ContactandNoncontactUltrasonicNondestructiveTestin...

Research ArticleContact and Noncontact Ultrasonic Nondestructive Test inReinforced Concrete Beam

Jason Maximino C Ongpeng 1 Andres Winston C Oreta2 and Sohichi Hirose3

1Associate Professor De La Salle University 2401 Taft Avenue 1004 Manila Philippines2Professor De La Salle University 2401 Taft Avenue 0922 Manila Philippines3Professor Tokyo Institute of Technology W8-22 2-12-1 Ookayama Meguro-ku Tokyo 152-8552 Japan

Correspondence should be addressed to Jason Maximino C Ongpeng jasonongpengdlsueduph

Received 26 July 2018 Revised 4 October 2018 Accepted 16 October 2018 Published 1 November 2018

Academic Editor Flavio Stochino

Copyright copy 2018 Jason Maximino C Ongpeng et al is is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in anymedium provided the original work isproperly cited

Contact-type ultrasonic test is commonly used in construction industry where gel-couplant is applied to the material being testedand the transducers to assure that wave propagation will travel through without any air gaps However this method hasdisadvantages since surface preparation is considered prior to testing Another method of testing without the worry of air gapsthat causes scattering of waves before it reaches the medium is the use of the noncontact ultrasonic test In particular the air-coupled ultrasonic test is done in this paper for reinforced concrete beams Sixteen plain concrete cube specimens under thecompression test and six reinforced concrete beam specimens under the four-point bending test are made with water-cement ratioof 40 and 60 e plain concrete cubes are investigated to establish the relationship of the contact ultrasonic test and loadAdded parameters are considered to investigate the sensitivity of the contact and noncontact ultrasonic test in reinforced concretebeams ese are ultrasonic wave path and the neutral axis index It shows that the higher water-cement ratio produces goodsensitivity in the noncontact ultrasonic test since it produces more cracks on the tension face Lower water-cement ratio givesgood sensitivity with load for the contact ultrasonic test since it has its ultrasonic wave path passing through the concreteexperiencing compression In addition the neutral axis index for a member subjected to bending is an important factor inassessing the sensitivity of both contact and noncontact ultrasonic test

1 Introduction

Structures need to be assessed using structural health mon-itoring techniques especially for the predominant materialslike reinforced concrete Concrete comprises water cementsand and aggregates with some admixtures that bond to-gether to form a porous materialis heterogeneous materialis very complex due to its nonlinear characteristics Concreteproves to be a challenge in the field of nondestructivemethodscompared to metal

One effective way of testing materials is the use of theultrasonic test Combination of the ultrasonic test usingultrasonic pulse velocity (UPV) and rebound hammer isintroduced to test on site strength of concrete [1] Testcombinations with UPV to improve the prediction ofstrength of concrete are still limited due to its insensitivity

to the changes in load [2] e conventional ultrasonic testuses transducers with gel-couplant applied on the materialto assure that the ultrasonic wave in contact with thematerial being tested will have no air gaps Presence of airgaps in the contact-type ultrasonic test is a disadvantagesince it can scatter the wave propagation that can arrive atlow-sensitivity measurements In actual field inspectionthe contact ultrasonic test with gel-couplant is troublesomedue to the accessibility of inspector to the concrete surfacebeing investigated

Another way of testing concrete without considering theair gaps is the use of the noncontact ultrasonic test Inparticular the air-coupled ultrasonic test is a good exampleto eliminate the use of gel-couplant which is a significantfactor in data collection and analysis Air-coupled sensorswere developed in the 1970s and were mainly used for

HindawiAdvances in Civil EngineeringVolume 2018 Article ID 5783175 10 pageshttpsdoiorg10115520185783175

inspection of wood and quality control of paper art objectsand advanced composite materials used in the aerospaceindustry [3] Quality tests in paper focused on sound dis-persion and attenuation and estimation of its surfaceroughness can be monitored [4 5] In construction buildingmaterials this method is now being developed for noncontactdetection of surface waves in concrete [3] Additionally theimpact response test in the composite material using theC-scan technique is also being developed in diagnosingconcrete [6ndash8] Various studies including wooden panelpainting investigation and refraction including damping oftimber laminates are also done in previous researches [9 10]

Air-coupled ultrasonic test is gaining popularity andadvancement Waves in metals and composite materialshave been successfully detected through the application ofsensors having frequency of 50 kHz to 1MHz In testingconcrete a flat frequency response below 100 kHz is idealLow-frequency range sensors detect leaky waves in concreteIt is also proven that the use of air-coupled sensors is notsensitive to surface conditions in concrete and is sensitive tothe existence of cracks as waves propagate across it [3] It canalso assess material nonlinearity [11] including carbonationinside concrete materials [12] As the noncontact testmethod enables fast scanning of large structures the am-plitude information that is obtained is dependable andconsistent when it is transmitted to the solid material [13]

e received time-domain waveform is the commondata retrieved in this test e parameters that are measuredin time-domain waveform are time of arrival and peak topeak amplitude Time of arrival of an ultrasonic wavepassing through a dense medium should be smaller than theporous or damaged material Peak to peak amplitude issensitive to scattering of ultrasonic waves passing throughthe medium In addition received time-domain waveform isconverted to frequency-domain waveform using fast Fouriertransform e parameters under frequency-domainwaveform consist of fundamental amplitude and higherharmonic amplitudes Previous research show that plainconcrete cubes with different load-loading patterns greatlyinfluences the higher harmonics parameters [14] Com-plexity in the damage level for concrete is recognized whendifferent sizes of aggregates inside concrete are present [15]From references the UPV test is convenient in detectingflaws like corrosion inside concrete [16] but it is insensitiveto the internal damage In addition for plain concrete cubesthe correlation of ultrasonic parameters to internal damagerepresented by changes in load was done using artificialneural network model and it indicated that UPV has veryweak correlation compared to peak to peak amplitude of thetime-domain waveform [17] Investigation of reinforcedconcrete beams was considered using the artificial neuralnetwork model e results showed that the contact-typeultrasonic test using peak to peak amplitude as a parameterto detect damage was classified as long- and short-rangesensitivity for WC40 and WC60 respectively Long- andshort-range sensitivity from the model developed can detectdamage more than 20 and less than 20 respectively [18]

In this paper peak to peak amplitude of time-domainwaveform is used as a parameter to measure the damage

