research article experimental assessment on the flexural

Research ArticleExperimental Assessment on the Flexural BondingPerformance of Concrete Beam with GFRP Reinforcing Barunder Repeated Loading

Minkwan Ju1 and Hongseob Oh2

1Department of Civil Engineering Kangwon National University 1 Joongang-ro Samcheok-si Gangwon 245-711 Republic of Korea2Department of Civil Engineering Gyeongnam National University of Science and Technology 150 Chilam-dong JinjuGyeongnam 660-758 Republic of Korea

Correspondence should be addressed to Hongseob Oh opera69cholcom

Received 14 April 2015 Accepted 7 June 2015

Academic Editor Joao M L Reis

Copyright copy 2015 M Ju and H Oh 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

This study intends to investigate the flexural bond performance of glass fiber-reinforced polymer (GFRP) reinforcing bar underrepeated loading The flexural bond tests reinforced with GFRP reinforcing bars were carried out according to the BS EN 12269-1 (2000) specification The bond test consisted of three loading schemes static monotonic and variable-amplitude loading tosimulate ambient loading conditions The empirical bond length based on the static test was 225mm whereas it was 317mmaccording to ACI 440 1R-03 Each bond stress on the rib is released and bonding force is enhanced as the bond length is increasedAppropriate level of bond length may be recommended with this energy-based analysis For the monotonic loading test the bondstrengths at pullout failure after 2000000 cycles were 104MPa and 65MPa respectively 63ndash70 of the values from the staticloading testThe variable loading test indicated that the linear cumulative damage theory onGFRP bondingmay not be appropriatefor estimating the fatigue limit when subjected to variable-amplitude loading

1 Introduction

Fiber-reinforced polymer (FRP) bars have been used widelyin reinforced concrete structures due to their many advan-tages FRP bars have superior material properties such asa high tensile strength and corrosion resistance From amaintenance point of view using FRP bars inside concretestructures is clearly cost-effective with respect to life cyclecosts Although the bond performance of FRP bars is weakerthan that of steel bars FRP bars have generated interestas an advanced substitute material for reinforced concretestructures

The bond in reinforced concrete is important in trans-ferring stress from the reinforcing bar to the concrete Tohave a composite action in reinforced concrete perfectbond capacity is required and conventional steel bars areusually considered to satisfy this bond performance Unlikeconventional steel reinforcing bars however determiningthe performance bond capacity of FRP reinforcing bars is

difficult The bond between concrete and FRP reinforcingbars is complex and several factors influence the bond char-acteristics According to previous research the key factors arethe concrete compressive strength bar diameter embedmentlength geometry and surface treatment scheme of the FRPreinforcing bar temperature changes and environmentalconditions [1]

Many experimental studies have been conducted to inves-tigate the bond performance of FRP reinforcing bars usingpullout tests [2ndash7] Most of these have been monotonic anduniaxial tests based on the ASTM standard Beam tests arebelieved to more realistically simulate the stress transfer ofreinforced concrete subjected to flexural bending but fewstudies have been reported determining the fatigue bondcharacteristics of FRP reinforcing bars which is essential tounderstand reinforced concrete structures in a service stateunder repeated monotonic and amplitude loading Investi-gating bond characteristics of the bond surface is importantwherein longitudinal friction of the FRP reinforcing bar is

Hindawi Publishing CorporationInternational Journal of Polymer ScienceVolume 2015 Article ID 367528 11 pageshttpdxdoiorg1011552015367528

2 International Journal of Polymer Science

(a) Conventional steel reinforcing bar

GFRP core

Deformed rib withmilled glass fiber

(b) Newly developed GFRP reinforcing bar

P = lug pitch120572 = 80∘

d

Lug

120572P = 063d t = 021d

014d

d998400

w = 023d

014d

GFRP core

Polymer rib withmilled glass fiber

(c) Design detail of GFRP reinforcing bar

Figure 1 GFRP reinforcing bar used in this study

usually concentrated when subjected to repeated externalloading of the reinforced concrete beam

This study investigated the bond performance of GFRPreinforcing bars subjected to fatigue loading The beam testsfor bonding were carried out according to the BS EN 12269-1 [8] specification The test variables were the three types ofbond length For static and monotonic loading tests maxi-mum bond strength and slip were analyzed and a reductionfactor in bond strength was suggested experimentally toevaluate safety in bond design subjected to fatigue loadingFor variable-amplitude loading tests the fatigue limit wasevaluated with an S-N curve based on Minerrsquos theory andits application to the nonlinear cumulative damage for thebonding behavior of glass fiber-reinforced polymer (GFRP)reinforcing bars subjected to variable-amplitude loading isdiscussed

2 Experimental Program

21 Description of Properties of GFRP Reinforcing Bars SteelReinforcing Bars and Concrete TheGFRP reinforcing bar asdepicted in Figure 1 used consisted of continuous longitudi-nal glass fibers of 67 volume fraction in a thermosettingepoxy [9] To mold the surface pattern and to enhance thebond performance of the GFRP reinforcing bar its externallayer was manufactured by mixing milled glass fiber andepoxy at a ratio of 1 1 and it was cured for 15min at atemperature above 160∘C To enhance bond performance thesurface pattern of the developed GFRP reinforcing bar was

treated to have ribs similar to those of a steel reinforcing barusing epoxy resin containingmilled glass fiber bymechanicalpressing after pultrusion of the FRP core section The ribsection was a mixture of epoxy resin and milled glass fibersThe external deformed-rib arrangement angle was set at 80∘The rib height and spacing were chosen based on a literaturereview to obtain optimalmechanical performance in terms ofbond and tension characteristics [10] The GFRP reinforcingbar used for the tensile area had a nominal diameter of953mm and a design tensile strength which is a guaranteedtensile strength multiplied by the environmental reductionfactor in compliance with ACI 440 1R-06 of fu (GFRP) =616MPa its modulus of elasticity was 429GPa [11]

22 Flexural Bond Strength from the Beam Test The testmethod and details for evaluating the flexural bond strengthof theGFRP reinforcing bar adopted the scheme of the BritishStandard [8]The beam test in bonding is considered to morerealistically mimic the stress conditions of the reinforcedconcrete (RC) structure subjected to bending Tighiouartet al [12] conducted beam tests in bonding according tothe RILEM specification The specimen consisted of tworectangular blocks joined at the top by a steel ball jointThe design concrete compressive strength is 27MPa Thisspecimen detail may not be appropriate for fatigue but fora monotonic loading test due to the possibility of the stressconcentration in the concrete at the ball joint Thus for thefatigue bond test in this study the test scheme of BSEN 12269-1 [8] was adopted whereby a concrete compressive block wasused to create the stress distribution in the fatigue test

International Journal of Polymer Science 3

P

C = 30

150

200PVC500

1300

100

50

lb1 lb2 lb3lb1 lb2 lb3

50050

LVDT

Concrete beam

GFRP bar

Strain gauge BondedBonded

Figure 2 Specimen geometry of the BS beam test

C

T

j

P

lb1 lb2 lb3

Bonded

500mm

a = 550mm

180mm

170mm

30mm

Figure 3 Force equilibrium of cross section at the mid-span

The size of the test specimens was 180 times 200 times 1300mmand the major variables according to bond length (119897

