119891119904 (119889119904 minus 121205731119888) + 119860119891119891119891119890 (119889119891 minus

121205731119888)

minus 11986010158401199041198911015840119904 (121205731119888 minus 1198891015840119904)

(2)

(c) Postyielding stage is as follows119872119910 le 119872119886 le 11987211990612057211205731119891119888119896119887119888 + 11986010158401199041198911015840119904 minus 119860 119904 [119891119910 + 1198641015840119904 (120576119904 minus 120576119910)] minus 119860119891119891119891119890= 0119872119886= 119860 119904 [119891119910 + 1198641015840119904 (120576119904 minus 120576119910)] (119889119904 minus 121205731119888)

+ 119860119891119891119891119890 (119889119891 minus 121205731119888) minus 11986010158401199041198911015840119904 (121205731119888 minus 119889

1015840119904)

(3)

42 Calculation Process The calculation determines thedeflection the strain of each material the loads and theposition of the neutral axis by the strain compatibility con-dition while increasing the strain of steel by the constitutiveequations of each material and by the equilibrium of theinternal forces The final failure mode is decided to be thecompressive failure of concrete if the compressive strain ofthe concrete at the top exceeds 0003 or the rupture of theCFRP tendon when exceeding the rupture strain of CFRP

43 Comparison of Analytical and Experimental Results Fig-ures 11 and 12 compare the analytical and experimental resultswith respect to the level of prestressThe analytical predictionof the load-deflection relation is seen to be in good agreementwith the experimental results for the specimens strengthenedby NSMR with prestress levels up to 0 20 40 and50 In particular the maximum load of the specimens withprestress levels of 20 40 and 50 is predicted within anerror running between 4 and 6 Besides the maximumload of the specimen with 0 of prestress is predicted with

8 International Journal of Polymer Science

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(a) SL90-E-0

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(b) SL90-E-20

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(c) SL90-E-40

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(d) SL70-E-50

Figure 12 Comparison of experimental and analytical load-strain curves

an error between 6 and 8 This slightly larger error is dueto the occurrence of local failure at the bottom concrete underthe loaded point (Figure 12(a))

5 Conclusions

This study examined the flexural behaviour of specimensstrengthened by prestressed NSM CFRP tendon The follow-ing conclusions can be drawn

(1) The crack and yield loads increased with higherlevel of prestress but the ductility tended to reduceThe specimens in which failure occurred throughthe rupture of the CFRP tendon showed similarmaximum load

(2) The analysis of the failure mode with respect tothe length of strengthening showed that the failurepattern and cracking pattern varied according to theposition of the anchor plate Flexural failure could be

induced by installing the anchor plate closest to thesupport The experimental results revealed that theanchor plate should be installed within the effectivedepth119889119904 tominimize the occurrence of shear-induceddiagonal cracksThe test results also indicated that thelength ratio of strengthening should be larger than83 to prevent the occurrence of bond failure at theend of the reinforcement

(3) The comparison of the analytical and experimentalresults showed that the section analysis could predictthe maximum load of the specimens strengthened byprestressed NSMR within an error between 4 and6

Conflicts of Interest

The authors declare that they have no conflicts of interest

International Journal of Polymer Science 9

Acknowledgments

This research was supported by a grant from ldquoa StrategicResearch Project funded by the Korea Institute of CivilEngineering and Building Technologyrdquo and ldquoUpgradingTechnology of Prestressed NSM Reinforcement System withCFRP Tendonrdquo

References

[1] M Rezazadeh H Ramezansefat and J Barros ldquoNSM CFRPprestressing techniques with strengthening potential for simul-taneously enhancing load capacity and ductility performancerdquoJournal of Composites for Construction vol 20 no 5 Article ID04016029 2016

[2] W T Jung J S Park and Y H Park ldquoAn experimental study onapplication of new prestressing system for NSM strengtheningtechniquerdquo inProceedings of the 9th International Symposium onFiber Reinforced Polymer Reinforcement for Reinforced ConcreteStructures (FRPRCSrsquo09) 2009

[3] W-T Jung J-S Park and S-H Kim ldquoA study on the behav-ior characteristics of curved FRP-concrete composite panelrdquoAdvanced Materials Research vol 557-559 pp 375ndash380 2012

[4] J S Park Y H Park I J Kwak W T Jung and S Y ChoildquoA Study on FRP Cable System for Cable Stayed Bridgerdquo RampDReport 08 Super-Long Span Bridge C02-01 Korea Institute ofConstruction Technology 2011

[5] W Jung J Park J Kang and M Keum ldquoFlexural behaviorof concrete beam strengthened by near-surface mounted cfrpreinforcement using equivalent section modelrdquo Advances inMaterials Science and Engineering vol 2017 pp 1ndash16 2017