Decrease in peak to peak amplitude is evident when there isa scattering of the ultrasonic wave upon loading e ex-perimental test involved two test methods for both water-cement ratio (WC) 60 and 40ese are the compression testof sixteen cube specimens of size 150mm on each side andsix concrete beams under the four-point bending test ecompression test is established to show the sensitivity of thepeak to peak amplitude using the contact ultrasonic testwhile the four-point bending test is performed to show therelationship of the reinforced concrete beamrsquos load neutralaxis index and the peak to peak amplitude for both thecontact and noncontact ultrasonic test

2 Plain Concrete Cubes under Compression

Sixteen concrete cubes were casted having size of 150mm times

150mm times 150mm Varying water-cement ratios of WC40and WC60 were used to investigate the effect of the test withdifferent water-cement ratios e maximum size of aggre-gates used was 20mm and the ratio of sand-total aggregatewas 45 Table 1 shows the content of the ingredients Auniversal testing machine was used and each specimen wassubjected to the compression test at their mature age of 28days e compressive strength of WC40 and WC60 wastested prior to the experiment and resulted to characteristicstrength of 53MPa and 40MPa respectively e rate ofloadingunloading was 05 kN per second with the loadpattern (Figure 1) Four loading branches were consideredhaving a percent load of 0 to 20 0 to 40 0 to 60and 0 to 100 respectively

Specimens were tested by uniaxial compressive load(Figure 2(a)) Pitch-catch ultrasonic test was used to recordthe time-domain waveforms in each loading or unloadingstep A high-gain broadband receiver and two transducersconnected to the oscilloscope with tone-burst pulser wereused in the setup e supplied voltage was set at 1800 voltswith the sine wave having 10 cycles at 100 kHz In additionthe low-pass filter was set at 3MHz and the high-pass filterwas set at 50 kHz with an input impedance of 50Ω Directtransmission was implemented in the wave path of theultrasonic wave from the transmitting to the receivingtransducers (Figure 2(b)) is wave path was passingthrough the concrete experiencing compression etransmitting and receiving transducers were carefullyaligned centered and bonded to the concrete cubes with gel-couplants e transmitting transducer had its generatingfrequency at 100 kHz that sent signal across the specimene receiving transducer on the contrary had 200 kHzfrequency and was placed on the opposite face is fre-quency of transducers proved to be effective in measuringinternal damage inside the concrete material [14 15]

Time-domain waveforms were recorded for the firstloading branch of 0 20 40 60 and 80 (Figure 3) Itwas observed that the peak to peak amplitude decreases withrespect to increasing load A damage level assessment is usedin this paper by solving its normalized peak to peak am-plitude in decibels as seen in Equation (1) It followed theconcepts in electrical circuits which dissipated power fromone state to the other is parameter is used to measure

2 Advances in Civil Engineering

damage presented when amplitudes decrease with respectto load [14 15]

normalized peak to peak amplitude(dB) 20lowast logA1A0

1113874 1113875

(1)

where A1 is the peak to peak amplitude at any load (volts)and

A0 is the maximum peak to peak amplitude throughoutthe test (volts)

e average normalized peak to peak amplitude ofWC 40and 60 is calculated (Figure 4) e damage level is inverselyproportional to the load for both WCs High WC produceslarger magnitude of normalized peak to peak amplitude dueto the air voids in thematerial that led to wide scattering of theultrasonic wave when it passes the mediume damage levelfor each loading branch L1 to L4 is recorded and compared(Figure 5) e magnitude of the damage is proportional tothe load increase in the concrete cubes e results gave goodagreement for plain concrete when subjected to the ultrasonictest using peak to peak amplitude as a parameter to measurethe load it experiences under direct transmission with themedium under compression

3 Reinforced Concrete Beams under theFour-Point Bending Test

ere were six 100mm times 100mm times 400mm single-reinforced concrete beams specimen with WC of 60 and40 e reinforcing bar used was 9mm in diameter witha yield strength of 400MPa and was placed at the bottom ofthe beam with a concrete cover of 10mm (Figure 6) econcrete designmix was the same as the plain concrete cubesin the previous section A notch of 3mm was made at themidspan of the bottom beamis was to make sure that the

crack formationmonitored by the air-coupled ultrasonic testwas locally focused at the concrete surface in tension euse of 9mm reinforcing steel bar parallel to the position ofthe transducers were assumed to be negligible In the UPVtest with good quality concrete the presence of the 12mmdiameter bar is insignificant [19]

Four-point bending test was done together with the air-coupled ultrasonic test e air-coupled ultrasonic trans-ducers (the transmitter and receiver) were oriented 8 degreesfrom the vertical axis and were focused on the midspantension side where the bendingtension cracks occurredeair-coupled ultrasonic test was focused on the inverted setupusing the Japan Probe JPR-660C with the 200 kHz air-coupled transmitter and receiver Maximum voltage wasset at 600V with the burst wave of 10 waves

It was made having an inverted layout (Figure 7) toproperly place the air-coupled transducers upright along themidspan of the beam where tension crack occurred Locationof the strain gauges was placed at midspan and longitudinallyalong the beam positioned at the top and the bottom faces ofthe beame collection and analysis of data after the test wasshifted to the upright position where the presence of momentin the beam was in the positive direction

Loading and unloading paths were made to relate thebehavior of the contact and noncontact ultrasonic test resultsrsquopeak to peak amplitude with the load and the changes in itsneutral axis index (Figure 8) ere were 5 cycles of repeatedload for 20 40 and 60 followed lastly by the final loaduntil failure e air-coupled ultrasonic transducers (thetransmitter and receiver) were oriented 8 degrees from thevertical axis and were focused on the midspan tension sidewhere the bendingtension cracks occurred (Figure 9) eair-coupled ultrasonic test was focused on the inverted setupwhile the gel-coupled ultrasonic tested was oriented longi-tudinally under direct transmission (Figure 10)

e average normalized peak to peak amplitude of thethree beams with WC60 is calculated using Equation (1)(Figures 11 and 12) For the noncontact ultrasonic test theinitial from step load 1 and 2 behaved inconsistent due to theinitial state of the concrete before it stabilizes opening andclosing of cracks according to the load applied It can benoticed that the normalized peak to peak amplitude issensitive to load especially from the step loads 31 to the endwhere it experiences loading and unloading from 0 to 60 ofload Incremental damage is seen to be consistent in eachcycle of loading and unloading

For the contact ultrasonic test with direct transmissionalong its length the deviation of the normalized peak to peakshowed sensitivity for load less than 40 However it can benoticed that the measurement was not responsive to loadsince there were many cracks that caused a lot of scattering

Table 1 Design mix of concrete

Type Maximum size of gravel (mm) WC ()Unit quantity (kgm3)

Water Cement Sand Gravel Water-reducing agentWC40 20 40 169 422 702 1039 084WC60 60 175 291 812 1021 058