119887) are

shown in Figure 2 The lower section of the mid-span in thebeam was formed as a semicircular type to prevent stressconcentration caused by flexural cracks tips Bond lengthswere set at 119897

1198871= 5119889

119887(45mm) 119897

1198872= 10119889

119887(90mm) and

1198971198873= 15119889

119887(135mm) where 119889

119887is the diameter of the FRP

reinforcing bar for simulating pullout failure of the GFRPreinforcing bar As shown in Figure 2 the unbounded regionof the FRP reinforcing bar in the concrete beam was securedby PVC pipes that had a slightly larger inner diameter thanthe diameter of the GFRP reinforcing bar The test beam wasloaded using a 250 kN hydraulic actuator (MTS) and wasexecuted with a four-point loading method The unloadedslip was measured at both ends of the specimens (Figure 2)

Figure 3 illustrates the force equilibrium condition andits relationship is shown in (1) Once the tensile load (119879) isapplied the tensile stress (120591) at the load level is calculatedby dividing by the bond surface area according to BS EN12269-1 [8] The optimal bond length is defined as theminimum length to transfer the ultimate load from the GFRP

reinforcing bar to the concrete through the bond surfaceConsider

119872 = 119875 sdot 119886 = 119862 sdot 119895 = 119879 sdot 119895 = 119864frp sdot 120576frp sdot 119895 (1)

where 119879 = tensile load of the GFRP reinforcing bar (kN) 119875= ultimate applied load (kN) 120576frp = measured strain of thesteel or GFRP reinforcing bar 119864frp = modulus of elasticityof the steel or GFRP reinforcing bar (MPa) 119886 = shear span(mm) and 119895 = distance between the resulting tensile andcompressive loads (mm)

As mentioned above the fatigue loading applied maxi-mum stress level with the ratio to the static test results asfollows 60 70 75 80 85 and 90 of the peak loadof each variable The minimum stress level was consideredto be 10 of the applied maximum load All specimens weretested at 3Hz and sinusoidal loading was controlled up tofatigue failure or 2000000 loading cycles Data acquisitionfor calculating bond stress was performed after finishing thecycle controls


Table 1 Experimental bond strength and slip at peak stress

Measured maximum bond stress (MPa) Slip at peak bond stress (mm)From force equilibrium From reinforcing bar strain

5119889119887

1634 1263 01931511 906 0125

10119889119887

11 761 01351222 688 0168

15119889119887

959 577 0050807 603 0060

0

2

4

6

8

10

12

14

16

0 1 2 3 4

Flex

ural

bon

d str

engt

h (M

Pa)

Unloaded end slip (mm)

5db force equilibrium10db force equilibrium15db force equilibrium

(a)

0

2

4

6

8

10

12

14

16

0 1 2 3 4

Flex

ural

bon

d str

engt

h (M

Pa)


5db FRP strain10db FRP strain15db FRP strain

(b)

Figure 4 Relationship between flexural bond stress and slip under static loading conditions

3 Test Results of the Static Loading Test

The relationship between flexural bond stress and slip fromthe static test performed according to Oh et al [11] issummarized in Figure 4 and Table 1 The bond stress of eachspecimen was expressed under force equilibrium conditionsand reinforcing bar strain According to the static loadingtest the bond strength determined using the measured strainof the GFRP reinforcing bar was found experimentally tobe lower than that using equilibrium theory This differencemight have been caused by incomplete bond stress transfer tothe concrete The reason was analyzed in terms of the bondbehavior of the GFRP reinforcing bar and the change in theneutral axis of the beam section during loading

As reported by other researchers the bond strengthcalculated from force equilibrium at the beam section of themid-span of the specimen is slightly higher than the strengthcalculated from FRP strain The work energy of the pulloutaction of FRP reinforcing bar indicates the capacity forenergy dissipation at the interface between concrete and thesurface of reinforcing barWhile the bond strength decreasesaccording to the increase in bond length total work energy

defined by the area of loads and slip curves of the specimenincreases (Figure 5)

The required development length to ensure reinforcingbar strength should be calculated under force equilibriumconditions for the beam specimen and also demonstrated bythe equation 119897

119887= 119889119887119891fu185 as reported in ACI 440 1R-

03 where 119897119887is the bond length 119889

119887is the nominal diameter

of the GFRP reinforcing bar and 119891fu is the designed tensilestrength of the GFRP reinforcing bar The experimentallength obtained from the regression data based on the testresults and development length according to ACI 440 isshown in Figure 6 Both the regression curve from test resultsand the analytical bond length from (1) curve tended todecrease the bond strength as the bond length increasedThe large discrepancy at 50mm bond length was due tothe short bond length and bond perimeter which could beconservative as the bond length is increased further Theminimum bond length that the GFRP reinforcing bar canafford to contribute to the tensile strength of the concrete was225mm from the crossing point between the two curves byregression and (1) The bond length however was calculatedas 317mm according to ACI 440 1R-03


Table 2 Stress levels in the fatigue bond test

Specimens Bond strength atstatic test (MPa)

Applied stresslevel ()

Applied bondstress (MPa)

Slip at ultimateload (mm)

Number ofcycles

Residual bondstrength after 2million loadings

(MPa)

Failure mode

5119889119887

(45mm) 151

70758090

114122130147

0175mdashmdashmdash

20000001516231292683804

105mdashmdashmdash

Plowast

10119889119887

(90mm) 102 7080

7788

0083mdash

200000081063

64mdash Plowast

15119889119887

(135mm) 75

60758085

48607277

mdashmdashmdashmdash

20000001981582193972114413

39mdashmdashmdash

CSlowastlowast

lowastPullout failure and lowastlowastconcrete splitting failure

5 10 152

3

4

5

6

7

376676 372344

466044

152

116

882

0

4

8

12

16

20

Tota

l wor

k en

ergy

(Nm

m)

Max

bon

d str

engt

h (M

Pa)

times104

Proportional bond length to the bar diameter (timesdb)

Figure 5 Totalwork energy andmaximumbond strength accordingto the embedded bond length

0

5

10

15

20

25

30

35

0 50 100 150 200 250 300 350

Flex

ural

bon

d str

engt

h (M

Pa)

Bond length (mm)

From the force equilibrium

Regression line from the experimental results

ACI 440 1R-03

The crossing point of the test and theory

Figure 6 Bond strength and bond length relationship by calculationand test results

Figure 7 Pullout failure

4 Test Results of the MonotonicFatigue Loading Test

41 Bond Strength When Subjected to Fatigue Loading Eachspecimen was tested for the designated level of stress assummarized in Table 2 and 10 specimens in total were testedTwo types of failure pattern were investigated typical pulloutfailure (5119889

119887 10119889119887) and concrete splitting failure at the end

of bonded region of the reinforcing bar (15119889119887) (Figures 7

and 8) Pullout failure occurs when the bond stress betweenthe concrete and GFRP reinforcing bar exceeds the stressresulting from the tensile load on the bar Concrete splittingfailure must be caused by insufficient concrete strengtheven though the embedded length of the reinforcing baris sufficient to perform the composite action As shown inFigure 6 no shear-off of the ribs on the GFRP reinforcingbar occurred with the pullout failure indicating that theinterlocking mechanism with the concrete is valid

The bond strength was determined at the fatigue limitof 2000000 cycles at which point a failure test was finallyappliedThe 5119889