[6] R EI-Hacha ldquoEffectiveness of near surface mounted frp rein-forcement for flexural strengthening of reinforced concretebeamsrdquo in Proceedings of the 4th International Conferenceon Advanced Composite Materials in Bridges and StructuresAlberta Canada 2004

[7] L De Lorenzis and J G Teng ldquoNear-surface mounted FRPreinforcement an emerging technique for strengthening struc-turesrdquoComposites Part B Engineering vol 38 no 2 pp 119ndash1432007

[8] H Nordin and B Taljsten ldquoConcrete beams strengthened withprestressed near surface mounted CFRPrdquo Journal of Compositesfor Construction vol 10 no 1 pp 60ndash68 2006

[9] W T Jung Y H Park and J S Park ldquoA study on the flexuralbehavior of reinforced concrete beams strengthened with NSMprestressed CFRP reinforcementsrdquo in Proceedings of the 8thInternational Symposium on FRP Reinforcement for ConcreteStructures (FRPRCSrsquo08) Patras Greece 2007

[10] H Nordin Flexural Strengthening of Concrete Structures withPrestressed Near Surface Mounted CFRP Rods Lulea Universityof Technology 2003

[11] M A BadawiMonotonic and Fatigue Flexural Behaviour of RCBeams Strengthened with Prestressed NSM CFRP Rods [PhDthesis] University of Waterloo Waterloo Ontario Canada2007

[12] R El-Hacha and K Soudki ldquoPrestressed near-surface mountedfibre reinforced polymer reinforcement for concrete structures- A reviewrdquo Canadian Journal of Civil Engineering vol 40 no11 pp 1127ndash1139 2013

[13] M Badawi and K Soudki ldquoFatigue behavior of RC beamsstrengthened with NSM CFRP rodsrdquo Journal of Composites forConstruction vol 13 no 5 pp 415ndash421 2009

[14] FOudah andR El-Hacha ldquoPerformance of RCbeams strength-ened using prestressed NSM-CFRP strips subjected to fatigueloadingrdquo Journal of Composites for Construction vol 16 no 3pp 300ndash307 2012

[15] KICT ldquoDevelopment of Bridge Strengthening Methods usingPrestressed FRP Compositesrdquo Tech Rep 2015

[16] T Hassan and S Rizkalla ldquoInvestigation of bond in concretestructures strengthened with near surface mounted carbonfiber reinforced polymer stripsrdquo Journal of Composites forConstruction vol 7 no 3 pp 248ndash257 2003

[17] M Blaschko ldquoBond Behavior of Strips Glued into Slitsrdquo inFRPRCS-6 pp 205ndash214 World Scientific Singapore 2003

[18] W T Jung Flexural Behavior of Reinforced Concrete BeamsStrengthened with NSM CFRP Reinforcements Considering theEquivalent Section [PhD thesis] Myongji University SeoulKorea 2009

[19] J S Park W T Jung Y H Park and C Y ldquoThe analysisfor reinforced concrete beams strengthened with externallyunbonded prestressed CFRP platesrdquo Journal of the Korea Societyof Civil Engineers vol 28 no 4A pp 439ndash445 2008

Submit your manuscripts athttpswwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

6 International Journal of Polymer Science

b

h

c

Initial prestressing

PrestressedNSM

NAdf

ds

sf3

t

f2 f1

fe = f1 + f2 + f3

s

c

fs

ffe

ft

fc

fs

ds

(a)

PrestressedNSM

b

h

c

NA

Initial prestressing

dfds

s

f3 f2f1

fe = f1 + f2 + f3

s

c

fs

ffe

fc

fs

ds

(b)

b

h

cNA

Initial prestressing

PrestressedNSM

df

ds

s

f3 f2 f1

fe = f1 + f2 + f3

s

c

fs

ffe

fc

fs

ds

(c)

Figure 10 Load-deflection curves per analysis stage

of the CFRP tendon occurs when reaching the maximumperformance of the material

Accordingly this study conducts section analysis usingthe strain compatibility and force equilibrium conditions forfurther comparison with the experimental behaviour of thespecimens strengthened by prestressed NSMRThemoment-curvature distribution of the normal concrete specimens canbe subdivided into three stages limited by the initiation ofcracking and the yielding of steel Therefore section analysisis also conducted by distinguishing the working moment bymeans of the load for the stages before cracking after crackingand before yielding of steel and after yielding of steel [11 19]

The calculation at each stage uses the equilibrium conditionsof the forces and moments Figure 10 depicts the distributionof the strain and stress at each stage

(a) Precracking stage is as follows 0 le 119872119886 le 11987211988811990312119891119888119887119888 + 119860

10158401199041198911015840119904 minus 12 (ℎ minus 119888) 119891119888119905119887 minus 119860 119904119891119904 minus 119860119891119891119891119890 = 0