0

20

40

60

80

100

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Perc

ent l

oad

Step load

Loading branches 4th

3rd

1st 2nd

Figure 1 Multiple loadingunloading patterns for plain concreteWC40 and WC60

Advances in Civil Engineering 3

inside the concrete after step load 13 (40 or more loads)Not responsive to load means that there was no significantresistance experienced in concrete or the fluctuations had nosignificant changes which is less than 15 dB from the un-damaged state

e behavior of damage for the contact and noncontactultrasonic test is seen in Figure 12 e contact ultrasonic

Transmitter100 kHz

Receiver200 kHz

Load

Rigid base

Compressive (loading-unloading) testsetup

Pulserreceiver

(a)

Wave path

Receiver15

1015

00 510

1515

Transmitter

10

5z (cm

)

0

y (cm) x (cm)

(b)

Figure 2 (a) Compressive testing procedure by loading and unloading for plain concrete withWC40 andWC60 (b) concrete cube showingultrasonic wave path represented by a cylinder in direct transmission

08

Am

plitu

de (v

olts)

060402

0ndash02ndash04ndash06ndash08

Time

Peak to peakamplitude

Load at 0Load at 20Load at 40

Load at 60Load at 80

Figure 3 Time-domain waves showing peak to peak amplitude

ndash30

ndash20

ndash10

0

0

20

40

60

80

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Paek

to p

eak

ampl

itude

(dB)

Perc

ent l

oad

Step load

LoadWC40WC60

Figure 4 Total damage represented by normalized peak to peakamplitude

WC60 WC40L1 ndash5255749557 ndash3721205346L2 ndash113848762 ndash1052498208L3 ndash1717037587 ndash1104784436L4 ndash2780561106 ndash2053279781

ndash30ndash25ndash20ndash15ndash10

ndash50

Total damage (dB)

Figure 5 Total damage in each loading branch for plain concretecubes under compression

9mm diameter bar

100mm 400mm

Cover = 10mm100mm

Front elevation Side elevation

Figure 6 Reinforced concrete beamrsquos front and side elevation

BeamP2 P2

Oil hydraulic pump

Figure 7 Reinforced concrete beam with WC40 and WC60 underthe four-point bending test


test behaved consistent with Section 2 for plain concretecubes whereas the normalized peak to peak amplitudedecreases as load increases On the other hand the non-contact ultrasonic test was not responsive to load since therewere many cracks that caused a lot of scattering inside theconcrete after step load 13 (40 or more loads)

e complexity of the results (Figures 11 and 12) isbrought about factors different from the plain concrete cubecompression test results in the previous section In theuniaxial compression test of concrete specimens experi-mental results from literature showed that the ultrasonicpulse wave varied with the direction of compressive loadIt was found out that UPV increases when there is an in-crease in compressive load for transducers placed parallel tothe compressive load due to the acoustoelastic effect Re-duction of UPV occurred when the load is perpendicularto the transducersrsquo placement [20] Using the noncontactultrasonic test an increase in Rayleigh phase velocity was

observed for concrete and mortar surfaces with the re-duction of microcracks [21] ere are limited studies in theapplication of the ultrasonic test in reinforced beamswhether it may focus on time-domain or frequency-domainwaveforms e flexural behavior of concrete is complexsince it comprises tension and compression zones withvarying neutral axis index locations In previous workconcrete slabs were tested using the four-point bending testIt was found out that the amplitude of the ultrasonic wavedecreases in tension face and increases in compression face[22] In addition the UPV values increased when thebending load in the prestressed beam increases [23] In theplain concrete cube the contact ultrasonic test is done withthe whole specimen experiencing compression while thereinforced concrete beam experiences both compressionresisted by concrete and tension resisted by the reinforcingbar With this another parameter is introduced the neutralaxis index is parameter is promising in structural healthmonitoring where it is considered to be a sensitive universalparameter [24] In determining the neutral axis index lo-cation with respect to changes in load in this paper therecorded tensile and compressive strain is considered at themidspan of the beam Diagram showing the cross sectionsample strain diagram at a particular step load and itscorresponding stress diagram are considered (Figure 13)

is location of the neutral axis index is dynamic due tothe changes in load that influences the strain at the top andbottom of the beam during the step loads in the experimente dynamic neutral axis index is computed using Equation(2) is location of the neutral axis index ldquoyrdquo is correlatedwith the theory on the elastic design of reinforced concrete Inthis study the actual neutral axis index in the experimentationwas very difficult to measure hence it was called the ldquoneutralaxis indexrdquo with the same formula shown in Equation (2)

y εchεt minus εc( 1113857

(2)

where y is the neutral axis index in mmh is the height of the beam in mmεc is the average strain at the midpoint top surface in

compression andεt is the average strain at midpoint bottom surface in

tension

0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Perc

ent l

oad

Step load

L3

L2

L1

Figure 8 Multiple loadingunloading patterns for the reinforced concrete beam with WC40 and WC60

8 degrees from vertical

Figure 9 Air-coupled ultrasonic test setup

Support

P2 P2

TransmitterAir-coupled transducers

TransmitterMidspan crack tension

Gel-coupled transducers

Receiver

ReceiverSupport

Figure 10 Contact and noncontact ultrasonic test performed inthe reinforced concrete beam


e recorded strain data was smoothened and processedto determine the minimum and maximum peaks corre-sponding to each step load Figure 14 shows the strain data ofspecimens 1 2 and 3 with WC60 Specimens 1 and 2 wereconsistent with close standard deviation while specimen 3had minimal changes in its strain gauges at the latter loadingbranches is was due to the limitation of using one straingauge at the middle for each of the surfaces at the top andbottom where crack formation led to different patterns fromone specimen to another Furthermore average of straindata was made to investigate the difference between WC40

and WC60 as seen in Figure 15 e average strain intension and compression of WC60 was greater than that ofWC40 e average tensile strain of WC40 produced rela-tively low values is low value of average tensile strain atthe beginning had experienced abrupt increase after itreached 60 of load where sudden crack formation wasnoticed visually during the test

ere were two theories to verify the behavior of theneutral axis index against the load (1) the neutral axis indexwhen the tension side of the concrete starts to crackcomputed y 49mm (2) the neutral axis index when the

ndash400

ndash300

ndash200

ndash100

000

0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Peak

to p

eak

ampl

itude

(dB)

Perc

ent l

oad

Step load

Load ()WC60 noncontact (dB)WC60 contact (dB)

Figure 11 Average total damage represented by normalized peak to peak amplitude for WC60

ndash800ndash700ndash600ndash500ndash400ndash300ndash200ndash100000

0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Peak

to p

eak

ampl

itude

(dB)