119887and 10119889

119887specimens showed the fatigue limit

at a stress level of 70 The number of cycles increased asthe development length was longer For the pullout failurespecimens of 5119889

119887and 10119889

119887 the bond strengths at failure

testing after 2000000 cycles were 105MPa and 64MPa


Figure 8 Concrete splitting failure

0

2

4

6

8

10

12

14

16

0 01 02 03 04 05 06 07 08 09 1

Bond

ing

stren

gth

(MPa

)

Slip (mm)

Static bonding test1100010000

10000010000002000000Static failure test

Figure 9 Bond stress-slip relationship of the 5119889119887

specimen under70 stress level of the ultimate strength

respectively which is 63ndash70 of those from the static bondtestThis differencewas caused by repeated stress on the bondsurface so that fatigue stress weakened the adhesive capacitybetween the concrete and surface of the GFRP bar includingribs so that it degraded the bonding performance For the15119889119887specimen themode of failurewas concrete splittingThe

bond length over 15119889119887can be concluded to be close to having

sufficient bonding performance for theGFRP reinforcing barThis is consistent with the results of the static loading testwhereby the bond strength difference between the calculatedand measured strain on the GFRP reinforcing bar and thatusing equilibrium theory keeps decreasing as the bond lengthincreases

42 Fatigue Bond Strength and Slip Relationship Bond stressand slip relationships under fatigue loading are shown inFigures 9 and 10 including the results of the static bondtests The 15119889

119887specimen was not included for slip behavior

after 2000000 cycles due to the concrete splitting modeof failure The slip amount at 2000000 cycles for the 10119889

119887

specimen was not measured due to a data recording errorAccording to Oh et al [11] the bond performance of the steel

0

2

4

6

8

10

12

14

16

0 01 02 03 04 05 06

Bond

ing

stren

gth

(MPa

)

Slip (mm)



Slip was not recorded temporarilyat 2000000 cycles



reinforcing bar was better than that of the GFRP reinforcingbar considering bars of the same diameter due to enhancedshear action of the GFRP rib For the fatigue test as thenumber of repeated cycles increased the residual slip amountalso increased although its scale was very small The 10119889

119887

specimen showed less than 50 slip versus the 5119889119887specimen

at the ultimate bond strength As the bond length increasedthe bond strength decreased [13 14]Thebond strength can bedefined as a mechanical performance of the rib As the bondlength is shorter the bond strength at the rib is increased Ifthe bond length is longer however the bond strength at therib is decreased due to the stress distribution Consequentlythe ribs with longer bond lengths can stably contribute stresstransference to the concrete with much higher tensile stressof the reinforcing bar than with a short bond length

43 Fatigue Limit of GFRPReinforcing Bar Bonding Compar-ing the 10119889

119887specimen with the 5119889

119887specimen at 2000000

cycles in Figures 8 and 9 the maximum slip of the 10119889119887

specimen was found to be less than that of the 5119889119887specimen

This indicated that as the bond length was longer themaximum bond strength resulted in the shorter slip Thiswas confirmed with experimental results of maximum slipsof 0175mm for 5119889

119887and 0083mm for 10119889

119887 The slip limit

for longer bond length specimen of the GFRP reinforcing barat 2000000 cycles can be estimated it will diminish with adecreasing rate close to that for the 5119889

119887and 10119889

119887specimens

For the fatigue test the fatigue limit state can be estimatedfrom the S-N curve based on Minerrsquos theory which is basedmostly on linear cumulative damage concepts as proposed byPalmgren and Miner [15] Figure 11 shows the log-scaled S-Ncurve and regression analysis from the results of the fatiguetests for the 5119889

119887and 10119889

119887specimens For S-N curve analysis

the fatigue limit of the bonding of the GFRP reinforcingbar can be investigated for pullout failure The fatigue limit


Table 3 Estimation of fatigue limit stress based on a regressionanalysis

Specimens Regression formula Fatigue limit stressat 10000000 cycles

5119889119887

minus265 ln(119909) + 11007 68010119889119887

minus3119 ln(119909) + 11526 650

50

60

70

80

90

100

Stre

ss le

vel (

)

1 102 104 106 108

Static test after 2 times 106 cycles (5db and 10db)

Static test after 2 times 106 cycles (5db

Fatigue life (Nf)

15db (135mm)10db (90mm)5db (45mm)

10db and 15db)

Figure 11 S-N relationship of the flexural bond test specimens

state of bonding is useful in designing and analyzing flexuralreinforced concrete members especially those reinforcedwith GFRP reinforcing bars Table 3 shows the estimatedfatigue limit stress by regression analysis

5 Test Results of the Variable-AmplitudeLoading Test

Due to the uncertain characteristic of the bond strengthof the FRP reinforcing bar investigating only monotonicloaded fatigue test is not sufficient Authors conducted theflexural fatigue bond test under variable-amplitude loadingcondition to evaluate the real bond fatigue performance Onecan simulate the accelerated effect of accumulated damage onbond strength of the GFRP reinforcing bar by subjecting it tovariable-fatigue loading conditions Table 4 shows the appliedload levels and cases for the variable-amplitude loading testEach specimen was tested for the designated variable loadingcase and in total six specimens were tested for 5119889

119887and 15119889

119887

Loading was applied based on the designated proportion ofthe maximum bond strength as in the monotonic loadingtest The loading sequence however was set as shown inTable 4Theminimum load level was considered to be 15 ofthe failure number of cycles (119873

119891) and the variable-amplitude

load was initiated at this level Variable load cases 1 and 2are the upward (low 75 to high 80) and downward (high80 to low 75) load cases respectively These loading caseswere performed to investigate the accumulated damage effectaccording to the loading sequence magnitude Variable load

case 3 is an upward case including two steps of the minimumload level of 015119873

119891The experimental results from these load

cases were analyzed using the linear damage theory of fatigueFigure 11 shows the relationship of applied bond stress

and unbounded end slip for test specimens with bond lengthsof 45mm and 135mm The two specimens have differentperformance limits such as pullout and concrete splittingfailure For this reason the unloaded end slips before theconcrete splitting failure of the 15119889

119887specimenwere compared

with those of the 5119889119887specimen The 5119889

119887specimen showed a

sudden increase in slip in the downward load case (80 to 75)as it approached failureThe 15119889

119887specimen however showed

no such sudden increase and the slip at failure was stableat 02mm As the applied load level was increased the 5119889

119887

specimen with the shorter bond length was more sensitiveto causing a larger slip Figure 12 shows the relationshipbetween cumulative end slip and normalized relative fatiguelife (119899

119891119873119891)

Figure 13 illustrates the cumulative end-slip increaseaccording to the relative fatigue life for the monotonic andthe variable-amplitude loading test The cumulative end slipunder variable-amplitude loading condition compared withthat of monotonic loading condition exhibited a suddenincrease of slip at the moment of the specific fatigue lifeIn the case of the FRP reinforcing bar verifying the bondcharacteristics based on bond length is more importantthan the conventional steel reinforcing bar subjected to thevariable-amplitude load regarding the real loading frequencyof the traffic volume Table 5 summarizes the result ofestimation of fatigue life by the Palmgren-Miner rule whichis commonly used to calculate the cumulative fatigue damageon the following equation