119872119886= 13119891119888119905119887ℎ (ℎ minus 119888) + 119860 119904119891119904 (119889119904 minus

13119888)

+ 119860119891119891119891119890 (119889119891 minus 13119888) minus 11986010158401199041198911015840119904 (13119888 minus 119889

1015840119904)

(1)

International Journal of Polymer Science 7

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

(a) SL90-E-0

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

(b) SL90-E-20

0

20

40

60

80

100

120

140

0 20 40 60 80Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

FRP rupture

(c) SL90-E-40

Deflection (mm)

Load

(kN

)

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

ExperimentalAnalytical

(d) SL70-E-50

Figure 11 Comparison of experimental and analytical load-deflection curves

(b) Preyielding stage is as follows119872119888119903 le 119872119886 le 11987211991012057211205731119891119888119896119887119888 + 11986010158401199041198911015840119904 minus 119860 119904119891119904 minus 119860119891119891119891119890 = 0119872119886= 119860 119904119891119904 (119889119904 minus 121205731119888) + 119860119891119891119891119890 (119889119891 minus

121205731119888)

minus 11986010158401199041198911015840119904 (121205731119888 minus 1198891015840119904)

(2)

(c) Postyielding stage is as follows119872119910 le 119872119886 le 11987211990612057211205731119891119888119896119887119888 + 11986010158401199041198911015840119904 minus 119860 119904 [119891119910 + 1198641015840119904 (120576119904 minus 120576119910)] minus 119860119891119891119891119890= 0119872119886= 119860 119904 [119891119910 + 1198641015840119904 (120576119904 minus 120576119910)] (119889119904 minus 121205731119888)

+ 119860119891119891119891119890 (119889119891 minus 121205731119888) minus 11986010158401199041198911015840119904 (121205731119888 minus 119889

1015840119904)

(3)

42 Calculation Process The calculation determines thedeflection the strain of each material the loads and theposition of the neutral axis by the strain compatibility con-dition while increasing the strain of steel by the constitutiveequations of each material and by the equilibrium of theinternal forces The final failure mode is decided to be thecompressive failure of concrete if the compressive strain ofthe concrete at the top exceeds 0003 or the rupture of theCFRP tendon when exceeding the rupture strain of CFRP

43 Comparison of Analytical and Experimental Results Fig-ures 11 and 12 compare the analytical and experimental resultswith respect to the level of prestressThe analytical predictionof the load-deflection relation is seen to be in good agreementwith the experimental results for the specimens strengthenedby NSMR with prestress levels up to 0 20 40 and50 In particular the maximum load of the specimens withprestress levels of 20 40 and 50 is predicted within anerror running between 4 and 6 Besides the maximumload of the specimen with 0 of prestress is predicted with

8 International Journal of Polymer Science

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(a) SL90-E-0

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(b) SL90-E-20

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(c) SL90-E-40

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(d) SL70-E-50

Figure 12 Comparison of experimental and analytical load-strain curves

an error between 6 and 8 This slightly larger error is dueto the occurrence of local failure at the bottom concrete underthe loaded point (Figure 12(a))

5 Conclusions

This study examined the flexural behaviour of specimensstrengthened by prestressed NSM CFRP tendon The follow-ing conclusions can be drawn

(1) The crack and yield loads increased with higherlevel of prestress but the ductility tended to reduceThe specimens in which failure occurred throughthe rupture of the CFRP tendon showed similarmaximum load

(2) The analysis of the failure mode with respect tothe length of strengthening showed that the failurepattern and cracking pattern varied according to theposition of the anchor plate Flexural failure could be

induced by installing the anchor plate closest to thesupport The experimental results revealed that theanchor plate should be installed within the effectivedepth119889119904 tominimize the occurrence of shear-induceddiagonal cracksThe test results also indicated that thelength ratio of strengthening should be larger than83 to prevent the occurrence of bond failure at theend of the reinforcement

(3) The comparison of the analytical and experimentalresults showed that the section analysis could predictthe maximum load of the specimens strengthened byprestressed NSMR within an error between 4 and6

Conflicts of Interest

The authors declare that they have no conflicts of interest

International Journal of Polymer Science 9

Acknowledgments

This research was supported by a grant from ldquoa StrategicResearch Project funded by the Korea Institute of CivilEngineering and Building Technologyrdquo and ldquoUpgradingTechnology of Prestressed NSM Reinforcement System withCFRP Tendonrdquo

References

[1] M Rezazadeh H Ramezansefat and J Barros ldquoNSM CFRPprestressing techniques with strengthening potential for simul-taneously enhancing load capacity and ductility performancerdquoJournal of Composites for Construction vol 20 no 5 Article ID04016029 2016