Perc

ent l

oad

Step load



h d

(a) (b) (c)

Neutral axis

εs

εc

y

bAs

Fst

Fcc Mo

εt

Figure 13 Neutral axis index across (a) cross section of the beam (b) strain diagram and (c) stress diagram


concrete below is redundant and only the reinforcing barresists the moment in tension computed y 23mm(Figure 16(a))

In a reference it was assumed that the P wave or ul-trasonic wave was perpendicular from the transducerrsquossurface [25] One factor that also affects the wave propa-gation is the orientation of fibers is is important in de-termining the wave propagation in terms of wavefronts andray path It was found out that for isotropic materials theray paths are collinear from the transmitter to the receiverwith wavefronts perpendicular from the ray paths Differentbehaviors occurred in the orthotropic material whereacoustic wave propagation follows a curved ray path [26] Inthis paper the wave path was assumed to be the wavepropagation from the transmitter to the receiver of ray pathsand wavefronts that are inside the volume generated by thearea of contact of the transducers from the transmission to

the receiver Any reflection and refraction outside the cy-lindrical volume was assumed to have a negligible effect onthe data collection and analysis

ewave path for theWC60 beam of the contact ultrasonictest was shown as the circular region covered by the wave pathwhen the neutral axis indexwas 23mm (Figure 16(b)) It can benoted that during the L1 loadingunloading branches thewavepath passed through the compressive zone and hence sen-sitivity on the normalized peak to peak amplitude was expe-rienced However in the L2 loadingunloading branchnormalized peak to peak amplitude was not sensitive due tolower concrete quality where presence of more air voids wasexperienced after step load 13 (40 or more load) Lastlyduring the L3 loadingunloading branches normalized peak topeak amplitude was not sensitive due to low concrete qualityand that the ultrasonic wave path did not pass through thecompression zone Further investigation is recommended

00000

00100

00200

00300

00400

00500

00600

ndash00060

ndash00050

ndash00040

ndash00030

ndash00020

ndash00010

00000

Botto

m fi

ber s

trai

n (m

m)

Top

fiber

stra

in (m

m)

Time

Specimen 1 compressionSpecimen 2 compressionSpecimen 3 compression

Specimen 1 tensionSpecimen 2 tensionSpecimen 3 tension

L1L2

L3

Figure 14 Strain data of specimens 1 2 and 3 with WC60

00000

00050

00100

00150

00200

00250

ndash00030

ndash00025

ndash00020

ndash00015

ndash00010

ndash00005

00000

Tens

ile st

rain

(mm

)

Com

pres

sive s

trai

n (m

m)

Time

Average strainin compression WC60Average strainin tension WC60


Figure 15 Average strain in tension and compression for WC60 and WC40


100

WC60 abrupt NA change

Neu

tral

axis

at m

idsp

an (m

m)

ndash10

0

ndash20

ndash30

ndash40

ndash50

ndash60

ndash70

ndash80

ndash90

ndash100

90

Perc

ent l

oad

80

70

60

50

40

30

20

10

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Step load

(a) (b)

39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71

y = 49mm when concrete starts to crack

Ultrasonic wave path

Width

Cracks9mm diameter bar

Load ()WC60

y = 23mm when concretebelow NA does not resist tension

Figure 16 (a) Changes in the neutral axis index according to load forWC60 (b) cross section of the beam showing the ultrasonic wave pathfor WC60

100

WC40 abrupt NA changeN

eutr

al ax

is at

mid

span

(mm

)ndash10

0

ndash20

ndash30

ndash40

ndash50

ndash60

ndash70

ndash80

ndash90

ndash100

90

Perc

ent l

oad

80

70

60

50

40

30

20

10

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Step load

39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71




Width


Load ()WC40

(a) (b)


WC60noncontact (dB)

WC40noncontact (dB)

WC60contact (dB)

WC40 contact (dB)

L1 average ndash020 ndash019 ndash098 ndash210L2 average ndash105 024 ndash102 ndash220L3 average ndash205 091 ndash044 ndash379

ndash400

ndash200

000

Total damage (dB)

Figure 18 Total damage in each loading branch for reinforced concrete beams under the four-point bending test


using finite-element models to explore the interaction of ul-trasonic waves inside low quality concrete with varying neutralaxis locations On the other hand when the concrete below theneutral axis index provided significant cracks the air-coupledultrasonic test proved to be sensitive due to the opening andclosing of cracks with the reinforcing bar holding the beam inplace

e neutral axis index when the tension side of theconcrete starts to crack is computed having y 49mm whilethe neutral axis index when the concrete below is redundantand only the reinforcing bar resists the moment in tension is38mm (Figure 17(a)) e wave path intersects the com-pression zone experienced by the concrete that leads to bettersensitivity of the contact ultrasonic test (Figure 17(b))

e average total damage represented by the normalizedpeak to peak amplitude for high WC60 under the non-contact ultrasonic test and low WC40 under the contactultrasonic test gave good agreement with the changes in load(Figure 18) Concrete with WC60 and WC40 under thecontact and noncontact ultrasonic test respectively was notresponsive e actual crack formation on the tension sideafter the test was recorded (Figures 19(a) and 19(b))

4 Conclusions

is paper focused on two types of specimens and testingunder the nondestructive test e plain concrete cubestested with the contact ultrasonic test with varying WCof 40 and 60 under compression load showed that nor-malized peak to peak amplitude gave good agreement andwas sensitive with the load Higher water-cement ratio gavea larger value of normalized peak to peak amplitude iswas caused by the scattering of the ultrasonic wave inside theconcrete since it contained more air voids than lower water-cement ratioe second type of the specimen and test usingreinforced concrete beams under the four-point bending testwith varying WC of 40 and 60 proved to be complex Addedparameters were considered to investigate the sensitivity ofthe contact and noncontact ultrasonic test ese were ul-trasonic wave path and the neutral axis index It showed thatthe higher water-cement ratio produced good sensitivity inthe noncontact ultrasonic test since it formed more cracksLower water-cement ratio gave good sensitivity with load forthe contact ultrasonic test since it had its ultrasonic wavepath passing the concrete experiencing compression Inaddition the neutral axis index for a member subjected tobending is an important factor in assessing the sensitivity of

both contact and noncontact ultrasonic test In futurestudies nonlinear ultrasonic test using frequency spectrumand nonlinear finite-element model can be developed toshow how the stress distribution with a varying neutral axisindex is experienced Variation of the formation of newcracks as well as closing and propagating of preexistingcracks can also be explored

Data Availability

e data came from the dissertation of the correspondingauthore data are archived in Tokyo Institute of Technology