119863 =

119896

sum

119894=1

119899119894

119873119894

(2)

where 119899119894= number of loading cycles at a given stress level

sigma 119894119873119894= number of cycles to failure at sigma 119894 and 119863 =

total damage on fatigue (usually considered to be 1 at fatiguefailure)

6 Results and Discussions

The bond length of the GFRP reinforcing bar in this study isldquosaferrdquo than that mandated by ACI 440 1R-03 and the outerribs can sufficiently resist the shear friction against the tensilestress of the GFRP reinforcing bar For purposes of structuraldesigns the bond characteristics should also be confirmedwhen subjected to repeated loading conditions

The work energy of the pullout action of FRP reinforcingbar indicates the capacity for energy dissipation at theinterface between concrete and the surface of reinforcing barWhile the bond strength decreases according to the increasein bond length total work energy defined by the area of loadsand slip curves of the specimen increases (Figure 5) Thismeans that each bond stress on the rib is released andbondingforce is enhanced as the bond length is increased Appropriatelevel of bond length may be recommended with this energy-based analysis


0

2

4

6

8

10

12

14

16

0 1 2 3 4

Load

s (kN

)

Deflection (mm)

75_1 cycle 75_100 cycles75_10000 cycles 75_100000 cycles75_227435 cycles 80_1 cycle80_100 cycles 80_10000 cycles

(a) 075120591max rarr 080120591max(5119889119887)

0

5

10

15

20

25

0 1 2 3 4

Load

s (kN

)

Deflection (mm)

75_1 cycle 75_100 cycles75_10000 cycles 75_297237 cycles80_1 cycle 80_100 cycles80_100000 cycles

(b) 075120591max rarr 080120591max(15119889119887)

0 1 2 3 4Deflection (mm)

0

2

4

6

8

10

12

14

16

Load

s (kN

)

80_1 cycle 80_100 cycles80_4390 cycles 75_1 cycle75_100000 cycles 75_200000 cycles75_400000 cycles

(c) 080120591max rarr 075120591max(5119889119887)


0

5

10

15

20

25Lo

ad (k

N)

80_1 cycle 80_100 cycles80_10000 cycles 80_29096 cycles75_1 cycle 75_10000 cycles75_100000 cycles 75_400000 cycles

(d) 080120591max rarr 075120591max(15119889119887)


0

2

4

6

8

10

12

14

16

Load

s (kN

)

75_1 cycle 75_100 cycles75_10000 cycles 75_227435 cycles80_1 cycle 80_4390 cycles90_1 cycle 90_1000 cycles

(e) 075120591max rarr 080120591max rarr 090120591max(5119889119887)


0

5

10

15

20

25

Load

s (kN

)

75_1 cycle 75_100 cycles75_10000 cycles 75-100000 cycles75_297237 cycles 80_1 cycle80_29096 cycles 85_1 cycle85_100 cycles 85_50000 cycles

(f) 075120591max rarr 080120591max rarr 085120591max(15119889119887)

Figure 12 Relationship between applied loads and cumulative mid-deflection under various loading steps


Table 4 Stress level of the fatigue bond test

Load levels and cases Applied load history Loading sequencesVariable load case 1 075120591max (015119873119891) rarr 08120591max (until failure) Low rarr highVariable load case 2 08120591max (015119873119891) rarr 075120591max (until failure) High rarr lowVariable load case 3 075120591max (015119873119891) rarr 08120591max (015119873119891) rarr 085120591max or 085120591max (until failure) Low rarr high 1 rarr high 2

0

01

02

03

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)

Normalized relative fatigue life (nNf)

5db_07515db_0755db_08

15db_085db_09

(a)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)


5db_075ndash0815db_075ndash08


(b)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)


5db_075ndash08ndash0915db_075ndash08ndash085

(c)

Figure 13 Cumulative end-slip increase according to the relative fatigue life

Table 5 Linear cumulative damage of the specimens under anamplitude loading condition

Load case 1198631

1198632

1198633

sum119863119894

5119889119887

Case 1 015 089 mdash 104Case 2 015 027 mdash 042Case 3 015 015 096 126

15119889119887

Case 1 015 116 mdash 131Case 2 015 021 036Case 3 015 015 071 101

Compared with the static loading test the bond strengthdecreased markedly for the 5119889

119887and 10119889

119887specimens up to

a maximum 63ndash70 as noted above This degraded bondstrength was caused by the residual slip resulting from therepeated loading Repeated loading of a flexural memberreinforced with GFRP reinforcing bar was concluded to affectthe loss of bond strength which is a factor usually consideredin the design of the bond

At the assumed fatigue cycles of 10000000 the fatiguelimit stresses for 5119889

119887and 10119889

119887specimens were 680 and

650 respectively These results showed that the GFRPreinforcing bar had sufficient bond performance in a repeatedloading state such as vehicular traffic to be used in the designof concrete flexural members

Initial damage was calculated by considering the appliedload level of 015119873

119891 For the total damage on fatigue two

apparent differences were detectedThe low-high cases (cases1 and 3) showed total damage over 10 according to testresults of the fatigue failure The high-low case (case 2)however showed total damage still under 10 even thoughthe specimen had already failedThis result indicates that thefatigue performance was more vulnerable when a high loadis applied prior to a low load on the structure The linearcumulative damage theory based on thePalmgren-Miner rulemay not be appropriate for estimating the fatigue limit whensubjected to variable-amplitude loading

61 Reduction Factor of the Fatigue Bond Strength From thefatigue bond test the relationship between the reductionin bond strength and the residual slip at maximum bondstrength in fatigue at 2000000 cycles was investigated Asthe slip increased the bond strength was found to decrease


Reduction of

Residual slip

Slip

Bond

ing

stren

gth

Fatigue test

Static test

Maximum bonding strength 1205911


bonding strength (1205911-1205912)Sbfrp

Figure 14 Diagram of the reduction factor of bond stiffness for anFRP reinforcing bar

Thus the reduction in bond strength was proportional tothe amount of residual slip which means that bond stiffnessaccording to repeated loading decreases This relationshipcan be redefined using an energy concept to calculate half thearea of the 119909-119910 graph

In this study a reduction factor for bond stiffness ofthe FRP reinforcing bar 119878

119887 frp can be defined by an energyconcept using the area of the shaded section in Figure 14Theconceptual formula is as follows

119878119887 frp

=

1

2

[a reduction in bond strength (1205911minus 1205912) (MPa)

times the residual slip (mm)]

(3)

119878119887 frp is suggested for evaluating the reduced capacity inbonding of an FRP reinforcing bar reinforced in a concreteflexural member when it is serviced under an ambientrepeated loading state such as vehicle load The performancestandard for fatigue bonding of the FRP reinforcing barshould be used in designing the member The reducedcapacity under fatigue loading must be evaluated quanti-tatively because of the various types of rib shapes for theFRP reinforcing bar so that the rib shapes directly affectdetermining the bond capacity especially in fatigue loadingBy applying (3) to the results of the 5119889

119887and 10119889

119887specimens

119878119887 frp for the 5119889

119887and 10119889

119887specimens was found to be 041

and 016 respectively which means that as the bond lengthis longer the reduction in bond stiffness decreases Thus aquantitative evaluation indicated that the bond stress can betransferred to the concrete well under fatigue loading