[2] W T Jung J S Park and Y H Park ldquoAn experimental study onapplication of new prestressing system for NSM strengtheningtechniquerdquo inProceedings of the 9th International Symposium onFiber Reinforced Polymer Reinforcement for Reinforced ConcreteStructures (FRPRCSrsquo09) 2009

[3] W-T Jung J-S Park and S-H Kim ldquoA study on the behav-ior characteristics of curved FRP-concrete composite panelrdquoAdvanced Materials Research vol 557-559 pp 375ndash380 2012

[4] J S Park Y H Park I J Kwak W T Jung and S Y ChoildquoA Study on FRP Cable System for Cable Stayed Bridgerdquo RampDReport 08 Super-Long Span Bridge C02-01 Korea Institute ofConstruction Technology 2011

[5] W Jung J Park J Kang and M Keum ldquoFlexural behaviorof concrete beam strengthened by near-surface mounted cfrpreinforcement using equivalent section modelrdquo Advances inMaterials Science and Engineering vol 2017 pp 1ndash16 2017

[6] R EI-Hacha ldquoEffectiveness of near surface mounted frp rein-forcement for flexural strengthening of reinforced concretebeamsrdquo in Proceedings of the 4th International Conferenceon Advanced Composite Materials in Bridges and StructuresAlberta Canada 2004

[7] L De Lorenzis and J G Teng ldquoNear-surface mounted FRPreinforcement an emerging technique for strengthening struc-turesrdquoComposites Part B Engineering vol 38 no 2 pp 119ndash1432007

[8] H Nordin and B Taljsten ldquoConcrete beams strengthened withprestressed near surface mounted CFRPrdquo Journal of Compositesfor Construction vol 10 no 1 pp 60ndash68 2006

[9] W T Jung Y H Park and J S Park ldquoA study on the flexuralbehavior of reinforced concrete beams strengthened with NSMprestressed CFRP reinforcementsrdquo in Proceedings of the 8thInternational Symposium on FRP Reinforcement for ConcreteStructures (FRPRCSrsquo08) Patras Greece 2007

[10] H Nordin Flexural Strengthening of Concrete Structures withPrestressed Near Surface Mounted CFRP Rods Lulea Universityof Technology 2003

[11] M A BadawiMonotonic and Fatigue Flexural Behaviour of RCBeams Strengthened with Prestressed NSM CFRP Rods [PhDthesis] University of Waterloo Waterloo Ontario Canada2007

[12] R El-Hacha and K Soudki ldquoPrestressed near-surface mountedfibre reinforced polymer reinforcement for concrete structures- A reviewrdquo Canadian Journal of Civil Engineering vol 40 no11 pp 1127ndash1139 2013

[13] M Badawi and K Soudki ldquoFatigue behavior of RC beamsstrengthened with NSM CFRP rodsrdquo Journal of Composites forConstruction vol 13 no 5 pp 415ndash421 2009

[14] FOudah andR El-Hacha ldquoPerformance of RCbeams strength-ened using prestressed NSM-CFRP strips subjected to fatigueloadingrdquo Journal of Composites for Construction vol 16 no 3pp 300ndash307 2012

[15] KICT ldquoDevelopment of Bridge Strengthening Methods usingPrestressed FRP Compositesrdquo Tech Rep 2015

[16] T Hassan and S Rizkalla ldquoInvestigation of bond in concretestructures strengthened with near surface mounted carbonfiber reinforced polymer stripsrdquo Journal of Composites forConstruction vol 7 no 3 pp 248ndash257 2003

[17] M Blaschko ldquoBond Behavior of Strips Glued into Slitsrdquo inFRPRCS-6 pp 205ndash214 World Scientific Singapore 2003

[18] W T Jung Flexural Behavior of Reinforced Concrete BeamsStrengthened with NSM CFRP Reinforcements Considering theEquivalent Section [PhD thesis] Myongji University SeoulKorea 2009

[19] J S Park W T Jung Y H Park and C Y ldquoThe analysisfor reinforced concrete beams strengthened with externallyunbonded prestressed CFRP platesrdquo Journal of the Korea Societyof Civil Engineers vol 28 no 4A pp 439ndash445 2008

Submit your manuscripts athttpswwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of Polymer Science 7

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

(a) SL90-E-0

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

(b) SL90-E-20

0

20

40

60

80

100

120

140

0 20 40 60 80Deflection (mm)

Load

(kN

)

ExperimentalAnalytical

FRP rupture

(c) SL90-E-40

Deflection (mm)

Load

(kN

)

0

20

40

60

80

100

120

140

0 20 40 60 80

FRP rupture

ExperimentalAnalytical

(d) SL70-E-50

Figure 11 Comparison of experimental and analytical load-deflection curves

(b) Preyielding stage is as follows119872119888119903 le 119872119886 le 11987211991012057211205731119891119888119896119887119888 + 11986010158401199041198911015840119904 minus 119860 119904119891119904 minus 119860119891119891119891119890 = 0119872119886= 119860 119904119891119904 (119889119904 minus 121205731119888) + 119860119891119891119891119890 (119889119891 minus