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e research has been made possible through the support ofJapan Society for Promotion of Science (JSPS) RONPAKU

References

[1] D Breysse ldquoNondestructive evaluation of concrete strengthan historical review and a new perspective by combining NDTmethodsrdquo Construction and Building Materials vol 33pp 139ndash163 2012

[2] P Daponte F Maceri and R S Olivito ldquoUltrasonic signal-processing techniques for the measurement of damage growthin structural materialsrdquo IEEE Transactions on instrumentationand measurement vol 44 no 6 pp 1003ndash1008 1995

[3] J Zhu and J S Popovics ldquoNon-contact NDT of concretestructures using air-coupled sensorsrdquo NSEL Report SeriesDepartment of Civil and Environmental Engineering Uni-versity of Illinois 2008

[4] P H Brodeur M S Hall and C Esworthy ldquoSound dispersionand attenuation in the thickness direction of paper materialsrdquoJournal of the Acoustical Society of America vol 94 no 4pp 2215ndash2225 1993

[5] J Stor-Pellinen and M Luukkala ldquoPaper roughness mea-surement using airborne ultrasoundrdquo Sensors and ActuatorsA Physical vol 49 no 1-2 pp 37ndash40 1995

[6] K Imielin M Castaings R Wojtyra J Haras E Le Clezioand B Hosten ldquoAircoupled ultrasonic C-scan technique inimpact response testing of carbon fibre and hybrid glasscarbon and kevlarepoxy compositesrdquo Journal of MaterialsProcessing Technology vol 157-158 pp 513ndash522 2004

[7] P Purnell T H Tan D A Hutchhins and J BerrimanldquoNoncontact ultrasonic diagnostics in concrete a preliminary

Tension crack

(a) (b)

Figure 19 (a) Sample beam specimen picture during the test (b) Pictures of tension cracks for the beam specimens


investigationrdquo Cement and Concrete Research vol 34 no 7pp 1185ndash1188 2004

[8] J Berriman P Purnell D A Hutchins and A NeildldquoHumidity and aggregate content correction factors for air-coupled ultrasonic evaluation of concreterdquo Ultrasonicsvol 43 no 4 pp 211ndash217 2005

[9] A M Siddiolo L DrsquoAcquisto A R Maeva and R G MaevldquoWooden panel paintings investigation an air-coupled ul-trasonic imaging approachrdquo IEEE Transactions on Ultra-sonics Ferroelectrics and Frequency Control vol 54 no 4pp 836ndash846 2007

[10] S J Sanabria R Furrer J Neuenschwander P Niemz andP Schultz ldquoAnalytical modeling finite-difference simulationand experimental validation of air-coupled ultrasound beamrefraction and damping through timber laminates withapplication to non-destructive testingrdquo Ultrasonics vol 63pp 65ndash85 2014

[11] S iele K Kim J Qu and L J Jacobs ldquoAir-coupled de-tection of nonlinear Rayleigh surface waves to assess materialnonlinearityrdquo Ultarsonics vol 54 no 6 pp 1470ndash1475 2014

[12] G Kim J Kim K Kurtis L J Jacobs Y L Pape andM Guimares ldquoQuantitative evaluation of carbonation ofconcrete using nonlinear ultrasoundrdquo Materials and Struc-tures vol 49 no 1-2 pp 399ndash409 2016

[13] J Zhu and J S Popovics ldquoNon-contact imaging for surface-opening cracks in concrete with air-coupled sensorsrdquoMaterials and Structures vol 38 no 283 pp 801ndash806 2004

[14] J M Ongpeng A W Oreta and S Hirose ldquoEffect of loadpattern in the generation of higher harmonic amplitude inconcrete using nonlinear ultrasonic testrdquo Journal of AdvancedConcrete Technology vol 14 no 5 pp 205ndash214 2016

[15] J M Ongpeng A W Oreta S Hirose and K NakahataldquoNonlinear ultrasonic investigation of concrete with varyingaggregate size under uniaxial compression loading andunloadingrdquo Journal of Materials in Civil Engineering vol 29no 2 article 04016210 2016

[16] J M Ongpeng ldquoUltrasonic pulse velocity test of reinforcedconcrete with induced corrosionrdquo ASEAN EngineeringJournal Part C vol 6 no 1 pp 5ndash12 2017

[17] J M Ongpeng M Soberano A W Oreta and S HiroseldquoArtificial neural network model using ultrasonic test resultsto predict compressive stress in concreterdquo Computers andConcrete vol 19 no 1 pp 59ndash68 2017

[18] J M Ongpeng A W Oreta and S Hirose ldquoInvestigation onthe sensitivity of ultrasonic test applied to reinforced concretebeams using neural networkrdquo Applied Sciences vol 8 no 3p 405 2018

[19] BS 1881203 Recommendations for Measurement of Velocity ofUltrasonic Pulses in Concrete British Standards InstitutionLondon UK 1986

[20] K F Bompan and V G Haach ldquoUltrasonic tests in theevaluation of the stress level in concrete prisms based onacoustoelasticityrdquo Construction and Building Materialsvol 162 pp 740ndash750 2018

[21] G C W Kim J Y Kim K E Kurtis and L J Jacobs ldquoAir-coupled detection of nonlinear Rayleigh surface waves inconcretendashapplication to microcracking detectionrdquo NDT amp EInternational vol 67 pp 64ndash70 2014

[22] F Moradi-Marani P Rivard C P Lamarche and S A KodjoldquoEvaluating the damage in reinforced concrete slabs underbending test with the energy of ultrasonic wavesrdquo Con-struction and Building Materials vol 73 pp 663ndash673 2014

[23] G J Kim S J Park and H G Kwak ldquoExperimental char-acterization of ultrasonic nonlinearity under cyclic change of

prestressing force using nonlinear ultrasonic spectroscopyrdquoConstruction and Building Materials vol 157 pp 700ndash7072017

[24] D H Sigurdardottir and B Glisic ldquoe neutral axis locationfor structural health monitoring an overviewrdquo Journal ofCivil and Structural Health Monitoring vol 5 no 5pp 703ndash713 2015

[25] Y Y Lim S T Smith and C K Soh ldquoWave propagationbased monitoring of concrete curing using piezoelectricmaterials review and path forwardrdquo NDT and E In-ternational vol 99 pp 50ndash63 2018

[26] L Espinosa F Prieto L Brancheriau and P LasayguesldquoEffect of wood anisotropy in ultrasonic wave propagationa ray-tracing approachrdquo Ultrasonics vol 91 pp 242ndash2512019