Using this factor for the reduced capacity of bonding ofFRP reinforcing bars one can check the reduction rate ofbonding of FRP reinforcing bars under fatigue loading Fora more reliable evaluation 119878

119887 frp should be formulated as afunction of various experimental data so that the nonlinearityof the relationship between the reduced bond strength andthe residual slip can be confirmed

7 Conclusions

In this study we investigated the bond performance of GFRPreinforcing bars under fatigue loading The fatigue test wasconducted until 2000000 cycles and the bond strengthand slip relationship were examined The conclusions are asfollows

(1) For the static loading test the bond length wasevaluated as 225mm whereas it was 317mm according toACI 440 1R-03 The bond length of the GFRP reinforcing barin this study well satisfied the ACI 440 1R-03 limit and theouter ribs sufficiently resisted the shear friction against thetensile stress of the GFRP reinforcing bar Each bond stresson the rib is released and bonding force is enhanced as thebond length is increased Appropriate level of bond lengthmay be recommended with this energy-based test result Forthe purposes of structural design these bond characteristicsshould be further confirmed when subjected to repeatedloading conditions

(2) For the pullout failure specimens the bond strengthsat failure testing after 2000000 cycles were 104MPa and65MPa respectively which is 63ndash70 when compared withthose from the static bond test This was caused by repeatedstress on the bond surface so that fatigue stress weakened theadhesive capacity between the concrete and the surface of theGFRP reinforcing bar Thus FRP bonding in designs shouldbe checked with respect to the fatigue behavior of the flexuralmember

(3) In this study a reduction factor for bond stiffness forthe FRP reinforcing bar 119878

119887 frp was suggested experimentallyUsing this factor for the reduced capacity of bonding of FRPreinforcing bars one can quantitatively check the expectedreduced bonding of the FRP reinforcing bar under fatigueFor amore reliable evaluation 119878

119887 frp should be formulated as afunction of various experimental data so that the nonlinearityof the relationship between the reduced bond strength andresidual slip can be confirmed

(4) For the variable loading test the linear cumulativedamage theory on GFRP bonding was found to perhaps notbe appropriate to estimate the fatigue limit when subjectedto variable-amplitude loadingTheGFRP reinforcing bar wasconcluded to have sufficient bond performance in a repeatedloading state such as vehicular traffic that is it can be usedin designing concrete flexural members In future studiesfatigue limit estimation should be researched for bonding ofGFRP reinforcing bars under ambient loading conditions

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Thisworkwas supported by research grants of Korea Instituteof Marine Science amp Technology Promotion (PJT200493)and Korea Institute of Energy Technology Evaluation andPlanning (0000000015513)


References

[1] E CosenzaGManfredi andR Realfonzo ldquoBehavior andmod-eling of bond of FRP rebars to concreterdquo Journal of Compositesfor Construction vol 1 no 2 pp 40ndash51 1997

[2] E Cosenza G Manfredi and R Realfonzo ldquoDevelopmentlength of FRP straight rebarsrdquo Composites Part B Engineeringvol 33 no 7 pp 493ndash504 2002

[3] Z Achillides and K Pilakoutas ldquoBond behavior of fiber rein-forced polymer bars under direct pullout conditionsrdquo Journalof Composites for Construction vol 8 no 2 pp 173ndash181 2004

[4] M Baena L Torres A Turon and C Barris ldquoExperimentalstudy of bond behaviour between concrete and FRP bars usinga pull-out testrdquo Composites Part B Engineering vol 40 no 8pp 784ndash797 2009

[5] ZHe andG-W Tian ldquoProbabilistic evaluation of the design de-velopment length of a GFRP rod pull-out from concreterdquo Jour-nal of Engineering Structures vol 33 no 10 pp 2943ndash2952 2011

[6] C G Papakonstantinou P N Balaguru and Y AuyeungldquoInfluence of FRP confinement on bond behavior of corrodedsteel reinforcementrdquo Cement and Concrete Composites vol 33no 5 pp 611ndash621 2011

[7] Y Ding X Ning Y Zhang F Pacheco-Torgal and J B AguiarldquoFibres for enhancing of the bond capacity betweenGFRP rebarand concreterdquo Construction and Building Materials vol 51 pp303ndash312 2014

[8] British Standard ldquoDetermination of the bond behavior betweenreinforcing steel and autoclaved aerated concrete by the beamtestrdquo BS EN EN 12269-1 2000

[9] J Sim H Oh D Moon and M Ju ldquoA hybrid fiber reinforcedplastic rebar having a optic sensor for concreterdquo Patent No100709292 2006 (Korean)

[10] DMoonBond behavior of newly developed deformedGFRP bars[PhD thesis] Hanyang University Seoul Republic of Korea2004

[11] H Oh J Sim T Kang and H Kwon ldquoAn experimental studyon the flexural bonding characteristic of a concrete beam rein-forced with a GFRP rebarrdquo KSCE Journal of Civil Engineeringvol 15 no 7 pp 1245ndash1251 2011

[12] B Tighiouart B Benmokrane and D Gao ldquoInvestigation ofbond in concrete member with fibre reinforced polymer (FRP)barsrdquo Construction and Building Materials vol 12 no 8 pp453ndash462 1998

[13] E Makitani I Irisawa and N Nishiura ldquoInvestigation of bondinconcrete member with fibre reinforced polymer barsrdquo inProceedings of the International Symposium Fibre-Reinforced-Plastic Reinforcement for Concrete Structures ACI SP-138 pp315ndash331 1993

[14] A Nanni M M Al-Zahrani S U Al-Dulaijan C E Bakis andT E Boothby ldquoBond of FRP reinforcement to concreterdquo in Pro-ceedings of the 2nd International RILEM Symposium (FRPRCS-2rsquo95) pp 135ndash145 London UK 1995

[15] J Schijve Fatigue of Structures andMaterials Kluwer AcademicPublishers Dordrecht The Netherlands 2001

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


(a) Conventional steel reinforcing bar

GFRP core

Deformed rib withmilled glass fiber

(b) Newly developed GFRP reinforcing bar

P = lug pitch120572 = 80∘

d

Lug

120572P = 063d t = 021d

014d

d998400

w = 023d

014d

GFRP core

Polymer rib withmilled glass fiber

(c) Design detail of GFRP reinforcing bar

Figure 1 GFRP reinforcing bar used in this study

usually concentrated when subjected to repeated externalloading of the reinforced concrete beam

This study investigated the bond performance of GFRPreinforcing bars subjected to fatigue loading The beam testsfor bonding were carried out according to the BS EN 12269-1 [8] specification The test variables were the three types ofbond length For static and monotonic loading tests maxi-mum bond strength and slip were analyzed and a reductionfactor in bond strength was suggested experimentally toevaluate safety in bond design subjected to fatigue loadingFor variable-amplitude loading tests the fatigue limit wasevaluated with an S-N curve based on Minerrsquos theory andits application to the nonlinear cumulative damage for thebonding behavior of glass fiber-reinforced polymer (GFRP)reinforcing bars subjected to variable-amplitude loading isdiscussed