121205731119888)

minus 11986010158401199041198911015840119904 (121205731119888 minus 1198891015840119904)

(2)

(c) Postyielding stage is as follows119872119910 le 119872119886 le 11987211990612057211205731119891119888119896119887119888 + 11986010158401199041198911015840119904 minus 119860 119904 [119891119910 + 1198641015840119904 (120576119904 minus 120576119910)] minus 119860119891119891119891119890= 0119872119886= 119860 119904 [119891119910 + 1198641015840119904 (120576119904 minus 120576119910)] (119889119904 minus 121205731119888)

+ 119860119891119891119891119890 (119889119891 minus 121205731119888) minus 11986010158401199041198911015840119904 (121205731119888 minus 119889

1015840119904)

(3)

42 Calculation Process The calculation determines thedeflection the strain of each material the loads and theposition of the neutral axis by the strain compatibility con-dition while increasing the strain of steel by the constitutiveequations of each material and by the equilibrium of theinternal forces The final failure mode is decided to be thecompressive failure of concrete if the compressive strain ofthe concrete at the top exceeds 0003 or the rupture of theCFRP tendon when exceeding the rupture strain of CFRP

43 Comparison of Analytical and Experimental Results Fig-ures 11 and 12 compare the analytical and experimental resultswith respect to the level of prestressThe analytical predictionof the load-deflection relation is seen to be in good agreementwith the experimental results for the specimens strengthenedby NSMR with prestress levels up to 0 20 40 and50 In particular the maximum load of the specimens withprestress levels of 20 40 and 50 is predicted within anerror running between 4 and 6 Besides the maximumload of the specimen with 0 of prestress is predicted with

8 International Journal of Polymer Science

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(a) SL90-E-0

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(b) SL90-E-20

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(c) SL90-E-40

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(d) SL70-E-50

Figure 12 Comparison of experimental and analytical load-strain curves

an error between 6 and 8 This slightly larger error is dueto the occurrence of local failure at the bottom concrete underthe loaded point (Figure 12(a))

5 Conclusions

This study examined the flexural behaviour of specimensstrengthened by prestressed NSM CFRP tendon The follow-ing conclusions can be drawn

(1) The crack and yield loads increased with higherlevel of prestress but the ductility tended to reduceThe specimens in which failure occurred throughthe rupture of the CFRP tendon showed similarmaximum load

(2) The analysis of the failure mode with respect tothe length of strengthening showed that the failurepattern and cracking pattern varied according to theposition of the anchor plate Flexural failure could be

induced by installing the anchor plate closest to thesupport The experimental results revealed that theanchor plate should be installed within the effectivedepth119889119904 tominimize the occurrence of shear-induceddiagonal cracksThe test results also indicated that thelength ratio of strengthening should be larger than83 to prevent the occurrence of bond failure at theend of the reinforcement

(3) The comparison of the analytical and experimentalresults showed that the section analysis could predictthe maximum load of the specimens strengthened byprestressed NSMR within an error between 4 and6

Conflicts of Interest

The authors declare that they have no conflicts of interest

International Journal of Polymer Science 9

Acknowledgments

This research was supported by a grant from ldquoa StrategicResearch Project funded by the Korea Institute of CivilEngineering and Building Technologyrdquo and ldquoUpgradingTechnology of Prestressed NSM Reinforcement System withCFRP Tendonrdquo

References

[1] M Rezazadeh H Ramezansefat and J Barros ldquoNSM CFRPprestressing techniques with strengthening potential for simul-taneously enhancing load capacity and ductility performancerdquoJournal of Composites for Construction vol 20 no 5 Article ID04016029 2016

[2] W T Jung J S Park and Y H Park ldquoAn experimental study onapplication of new prestressing system for NSM strengtheningtechniquerdquo inProceedings of the 9th International Symposium onFiber Reinforced Polymer Reinforcement for Reinforced ConcreteStructures (FRPRCSrsquo09) 2009

[3] W-T Jung J-S Park and S-H Kim ldquoA study on the behav-ior characteristics of curved FRP-concrete composite panelrdquoAdvanced Materials Research vol 557-559 pp 375ndash380 2012

[4] J S Park Y H Park I J Kwak W T Jung and S Y ChoildquoA Study on FRP Cable System for Cable Stayed Bridgerdquo RampDReport 08 Super-Long Span Bridge C02-01 Korea Institute ofConstruction Technology 2011

[5] W Jung J Park J Kang and M Keum ldquoFlexural behaviorof concrete beam strengthened by near-surface mounted cfrpreinforcement using equivalent section modelrdquo Advances inMaterials Science and Engineering vol 2017 pp 1ndash16 2017