International Journal of

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Submit your manuscripts atwwwhindawicom

inspection of wood and quality control of paper art objectsand advanced composite materials used in the aerospaceindustry [3] Quality tests in paper focused on sound dis-persion and attenuation and estimation of its surfaceroughness can be monitored [4 5] In construction buildingmaterials this method is now being developed for noncontactdetection of surface waves in concrete [3] Additionally theimpact response test in the composite material using theC-scan technique is also being developed in diagnosingconcrete [6ndash8] Various studies including wooden panelpainting investigation and refraction including damping oftimber laminates are also done in previous researches [9 10]

Air-coupled ultrasonic test is gaining popularity andadvancement Waves in metals and composite materialshave been successfully detected through the application ofsensors having frequency of 50 kHz to 1MHz In testingconcrete a flat frequency response below 100 kHz is idealLow-frequency range sensors detect leaky waves in concreteIt is also proven that the use of air-coupled sensors is notsensitive to surface conditions in concrete and is sensitive tothe existence of cracks as waves propagate across it [3] It canalso assess material nonlinearity [11] including carbonationinside concrete materials [12] As the noncontact testmethod enables fast scanning of large structures the am-plitude information that is obtained is dependable andconsistent when it is transmitted to the solid material [13]

e received time-domain waveform is the commondata retrieved in this test e parameters that are measuredin time-domain waveform are time of arrival and peak topeak amplitude Time of arrival of an ultrasonic wavepassing through a dense medium should be smaller than theporous or damaged material Peak to peak amplitude issensitive to scattering of ultrasonic waves passing throughthe medium In addition received time-domain waveform isconverted to frequency-domain waveform using fast Fouriertransform e parameters under frequency-domainwaveform consist of fundamental amplitude and higherharmonic amplitudes Previous research show that plainconcrete cubes with different load-loading patterns greatlyinfluences the higher harmonics parameters [14] Com-plexity in the damage level for concrete is recognized whendifferent sizes of aggregates inside concrete are present [15]From references the UPV test is convenient in detectingflaws like corrosion inside concrete [16] but it is insensitiveto the internal damage In addition for plain concrete cubesthe correlation of ultrasonic parameters to internal damagerepresented by changes in load was done using artificialneural network model and it indicated that UPV has veryweak correlation compared to peak to peak amplitude of thetime-domain waveform [17] Investigation of reinforcedconcrete beams was considered using the artificial neuralnetwork model e results showed that the contact-typeultrasonic test using peak to peak amplitude as a parameterto detect damage was classified as long- and short-rangesensitivity for WC40 and WC60 respectively Long- andshort-range sensitivity from the model developed can detectdamage more than 20 and less than 20 respectively [18]

In this paper peak to peak amplitude of time-domainwaveform is used as a parameter to measure the damage

Decrease in peak to peak amplitude is evident when there isa scattering of the ultrasonic wave upon loading e ex-perimental test involved two test methods for both water-cement ratio (WC) 60 and 40ese are the compression testof sixteen cube specimens of size 150mm on each side andsix concrete beams under the four-point bending test ecompression test is established to show the sensitivity of thepeak to peak amplitude using the contact ultrasonic testwhile the four-point bending test is performed to show therelationship of the reinforced concrete beamrsquos load neutralaxis index and the peak to peak amplitude for both thecontact and noncontact ultrasonic test

2 Plain Concrete Cubes under Compression

Sixteen concrete cubes were casted having size of 150mm times

150mm times 150mm Varying water-cement ratios of WC40and WC60 were used to investigate the effect of the test withdifferent water-cement ratios e maximum size of aggre-gates used was 20mm and the ratio of sand-total aggregatewas 45 Table 1 shows the content of the ingredients Auniversal testing machine was used and each specimen wassubjected to the compression test at their mature age of 28days e compressive strength of WC40 and WC60 wastested prior to the experiment and resulted to characteristicstrength of 53MPa and 40MPa respectively e rate ofloadingunloading was 05 kN per second with the loadpattern (Figure 1) Four loading branches were consideredhaving a percent load of 0 to 20 0 to 40 0 to 60and 0 to 100 respectively

Specimens were tested by uniaxial compressive load(Figure 2(a)) Pitch-catch ultrasonic test was used to recordthe time-domain waveforms in each loading or unloadingstep A high-gain broadband receiver and two transducersconnected to the oscilloscope with tone-burst pulser wereused in the setup e supplied voltage was set at 1800 voltswith the sine wave having 10 cycles at 100 kHz In additionthe low-pass filter was set at 3MHz and the high-pass filterwas set at 50 kHz with an input impedance of 50Ω Directtransmission was implemented in the wave path of theultrasonic wave from the transmitting to the receivingtransducers (Figure 2(b)) is wave path was passingthrough the concrete experiencing compression etransmitting and receiving transducers were carefullyaligned centered and bonded to the concrete cubes with gel-couplants e transmitting transducer had its generatingfrequency at 100 kHz that sent signal across the specimene receiving transducer on the contrary had 200 kHzfrequency and was placed on the opposite face is fre-quency of transducers proved to be effective in measuringinternal damage inside the concrete material [14 15]

Time-domain waveforms were recorded for the firstloading branch of 0 20 40 60 and 80 (Figure 3) Itwas observed that the peak to peak amplitude decreases withrespect to increasing load A damage level assessment is usedin this paper by solving its normalized peak to peak am-plitude in decibels as seen in Equation (1) It followed theconcepts in electrical circuits which dissipated power fromone state to the other is parameter is used to measure




1113874 1113875

(1)















0

20

40

60

80

100

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Perc

ent l

oad

Step load


3rd

1st 2nd





Transmitter100 kHz

Receiver200 kHz

Load

Rigid base


Pulserreceiver

(a)

Wave path

Receiver15

1015

00 510

1515

Transmitter

10

5z (cm

)

0

y (cm) x (cm)

(b)


08

Am

plitu

de (v

olts)

060402


Time





ndash30

ndash20

ndash10

0

0

20

40

60

80

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Paek

to p

eak

ampl

itude

(dB)

Perc

ent l

oad

Step load

LoadWC40WC60




ndash50

Total damage (dB)


9mm diameter bar

100mm 400mm

Cover = 10mm100mm



BeamP2 P2

Oil hydraulic pump








(2)



tension

0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Perc

ent l

oad

Step load

L3

L2

L1




Support

P2 P2




Receiver

ReceiverSupport






ndash400

ndash300

ndash200

ndash100

000

0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Peak

to p

eak

ampl

itude

(dB)

Perc

ent l

oad

Step load




0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Peak

to p

eak

ampl

itude

(dB)