2 Experimental Program

21 Description of Properties of GFRP Reinforcing Bars SteelReinforcing Bars and Concrete TheGFRP reinforcing bar asdepicted in Figure 1 used consisted of continuous longitudi-nal glass fibers of 67 volume fraction in a thermosettingepoxy [9] To mold the surface pattern and to enhance thebond performance of the GFRP reinforcing bar its externallayer was manufactured by mixing milled glass fiber andepoxy at a ratio of 1 1 and it was cured for 15min at atemperature above 160∘C To enhance bond performance thesurface pattern of the developed GFRP reinforcing bar was

treated to have ribs similar to those of a steel reinforcing barusing epoxy resin containingmilled glass fiber bymechanicalpressing after pultrusion of the FRP core section The ribsection was a mixture of epoxy resin and milled glass fibersThe external deformed-rib arrangement angle was set at 80∘The rib height and spacing were chosen based on a literaturereview to obtain optimalmechanical performance in terms ofbond and tension characteristics [10] The GFRP reinforcingbar used for the tensile area had a nominal diameter of953mm and a design tensile strength which is a guaranteedtensile strength multiplied by the environmental reductionfactor in compliance with ACI 440 1R-06 of fu (GFRP) =616MPa its modulus of elasticity was 429GPa [11]

22 Flexural Bond Strength from the Beam Test The testmethod and details for evaluating the flexural bond strengthof theGFRP reinforcing bar adopted the scheme of the BritishStandard [8]The beam test in bonding is considered to morerealistically mimic the stress conditions of the reinforcedconcrete (RC) structure subjected to bending Tighiouartet al [12] conducted beam tests in bonding according tothe RILEM specification The specimen consisted of tworectangular blocks joined at the top by a steel ball jointThe design concrete compressive strength is 27MPa Thisspecimen detail may not be appropriate for fatigue but fora monotonic loading test due to the possibility of the stressconcentration in the concrete at the ball joint Thus for thefatigue bond test in this study the test scheme of BSEN 12269-1 [8] was adopted whereby a concrete compressive block wasused to create the stress distribution in the fatigue test


P

C = 30

150

200PVC500

1300

100

50


50050

LVDT

Concrete beam

GFRP bar



C

T

j

P

lb1 lb2 lb3

Bonded

500mm

a = 550mm

180mm

170mm

30mm



119887) are


1198871= 5119889

119887(45mm) 119897

1198872= 10119889

119887(90mm) and

1198971198873= 15119889

119887(135mm) where 119889











5119889119887

1634 1263 01931511 906 0125

10119889119887

11 761 01351222 688 0168

15119889119887

959 577 0050807 603 0060

0

2

4

6

8

10

12

14

16

0 1 2 3 4

Flex

ural

bon

d str

engt

h (M

Pa)



(a)

0

2

4

6

8

10

12

14

16

0 1 2 3 4

Flex

ural

bon

d str

engt

h (M

Pa)



(b)

















Number ofcycles


(MPa)

Failure mode

5119889119887

(45mm) 151

70758090

114122130147

0175mdashmdashmdash

20000001516231292683804

105mdashmdashmdash

Plowast

10119889119887

(90mm) 102 7080

7788

0083mdash

200000081063

64mdash Plowast

15119889119887

(135mm) 75

60758085

48607277


20000001981582193972114413

39mdashmdashmdash

CSlowastlowast


5 10 152

3

4

5

6

7

376676 372344

466044

152

116

882

0

4

8

12

16

20

Tota

l wor

k en

ergy

(Nm

m)

Max

bon

d str

engt

h (M

Pa)

times104



0

5

10

15

20

25

30

35

0 50 100 150 200 250 300 350

Flex

ural

bon

d str

engt

h (M

Pa)

Bond length (mm)



ACI 440 1R-03










119887and 10119889



119887and 10119889





0

2

4

6

8

10

12

14

16

0 01 02 03 04 05 06 07 08 09 1

Bond

ing

stren

gth

(MPa

)

Slip (mm)











119887


0

2

4

6

8

10

12

14

16

0 01 02 03 04 05 06

Bond

ing

stren

gth

(MPa

)

Slip (mm)







119887









119887and 0083mm for 10119889



119887and 10119889

119887specimens


119887and 10119889






5119889119887

minus265 ln(119909) + 11007 68010119889119887

minus3119 ln(119909) + 11526 650

50

60

70

80

90

100

Stre

ss le

vel (

)

1 102 104 106 108



Fatigue life (Nf)

15db (135mm)10db (90mm)5db (45mm)

10db and 15db)





119887and 15119889

119887














119887


119891119873119891)


119863 =

119896

sum

119894=1

119899119894

119873119894

(2)








0

2

4

6

8

10

12

14

16

0 1 2 3 4

Load

s (kN

)

Deflection (mm)


(a) 075120591max rarr 080120591max(5119889119887)

0

5

10

15

20

25

0 1 2 3 4

Load

s (kN

)

Deflection (mm)


(b) 075120591max rarr 080120591max(15119889119887)


0

2

4

6

8

10

12

14

16

Load

s (kN

)


(c) 080120591max rarr 075120591max(5119889119887)


0

5

10

15

20

25Lo

ad (k

N)


(d) 080120591max rarr 075120591max(15119889119887)


0

2

4

6

8

10

12

14

16

Load

s (kN

)




0

5

10

15

20

25

Load

s (kN

)







0

01

02

03

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)


5db_07515db_0755db_08

15db_085db_09

(a)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)




(b)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)



(c)



Load case 1198631

1198632

1198633

sum119863119894

5119889119887


15119889119887



119887and 10119889




119887and 10119889








Reduction of

Residual slip

Slip

Bond

ing

stren

gth

Fatigue test

Static test








119878119887 frp

=

1

2



(3)


119887and 10119889

119887specimens

119878119887 frp for the 5119889

119887and 10119889





7 Conclusions










Acknowledgments



References























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




P

C = 30

150

200PVC500

1300

100

50


50050

LVDT

Concrete beam

GFRP bar



C

T

j

P

lb1 lb2 lb3

Bonded

500mm

a = 550mm

180mm

170mm

30mm



119887) are


1198871= 5119889

119887(45mm) 119897

1198872= 10119889

119887(90mm) and

1198971198873= 15119889

119887(135mm) where 119889











5119889119887

1634 1263 01931511 906 0125

10119889119887

11 761 01351222 688 0168

15119889119887

959 577 0050807 603 0060

0

2

4

6

8

10

12

14

16

0 1 2 3 4

Flex

ural

bon

d str

engt

h (M

Pa)



(a)

0

2

4

6

8

10

12

14

16

0 1 2 3 4

Flex

ural

bon

d str

engt

h (M

Pa)



(b)

















Number ofcycles


(MPa)

Failure mode

5119889119887

(45mm) 151

70758090

114122130147

0175mdashmdashmdash

20000001516231292683804

105mdashmdashmdash

Plowast

10119889119887

(90mm) 102 7080

7788

0083mdash

200000081063

64mdash Plowast

15119889119887

(135mm) 75

60758085

48607277


20000001981582193972114413

39mdashmdashmdash

CSlowastlowast


5 10 152

3

4

5

6

7

376676 372344

466044

152

116

882

0

4

8

12

16

20

Tota

l wor

k en

ergy

(Nm

m)

Max

bon

d str

engt

h (M

Pa)

times104



0

5

10

15

20

25

30

35

0 50 100 150 200 250 300 350

Flex

ural

bon

d str

engt

h (M

Pa)