[6] R EI-Hacha ldquoEffectiveness of near surface mounted frp rein-forcement for flexural strengthening of reinforced concretebeamsrdquo in Proceedings of the 4th International Conferenceon Advanced Composite Materials in Bridges and StructuresAlberta Canada 2004

[7] L De Lorenzis and J G Teng ldquoNear-surface mounted FRPreinforcement an emerging technique for strengthening struc-turesrdquoComposites Part B Engineering vol 38 no 2 pp 119ndash1432007

[8] H Nordin and B Taljsten ldquoConcrete beams strengthened withprestressed near surface mounted CFRPrdquo Journal of Compositesfor Construction vol 10 no 1 pp 60ndash68 2006

[9] W T Jung Y H Park and J S Park ldquoA study on the flexuralbehavior of reinforced concrete beams strengthened with NSMprestressed CFRP reinforcementsrdquo in Proceedings of the 8thInternational Symposium on FRP Reinforcement for ConcreteStructures (FRPRCSrsquo08) Patras Greece 2007

[10] H Nordin Flexural Strengthening of Concrete Structures withPrestressed Near Surface Mounted CFRP Rods Lulea Universityof Technology 2003

[11] M A BadawiMonotonic and Fatigue Flexural Behaviour of RCBeams Strengthened with Prestressed NSM CFRP Rods [PhDthesis] University of Waterloo Waterloo Ontario Canada2007

[12] R El-Hacha and K Soudki ldquoPrestressed near-surface mountedfibre reinforced polymer reinforcement for concrete structures- A reviewrdquo Canadian Journal of Civil Engineering vol 40 no11 pp 1127ndash1139 2013

[13] M Badawi and K Soudki ldquoFatigue behavior of RC beamsstrengthened with NSM CFRP rodsrdquo Journal of Composites forConstruction vol 13 no 5 pp 415ndash421 2009

[14] FOudah andR El-Hacha ldquoPerformance of RCbeams strength-ened using prestressed NSM-CFRP strips subjected to fatigueloadingrdquo Journal of Composites for Construction vol 16 no 3pp 300ndash307 2012

[15] KICT ldquoDevelopment of Bridge Strengthening Methods usingPrestressed FRP Compositesrdquo Tech Rep 2015

[16] T Hassan and S Rizkalla ldquoInvestigation of bond in concretestructures strengthened with near surface mounted carbonfiber reinforced polymer stripsrdquo Journal of Composites forConstruction vol 7 no 3 pp 248ndash257 2003

[17] M Blaschko ldquoBond Behavior of Strips Glued into Slitsrdquo inFRPRCS-6 pp 205ndash214 World Scientific Singapore 2003

[18] W T Jung Flexural Behavior of Reinforced Concrete BeamsStrengthened with NSM CFRP Reinforcements Considering theEquivalent Section [PhD thesis] Myongji University SeoulKorea 2009

[19] J S Park W T Jung Y H Park and C Y ldquoThe analysisfor reinforced concrete beams strengthened with externallyunbonded prestressed CFRP platesrdquo Journal of the Korea Societyof Civil Engineers vol 28 no 4A pp 439ndash445 2008

Submit your manuscripts athttpswwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

8 International Journal of Polymer Science

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(a) SL90-E-0

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(b) SL90-E-20

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(c) SL90-E-40

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000

Load

(kN

)

CFRP strain (lowast10minus6)

ExperimentalAnalytical

(d) SL70-E-50

Figure 12 Comparison of experimental and analytical load-strain curves

an error between 6 and 8 This slightly larger error is dueto the occurrence of local failure at the bottom concrete underthe loaded point (Figure 12(a))

5 Conclusions

This study examined the flexural behaviour of specimensstrengthened by prestressed NSM CFRP tendon The follow-ing conclusions can be drawn

(1) The crack and yield loads increased with higherlevel of prestress but the ductility tended to reduceThe specimens in which failure occurred throughthe rupture of the CFRP tendon showed similarmaximum load

(2) The analysis of the failure mode with respect tothe length of strengthening showed that the failurepattern and cracking pattern varied according to theposition of the anchor plate Flexural failure could be

induced by installing the anchor plate closest to thesupport The experimental results revealed that theanchor plate should be installed within the effectivedepth119889119904 tominimize the occurrence of shear-induceddiagonal cracksThe test results also indicated that thelength ratio of strengthening should be larger than83 to prevent the occurrence of bond failure at theend of the reinforcement

(3) The comparison of the analytical and experimentalresults showed that the section analysis could predictthe maximum load of the specimens strengthened byprestressed NSMR within an error between 4 and6