Perc

ent l

oad

Step load



h d

(a) (b) (c)

Neutral axis

εs

εc

y

bAs

Fst

Fcc Mo

εt







00000

00100

00200

00300

00400

00500

00600

ndash00060

ndash00050

ndash00040

ndash00030

ndash00020

ndash00010

00000

Botto

m fi

ber s

trai

n (m

m)

Top

fiber

stra

in (m

m)

Time



L1L2

L3


00000

00050

00100

00150

00200

00250

ndash00030

ndash00025

ndash00020

ndash00015

ndash00010

ndash00005

00000

Tens

ile st

rain

(mm

)

Com

pres

sive s

trai

n (m

m)

Time





100


Neu

tral

axis

at m

idsp

an (m

m)

ndash10

0

ndash20

ndash30

ndash40

ndash50

ndash60

ndash70

ndash80

ndash90

ndash100

90

Perc

ent l

oad

80

70

60

50

40

30

20

10

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Step load

(a) (b)

39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71



Width


Load ()WC60



100


eutr

al ax

is at

mid

span

(mm

)ndash10

0

ndash20

ndash30

ndash40

ndash50

ndash60

ndash70

ndash80

ndash90

ndash100

90

Perc

ent l

oad

80

70

60

50

40

30

20

10

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Step load

39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71




Width


Load ()WC40

(a) (b)


WC60noncontact (dB)

WC40noncontact (dB)

WC60contact (dB)

WC40 contact (dB)


ndash400

ndash200

000

Total damage (dB)






4 Conclusions



Data Availability




Acknowledgments


References








Tension crack

(a) (b)



























RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia




1113874 1113875

(1)















0

20

40

60

80

100

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Perc

ent l

oad

Step load


3rd

1st 2nd





Transmitter100 kHz

Receiver200 kHz

Load

Rigid base


Pulserreceiver

(a)

Wave path

Receiver15

1015

00 510

1515

Transmitter

10

5z (cm

)

0

y (cm) x (cm)

(b)


08

Am

plitu

de (v

olts)

060402


Time





ndash30

ndash20

ndash10

0

0

20

40

60

80

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Paek

to p

eak

ampl

itude

(dB)

Perc

ent l

oad

Step load

LoadWC40WC60




ndash50

Total damage (dB)


9mm diameter bar

100mm 400mm

Cover = 10mm100mm



BeamP2 P2

Oil hydraulic pump








(2)



tension

0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Perc

ent l

oad

Step load

L3

L2

L1




Support

P2 P2




Receiver

ReceiverSupport






ndash400

ndash300

ndash200

ndash100

000

0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Peak

to p

eak

ampl

itude

(dB)

Perc

ent l

oad

Step load




0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Peak

to p

eak

ampl

itude

(dB)

Perc

ent l

oad

Step load



h d

(a) (b) (c)

Neutral axis

εs

εc

y

bAs

Fst

Fcc Mo

εt







00000

00100

00200

00300

00400

00500

00600

ndash00060

ndash00050

ndash00040

ndash00030

ndash00020

ndash00010

00000

Botto

m fi

ber s

trai

n (m

m)

Top

fiber

stra

in (m

m)

Time



L1L2

L3


00000

00050

00100

00150

00200

00250

ndash00030

ndash00025

ndash00020

ndash00015

ndash00010

ndash00005

00000

Tens

ile st

rain

(mm

)

Com

pres

sive s

trai

n (m

m)

Time





100


Neu

tral

axis

at m

idsp

an (m

m)

ndash10

0

ndash20

ndash30

ndash40

ndash50

ndash60

ndash70

ndash80

ndash90

ndash100

90

Perc

ent l

oad

80

70

60

50

40

30

20

10

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Step load

(a) (b)

39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71



Width


Load ()WC60



100


eutr

al ax

is at

mid

span

(mm

)ndash10

0

ndash20

ndash30

ndash40

ndash50

ndash60

ndash70

ndash80

ndash90

ndash100

90

Perc

ent l

oad

80

70

60

50

40

30

20

10

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Step load

39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71




Width


Load ()WC40

(a) (b)


WC60noncontact (dB)

WC40noncontact (dB)

WC60contact (dB)

WC40 contact (dB)


ndash400

ndash200

000

Total damage (dB)






4 Conclusions



Data Availability




Acknowledgments


References








Tension crack

(a) (b)



























RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia




Transmitter100 kHz

Receiver200 kHz

Load

Rigid base


Pulserreceiver

(a)

Wave path

Receiver15

1015

00 510

1515

Transmitter

10

5z (cm

)

0

y (cm) x (cm)

(b)


08

Am

plitu

de (v

olts)

060402


Time





ndash30

ndash20

ndash10

0

0

20

40

60

80

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Paek

to p

eak

ampl

itude

(dB)

Perc

ent l

oad

Step load

LoadWC40WC60




ndash50

Total damage (dB)


9mm diameter bar

100mm 400mm

Cover = 10mm100mm



BeamP2 P2

Oil hydraulic pump








(2)



tension

0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Perc

ent l

oad

Step load

L3

L2

L1




Support

P2 P2




Receiver

ReceiverSupport






ndash400

ndash300

ndash200

ndash100

000

0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Peak

to p

eak

ampl

itude

(dB)

Perc

ent l

oad

Step load




0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Peak

to p

eak

ampl

itude

(dB)

Perc

ent l

oad

Step load



h d

(a) (b) (c)

Neutral axis

εs

εc

y

bAs

Fst

Fcc Mo

εt







00000

00100

00200

00300

00400

00500

00600

ndash00060

ndash00050

ndash00040

ndash00030

ndash00020

ndash00010

00000

Botto

m fi

ber s

trai

n (m

m)

Top

fiber

stra

in (m

m)

Time



L1L2

L3


00000

00050

00100

00150

00200

00250

ndash00030

ndash00025

ndash00020

ndash00015

ndash00010

ndash00005

00000

Tens

ile st

rain

(mm

)

Com

pres

sive s

trai

n (m

m)

Time





100


Neu

tral

axis

at m

idsp

an (m

m)

ndash10

0

ndash20

ndash30

ndash40

ndash50

ndash60

ndash70

ndash80

ndash90

ndash100

90

Perc

ent l

oad

80

70

60

50

40

30

20

10

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Step load

(a) (b)

39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71



Width


Load ()WC60



100


eutr

al ax

is at

mid

span

(mm

)ndash10

0

ndash20

ndash30

ndash40

ndash50

ndash60

ndash70

ndash80

ndash90

ndash100

90

Perc

ent l

oad

80

70

60

50

40

30

20

10

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Step load

39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71




Width


Load ()WC40

(a) (b)