Bond length (mm)



ACI 440 1R-03










119887and 10119889



119887and 10119889





0

2

4

6

8

10

12

14

16

0 01 02 03 04 05 06 07 08 09 1

Bond

ing

stren

gth

(MPa

)

Slip (mm)











119887


0

2

4

6

8

10

12

14

16

0 01 02 03 04 05 06

Bond

ing

stren

gth

(MPa

)

Slip (mm)







119887









119887and 0083mm for 10119889



119887and 10119889

119887specimens


119887and 10119889






5119889119887

minus265 ln(119909) + 11007 68010119889119887

minus3119 ln(119909) + 11526 650

50

60

70

80

90

100

Stre

ss le

vel (

)

1 102 104 106 108



Fatigue life (Nf)

15db (135mm)10db (90mm)5db (45mm)

10db and 15db)





119887and 15119889

119887














119887


119891119873119891)


119863 =

119896

sum

119894=1

119899119894

119873119894

(2)








0

2

4

6

8

10

12

14

16

0 1 2 3 4

Load

s (kN

)

Deflection (mm)


(a) 075120591max rarr 080120591max(5119889119887)

0

5

10

15

20

25

0 1 2 3 4

Load

s (kN

)

Deflection (mm)


(b) 075120591max rarr 080120591max(15119889119887)


0

2

4

6

8

10

12

14

16

Load

s (kN

)


(c) 080120591max rarr 075120591max(5119889119887)


0

5

10

15

20

25Lo

ad (k

N)


(d) 080120591max rarr 075120591max(15119889119887)


0

2

4

6

8

10

12

14

16

Load

s (kN

)




0

5

10

15

20

25

Load

s (kN

)







0

01

02

03

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)


5db_07515db_0755db_08

15db_085db_09

(a)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)




(b)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)



(c)



Load case 1198631

1198632

1198633

sum119863119894

5119889119887


15119889119887



119887and 10119889




119887and 10119889








Reduction of

Residual slip

Slip

Bond

ing

stren

gth

Fatigue test

Static test








119878119887 frp

=

1

2



(3)


119887and 10119889

119887specimens

119878119887 frp for the 5119889

119887and 10119889





7 Conclusions










Acknowledgments



References























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






5119889119887

1634 1263 01931511 906 0125

10119889119887

11 761 01351222 688 0168

15119889119887

959 577 0050807 603 0060

0

2

4

6

8

10

12

14

16

0 1 2 3 4

Flex

ural

bon

d str

engt

h (M

Pa)



(a)

0

2

4

6

8

10

12

14

16

0 1 2 3 4

Flex

ural

bon

d str

engt

h (M

Pa)



(b)

















Number ofcycles


(MPa)

Failure mode

5119889119887

(45mm) 151

70758090

114122130147

0175mdashmdashmdash

20000001516231292683804

105mdashmdashmdash

Plowast

10119889119887

(90mm) 102 7080

7788

0083mdash

200000081063

64mdash Plowast

15119889119887

(135mm) 75

60758085

48607277


20000001981582193972114413

39mdashmdashmdash

CSlowastlowast


5 10 152

3

4

5

6

7

376676 372344

466044

152

116

882

0

4

8

12

16

20

Tota

l wor

k en

ergy

(Nm

m)

Max

bon

d str

engt

h (M

Pa)

times104



0

5

10

15

20

25

30

35

0 50 100 150 200 250 300 350

Flex

ural

bon

d str

engt

h (M

Pa)

Bond length (mm)



ACI 440 1R-03










119887and 10119889



119887and 10119889





0

2

4

6

8

10

12

14

16

0 01 02 03 04 05 06 07 08 09 1

Bond

ing

stren

gth

(MPa

)

Slip (mm)











119887


0

2

4

6

8

10

12

14

16

0 01 02 03 04 05 06

Bond

ing

stren

gth

(MPa

)

Slip (mm)







119887









119887and 0083mm for 10119889



119887and 10119889

119887specimens


119887and 10119889






5119889119887

minus265 ln(119909) + 11007 68010119889119887

minus3119 ln(119909) + 11526 650

50

60

70

80

90

100

Stre

ss le

vel (

)

1 102 104 106 108



Fatigue life (Nf)

15db (135mm)10db (90mm)5db (45mm)

10db and 15db)





119887and 15119889

119887














119887


119891119873119891)


119863 =

119896

sum

119894=1

119899119894

119873119894

(2)








0

2

4

6

8

10

12

14

16

0 1 2 3 4

Load

s (kN

)

Deflection (mm)


(a) 075120591max rarr 080120591max(5119889119887)

0

5

10

15

20

25

0 1 2 3 4

Load

s (kN

)

Deflection (mm)


(b) 075120591max rarr 080120591max(15119889119887)


0

2

4

6

8

10

12

14

16

Load

s (kN

)


(c) 080120591max rarr 075120591max(5119889119887)


0

5

10

15

20

25Lo

ad (k

N)


(d) 080120591max rarr 075120591max(15119889119887)


0

2

4

6

8

10

12

14

16

Load

s (kN

)




0

5

10

15

20

25

Load

s (kN

)







0

01

02

03

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)


5db_07515db_0755db_08

15db_085db_09

(a)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)




(b)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)



(c)



Load case 1198631

1198632

1198633

sum119863119894

5119889119887


15119889119887



119887and 10119889




119887and 10119889








Reduction of

Residual slip

Slip

Bond

ing

stren

gth

Fatigue test

Static test








119878119887 frp

=

1

2



(3)


119887and 10119889

119887specimens

119878119887 frp for the 5119889

119887and 10119889





7 Conclusions










Acknowledgments



References























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials









Number ofcycles


(MPa)

Failure mode

5119889119887

(45mm) 151

70758090

114122130147

0175mdashmdashmdash

20000001516231292683804

105mdashmdashmdash

Plowast

10119889119887

(90mm) 102 7080

7788

0083mdash

200000081063

64mdash Plowast

15119889119887

(135mm) 75

60758085

48607277


20000001981582193972114413

39mdashmdashmdash

CSlowastlowast


5 10 152

3

4

5

6

7

376676 372344

466044

152

116

882

0

4

8

12

16

20

Tota

l wor

k en

ergy

(Nm

m)

Max

bon

d str

engt

h (M

Pa)

times104



0

5

10

15

20

25

30

35

0 50 100 150 200 250 300 350

Flex

ural

bon

d str

engt

h (M

Pa)

Bond length (mm)



ACI 440 1R-03










119887and 10119889



119887and 10119889





0

2

4

6

8

10

12

14

16

0 01 02 03 04 05 06 07 08 09 1

Bond

ing

stren

gth

(MPa

)

Slip (mm)











119887


0

2

4

6

8

10

12

14

16

0 01 02 03 04 05 06

Bond

ing

stren

gth

(MPa

)

Slip (mm)







119887









119887and 0083mm for 10119889



119887and 10119889

119887specimens


119887and 10119889






5119889119887

minus265 ln(119909) + 11007 68010119889119887

minus3119 ln(119909) + 11526 650

50

60

70

80

90

100

Stre

ss le

vel (

)

1 102 104 106 108



Fatigue life (Nf)

15db (135mm)10db (90mm)5db (45mm)

10db and 15db)





119887and 15119889

119887














119887


119891119873119891)