Conflicts of Interest

The authors declare that they have no conflicts of interest

International Journal of Polymer Science 9

Acknowledgments

This research was supported by a grant from ldquoa StrategicResearch Project funded by the Korea Institute of CivilEngineering and Building Technologyrdquo and ldquoUpgradingTechnology of Prestressed NSM Reinforcement System withCFRP Tendonrdquo

References

[1] M Rezazadeh H Ramezansefat and J Barros ldquoNSM CFRPprestressing techniques with strengthening potential for simul-taneously enhancing load capacity and ductility performancerdquoJournal of Composites for Construction vol 20 no 5 Article ID04016029 2016

[2] W T Jung J S Park and Y H Park ldquoAn experimental study onapplication of new prestressing system for NSM strengtheningtechniquerdquo inProceedings of the 9th International Symposium onFiber Reinforced Polymer Reinforcement for Reinforced ConcreteStructures (FRPRCSrsquo09) 2009

[3] W-T Jung J-S Park and S-H Kim ldquoA study on the behav-ior characteristics of curved FRP-concrete composite panelrdquoAdvanced Materials Research vol 557-559 pp 375ndash380 2012

[4] J S Park Y H Park I J Kwak W T Jung and S Y ChoildquoA Study on FRP Cable System for Cable Stayed Bridgerdquo RampDReport 08 Super-Long Span Bridge C02-01 Korea Institute ofConstruction Technology 2011

[5] W Jung J Park J Kang and M Keum ldquoFlexural behaviorof concrete beam strengthened by near-surface mounted cfrpreinforcement using equivalent section modelrdquo Advances inMaterials Science and Engineering vol 2017 pp 1ndash16 2017

[6] R EI-Hacha ldquoEffectiveness of near surface mounted frp rein-forcement for flexural strengthening of reinforced concretebeamsrdquo in Proceedings of the 4th International Conferenceon Advanced Composite Materials in Bridges and StructuresAlberta Canada 2004

[7] L De Lorenzis and J G Teng ldquoNear-surface mounted FRPreinforcement an emerging technique for strengthening struc-turesrdquoComposites Part B Engineering vol 38 no 2 pp 119ndash1432007

[8] H Nordin and B Taljsten ldquoConcrete beams strengthened withprestressed near surface mounted CFRPrdquo Journal of Compositesfor Construction vol 10 no 1 pp 60ndash68 2006

[9] W T Jung Y H Park and J S Park ldquoA study on the flexuralbehavior of reinforced concrete beams strengthened with NSMprestressed CFRP reinforcementsrdquo in Proceedings of the 8thInternational Symposium on FRP Reinforcement for ConcreteStructures (FRPRCSrsquo08) Patras Greece 2007

[10] H Nordin Flexural Strengthening of Concrete Structures withPrestressed Near Surface Mounted CFRP Rods Lulea Universityof Technology 2003

[11] M A BadawiMonotonic and Fatigue Flexural Behaviour of RCBeams Strengthened with Prestressed NSM CFRP Rods [PhDthesis] University of Waterloo Waterloo Ontario Canada2007

[12] R El-Hacha and K Soudki ldquoPrestressed near-surface mountedfibre reinforced polymer reinforcement for concrete structures- A reviewrdquo Canadian Journal of Civil Engineering vol 40 no11 pp 1127ndash1139 2013

[13] M Badawi and K Soudki ldquoFatigue behavior of RC beamsstrengthened with NSM CFRP rodsrdquo Journal of Composites forConstruction vol 13 no 5 pp 415ndash421 2009

[14] FOudah andR El-Hacha ldquoPerformance of RCbeams strength-ened using prestressed NSM-CFRP strips subjected to fatigueloadingrdquo Journal of Composites for Construction vol 16 no 3pp 300ndash307 2012

[15] KICT ldquoDevelopment of Bridge Strengthening Methods usingPrestressed FRP Compositesrdquo Tech Rep 2015

[16] T Hassan and S Rizkalla ldquoInvestigation of bond in concretestructures strengthened with near surface mounted carbonfiber reinforced polymer stripsrdquo Journal of Composites forConstruction vol 7 no 3 pp 248ndash257 2003

[17] M Blaschko ldquoBond Behavior of Strips Glued into Slitsrdquo inFRPRCS-6 pp 205ndash214 World Scientific Singapore 2003

[18] W T Jung Flexural Behavior of Reinforced Concrete BeamsStrengthened with NSM CFRP Reinforcements Considering theEquivalent Section [PhD thesis] Myongji University SeoulKorea 2009

[19] J S Park W T Jung Y H Park and C Y ldquoThe analysisfor reinforced concrete beams strengthened with externallyunbonded prestressed CFRP platesrdquo Journal of the Korea Societyof Civil Engineers vol 28 no 4A pp 439ndash445 2008

Submit your manuscripts athttpswwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of Polymer Science 9