WC60noncontact (dB)

WC40noncontact (dB)

WC60contact (dB)

WC40 contact (dB)


ndash400

ndash200

000

Total damage (dB)






4 Conclusions



Data Availability




Acknowledgments


References








Tension crack

(a) (b)



























RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia







(2)



tension

0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Perc

ent l

oad

Step load

L3

L2

L1




Support

P2 P2




Receiver

ReceiverSupport






ndash400

ndash300

ndash200

ndash100

000

0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Peak

to p

eak

ampl

itude

(dB)

Perc

ent l

oad

Step load




0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Peak

to p

eak

ampl

itude

(dB)

Perc

ent l

oad

Step load



h d

(a) (b) (c)

Neutral axis

εs

εc

y

bAs

Fst

Fcc Mo

εt







00000

00100

00200

00300

00400

00500

00600

ndash00060

ndash00050

ndash00040

ndash00030

ndash00020

ndash00010

00000

Botto

m fi

ber s

trai

n (m

m)

Top

fiber

stra

in (m

m)

Time



L1L2

L3


00000

00050

00100

00150

00200

00250

ndash00030

ndash00025

ndash00020

ndash00015

ndash00010

ndash00005

00000

Tens

ile st

rain

(mm

)

Com

pres

sive s

trai

n (m

m)

Time





100


Neu

tral

axis

at m

idsp

an (m

m)

ndash10

0

ndash20

ndash30

ndash40

ndash50

ndash60

ndash70

ndash80

ndash90

ndash100

90

Perc

ent l

oad

80

70

60

50

40

30

20

10

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Step load

(a) (b)

39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71



Width


Load ()WC60



100


eutr

al ax

is at

mid

span

(mm

)ndash10

0

ndash20

ndash30

ndash40

ndash50

ndash60

ndash70

ndash80

ndash90

ndash100

90

Perc

ent l

oad

80

70

60

50

40

30

20

10

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Step load

39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71




Width


Load ()WC40

(a) (b)


WC60noncontact (dB)

WC40noncontact (dB)

WC60contact (dB)

WC40 contact (dB)


ndash400

ndash200

000

Total damage (dB)






4 Conclusions



Data Availability




Acknowledgments


References








Tension crack

(a) (b)



























RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia





ndash400

ndash300

ndash200

ndash100

000

0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Peak

to p

eak

ampl

itude

(dB)

Perc

ent l

oad

Step load




0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64

Peak

to p

eak

ampl

itude

(dB)

Perc

ent l

oad

Step load



h d

(a) (b) (c)

Neutral axis

εs

εc

y

bAs

Fst

Fcc Mo

εt







00000

00100

00200

00300

00400

00500

00600

ndash00060

ndash00050

ndash00040

ndash00030

ndash00020

ndash00010

00000

Botto

m fi

ber s

trai

n (m

m)

Top

fiber

stra

in (m

m)

Time



L1L2

L3


00000

00050

00100

00150

00200

00250

ndash00030

ndash00025

ndash00020

ndash00015

ndash00010

ndash00005

00000

Tens

ile st

rain

(mm

)

Com

pres

sive s

trai

n (m

m)

Time





100


Neu

tral

axis

at m

idsp

an (m

m)

ndash10

0

ndash20

ndash30

ndash40

ndash50

ndash60

ndash70

ndash80

ndash90

ndash100

90

Perc

ent l

oad

80

70

60

50

40

30

20

10

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Step load

(a) (b)

39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71



Width


Load ()WC60



100


eutr

al ax

is at

mid

span

(mm

)ndash10

0

ndash20

ndash30

ndash40

ndash50

ndash60

ndash70

ndash80

ndash90

ndash100

90

Perc

ent l

oad

80

70

60

50

40

30

20

10

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Step load

39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71




Width


Load ()WC40

(a) (b)


WC60noncontact (dB)

WC40noncontact (dB)

WC60contact (dB)

WC40 contact (dB)


ndash400

ndash200

000

Total damage (dB)






4 Conclusions



Data Availability




Acknowledgments


References








Tension crack

(a) (b)



























RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia






00000

00100

00200

00300

00400

00500

00600

ndash00060

ndash00050

ndash00040

ndash00030

ndash00020

ndash00010

00000

Botto

m fi

ber s

trai

n (m

m)

Top

fiber

stra

in (m

m)

Time



L1L2

L3


00000

00050

00100

00150

00200

00250

ndash00030

ndash00025

ndash00020

ndash00015

ndash00010

ndash00005

00000

Tens

ile st

rain

(mm

)

Com

pres

sive s

trai

n (m

m)

Time





100


Neu

tral

axis

at m

idsp

an (m

m)

ndash10

0

ndash20

ndash30

ndash40

ndash50

ndash60

ndash70

ndash80

ndash90

ndash100

90

Perc

ent l

oad

80

70

60

50

40

30

20

10

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Step load

(a) (b)

39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71



Width


Load ()WC60



100


eutr

al ax

is at

mid

span

(mm

)ndash10

0

ndash20

ndash30

ndash40

ndash50

ndash60

ndash70

ndash80

ndash90

ndash100

90

Perc

ent l

oad

80

70

60

50

40

30

20

10

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Step load

39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71




Width


Load ()WC40

(a) (b)


WC60noncontact (dB)

WC40noncontact (dB)

WC60contact (dB)

WC40 contact (dB)


ndash400

ndash200

000

Total damage (dB)






4 Conclusions



Data Availability




Acknowledgments


References








Tension crack

(a) (b)



























RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia


100


Neu

tral

axis

at m

idsp

an (m

m)

ndash10

0

ndash20

ndash30

ndash40

ndash50

ndash60

ndash70

ndash80

ndash90

ndash100

90

Perc

ent l

oad

80

70

60

50

40

30

20

10

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Step load

(a) (b)

39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71



Width


Load ()WC60



100


eutr

al ax

is at

mid

span

(mm

)ndash10

0

ndash20

ndash30

ndash40

ndash50

ndash60

ndash70

ndash80

ndash90

ndash100

90

Perc

ent l

oad

80

70

60

50

40

30

20

10

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Step load

39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71




Width


Load ()WC40

(a) (b)


WC60noncontact (dB)

WC40noncontact (dB)

WC60contact (dB)

WC40 contact (dB)


ndash400

ndash200

000

Total damage (dB)






4 Conclusions



Data Availability




Acknowledgments


References








Tension crack

(a) (b)



























RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia





4 Conclusions



Data Availability




Acknowledgments


References








Tension crack

(a) (b)



























RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia


























RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia


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