119863 =

119896

sum

119894=1

119899119894

119873119894

(2)








0

2

4

6

8

10

12

14

16

0 1 2 3 4

Load

s (kN

)

Deflection (mm)


(a) 075120591max rarr 080120591max(5119889119887)

0

5

10

15

20

25

0 1 2 3 4

Load

s (kN

)

Deflection (mm)


(b) 075120591max rarr 080120591max(15119889119887)


0

2

4

6

8

10

12

14

16

Load

s (kN

)


(c) 080120591max rarr 075120591max(5119889119887)


0

5

10

15

20

25Lo

ad (k

N)


(d) 080120591max rarr 075120591max(15119889119887)


0

2

4

6

8

10

12

14

16

Load

s (kN

)




0

5

10

15

20

25

Load

s (kN

)







0

01

02

03

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)


5db_07515db_0755db_08

15db_085db_09

(a)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)




(b)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)



(c)



Load case 1198631

1198632

1198633

sum119863119894

5119889119887


15119889119887



119887and 10119889




119887and 10119889








Reduction of

Residual slip

Slip

Bond

ing

stren

gth

Fatigue test

Static test








119878119887 frp

=

1

2



(3)


119887and 10119889

119887specimens

119878119887 frp for the 5119889

119887and 10119889





7 Conclusions










Acknowledgments



References























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





0

2

4

6

8

10

12

14

16

0 01 02 03 04 05 06 07 08 09 1

Bond

ing

stren

gth

(MPa

)

Slip (mm)











119887


0

2

4

6

8

10

12

14

16

0 01 02 03 04 05 06

Bond

ing

stren

gth

(MPa

)

Slip (mm)







119887









119887and 0083mm for 10119889



119887and 10119889

119887specimens


119887and 10119889






5119889119887

minus265 ln(119909) + 11007 68010119889119887

minus3119 ln(119909) + 11526 650

50

60

70

80

90

100

Stre

ss le

vel (

)

1 102 104 106 108



Fatigue life (Nf)

15db (135mm)10db (90mm)5db (45mm)

10db and 15db)





119887and 15119889

119887














119887


119891119873119891)


119863 =

119896

sum

119894=1

119899119894

119873119894

(2)








0

2

4

6

8

10

12

14

16

0 1 2 3 4

Load

s (kN

)

Deflection (mm)


(a) 075120591max rarr 080120591max(5119889119887)

0

5

10

15

20

25

0 1 2 3 4

Load

s (kN

)

Deflection (mm)


(b) 075120591max rarr 080120591max(15119889119887)


0

2

4

6

8

10

12

14

16

Load

s (kN

)


(c) 080120591max rarr 075120591max(5119889119887)


0

5

10

15

20

25Lo

ad (k

N)


(d) 080120591max rarr 075120591max(15119889119887)


0

2

4

6

8

10

12

14

16

Load

s (kN

)




0

5

10

15

20

25

Load

s (kN

)







0

01

02

03

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)


5db_07515db_0755db_08

15db_085db_09

(a)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)




(b)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)



(c)



Load case 1198631

1198632

1198633

sum119863119894

5119889119887


15119889119887



119887and 10119889




119887and 10119889








Reduction of

Residual slip

Slip

Bond

ing

stren

gth

Fatigue test

Static test








119878119887 frp

=

1

2



(3)


119887and 10119889

119887specimens

119878119887 frp for the 5119889

119887and 10119889





7 Conclusions










Acknowledgments



References























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






5119889119887

minus265 ln(119909) + 11007 68010119889119887

minus3119 ln(119909) + 11526 650

50

60

70

80

90

100

Stre

ss le

vel (

)

1 102 104 106 108



Fatigue life (Nf)

15db (135mm)10db (90mm)5db (45mm)

10db and 15db)





119887and 15119889

119887














119887


119891119873119891)


119863 =

119896

sum

119894=1

119899119894

119873119894

(2)








0

2

4

6

8

10

12

14

16

0 1 2 3 4

Load

s (kN

)

Deflection (mm)


(a) 075120591max rarr 080120591max(5119889119887)

0

5

10

15

20

25

0 1 2 3 4

Load

s (kN

)

Deflection (mm)


(b) 075120591max rarr 080120591max(15119889119887)


0

2

4

6

8

10

12

14

16

Load

s (kN

)


(c) 080120591max rarr 075120591max(5119889119887)


0

5

10

15

20

25Lo

ad (k

N)


(d) 080120591max rarr 075120591max(15119889119887)


0

2

4

6

8

10

12

14

16

Load

s (kN

)




0

5

10

15

20

25

Load

s (kN

)







0

01

02

03

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)


5db_07515db_0755db_08

15db_085db_09

(a)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)




(b)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)



(c)



Load case 1198631

1198632

1198633

sum119863119894

5119889119887


15119889119887



119887and 10119889




119887and 10119889








Reduction of

Residual slip

Slip

Bond

ing

stren

gth

Fatigue test

Static test








119878119887 frp

=

1

2



(3)


119887and 10119889

119887specimens

119878119887 frp for the 5119889

119887and 10119889





7 Conclusions










Acknowledgments



References























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0

2

4

6

8

10

12

14

16

0 1 2 3 4

Load

s (kN

)

Deflection (mm)


(a) 075120591max rarr 080120591max(5119889119887)

0

5

10

15

20

25

0 1 2 3 4

Load

s (kN

)

Deflection (mm)


(b) 075120591max rarr 080120591max(15119889119887)


0

2

4

6

8

10

12

14

16

Load

s (kN

)


(c) 080120591max rarr 075120591max(5119889119887)


0

5

10

15

20

25Lo

ad (k

N)


(d) 080120591max rarr 075120591max(15119889119887)


0

2

4

6

8

10

12

14

16

Load

s (kN

)




0

5

10

15

20

25

Load

s (kN

)







0

01

02

03

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)


5db_07515db_0755db_08

15db_085db_09

(a)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)




(b)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)



(c)



Load case 1198631

1198632

1198633

sum119863119894

5119889119887


15119889119887



119887and 10119889




119887and 10119889








Reduction of

Residual slip

Slip

Bond

ing

stren

gth

Fatigue test

Static test








119878119887 frp

=

1

2



(3)


119887and 10119889

119887specimens

119878119887 frp for the 5119889

119887and 10119889





7 Conclusions










Acknowledgments



References























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






0

01

02

03

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)


5db_07515db_0755db_08

15db_085db_09

(a)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)




(b)

00102030405

0 02 04 06 08 1Unl

oade

d en

d sli

p (m

m)



(c)



Load case 1198631

1198632

1198633

sum119863119894

5119889119887


15119889119887



119887and 10119889




119887and 10119889








Reduction of

Residual slip

Slip

Bond

ing

stren

gth

Fatigue test

Static test








119878119887 frp

=

1

2



(3)


119887and 10119889

119887specimens

119878119887 frp for the 5119889

119887and 10119889





7 Conclusions










Acknowledgments



References























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Reduction of

Residual slip

Slip

Bond

ing

stren

gth

Fatigue test

Static test








119878119887 frp

=

1

2



(3)


119887and 10119889

119887specimens

119878119887 frp for the 5119889

119887and 10119889





7 Conclusions










Acknowledgments



References























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




References























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



research article experimental assessment on the flexural

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