Acknowledgments

This research was supported by a grant from ldquoa StrategicResearch Project funded by the Korea Institute of CivilEngineering and Building Technologyrdquo and ldquoUpgradingTechnology of Prestressed NSM Reinforcement System withCFRP Tendonrdquo

References

[1] M Rezazadeh H Ramezansefat and J Barros ldquoNSM CFRPprestressing techniques with strengthening potential for simul-taneously enhancing load capacity and ductility performancerdquoJournal of Composites for Construction vol 20 no 5 Article ID04016029 2016

[2] W T Jung J S Park and Y H Park ldquoAn experimental study onapplication of new prestressing system for NSM strengtheningtechniquerdquo inProceedings of the 9th International Symposium onFiber Reinforced Polymer Reinforcement for Reinforced ConcreteStructures (FRPRCSrsquo09) 2009

[3] W-T Jung J-S Park and S-H Kim ldquoA study on the behav-ior characteristics of curved FRP-concrete composite panelrdquoAdvanced Materials Research vol 557-559 pp 375ndash380 2012

[4] J S Park Y H Park I J Kwak W T Jung and S Y ChoildquoA Study on FRP Cable System for Cable Stayed Bridgerdquo RampDReport 08 Super-Long Span Bridge C02-01 Korea Institute ofConstruction Technology 2011

[5] W Jung J Park J Kang and M Keum ldquoFlexural behaviorof concrete beam strengthened by near-surface mounted cfrpreinforcement using equivalent section modelrdquo Advances inMaterials Science and Engineering vol 2017 pp 1ndash16 2017

[6] R EI-Hacha ldquoEffectiveness of near surface mounted frp rein-forcement for flexural strengthening of reinforced concretebeamsrdquo in Proceedings of the 4th International Conferenceon Advanced Composite Materials in Bridges and StructuresAlberta Canada 2004

[7] L De Lorenzis and J G Teng ldquoNear-surface mounted FRPreinforcement an emerging technique for strengthening struc-turesrdquoComposites Part B Engineering vol 38 no 2 pp 119ndash1432007

[8] H Nordin and B Taljsten ldquoConcrete beams strengthened withprestressed near surface mounted CFRPrdquo Journal of Compositesfor Construction vol 10 no 1 pp 60ndash68 2006

[9] W T Jung Y H Park and J S Park ldquoA study on the flexuralbehavior of reinforced concrete beams strengthened with NSMprestressed CFRP reinforcementsrdquo in Proceedings of the 8thInternational Symposium on FRP Reinforcement for ConcreteStructures (FRPRCSrsquo08) Patras Greece 2007

[10] H Nordin Flexural Strengthening of Concrete Structures withPrestressed Near Surface Mounted CFRP Rods Lulea Universityof Technology 2003

[11] M A BadawiMonotonic and Fatigue Flexural Behaviour of RCBeams Strengthened with Prestressed NSM CFRP Rods [PhDthesis] University of Waterloo Waterloo Ontario Canada2007

[12] R El-Hacha and K Soudki ldquoPrestressed near-surface mountedfibre reinforced polymer reinforcement for concrete structures- A reviewrdquo Canadian Journal of Civil Engineering vol 40 no11 pp 1127ndash1139 2013

[13] M Badawi and K Soudki ldquoFatigue behavior of RC beamsstrengthened with NSM CFRP rodsrdquo Journal of Composites forConstruction vol 13 no 5 pp 415ndash421 2009

[14] FOudah andR El-Hacha ldquoPerformance of RCbeams strength-ened using prestressed NSM-CFRP strips subjected to fatigueloadingrdquo Journal of Composites for Construction vol 16 no 3pp 300ndash307 2012

[15] KICT ldquoDevelopment of Bridge Strengthening Methods usingPrestressed FRP Compositesrdquo Tech Rep 2015

[16] T Hassan and S Rizkalla ldquoInvestigation of bond in concretestructures strengthened with near surface mounted carbonfiber reinforced polymer stripsrdquo Journal of Composites forConstruction vol 7 no 3 pp 248ndash257 2003

[17] M Blaschko ldquoBond Behavior of Strips Glued into Slitsrdquo inFRPRCS-6 pp 205ndash214 World Scientific Singapore 2003

[18] W T Jung Flexural Behavior of Reinforced Concrete BeamsStrengthened with NSM CFRP Reinforcements Considering theEquivalent Section [PhD thesis] Myongji University SeoulKorea 2009

[19] J S Park W T Jung Y H Park and C Y ldquoThe analysisfor reinforced concrete beams strengthened with externallyunbonded prestressed CFRP platesrdquo Journal of the Korea Societyof Civil Engineers vol 28 no 4A pp 439ndash445 2008

Submit your manuscripts athttpswwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Submit your manuscripts athttpswwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014