Toughness of Railroad Concrete Crossties with Holes and Web Openings

Technical Note Toughness of Railroad Concrete Crossties with Holes and Web Openings

Erosha K. Gamage 1, Sakdirat Kaewunruen 1,2,*, Alex M. Remennikov 3 and Tetsuya Ishida 4

1 Department of Civil Engineering, School of Engineering, The University of Birmingham, Edgbaston B15 2TT, UK; [email protected] 2 Birmingham Centre for Railway Research and Education, School of Engineering, The University of Birmingham, Edgbaston B15 2TT, UK 3 School of Civil, Mining, and Environmental Engineering, University of Wollongong, Northﬁeld Ave, Wollongong, NSW 2522, Australia; [email protected] 4 Concrete Laboratory, Department of Civil Engineering, University of Tokyo, 7 Chome-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan; [email protected] * Correspondence: [email protected]; Tel.: +44-121-414-2670

Academic Editors: Higinio González Jorge and Pedro Arias-Sánchez Received: 30 June 2016; Accepted: 6 January 2017; Published: 11 January 2017

Abstract: Prestressed concrete sleepers (or railroad ties) are principally designed in order to carry wheel loads from the rails to the ground of railway tracks, as well as to secure rail gauge for safe train travels. Their design takes into account static and dynamic loading conditions. In spite of prestressed concrete crossties being most commonly used in railway tracks, there have always been many demands from rail engineers to improve the serviceability and functionality of concrete crossties. For example, signaling, fiber optic, equipment cables are often damaged either by ballast corners or by the tamping machine. There has been a need to re-design concrete crossties to incorporate cables internally so that they would not experience detrimental or harsh environments. Also, many concrete crossties need a retrofit for an automatic train control device and similar signaling equipment. In contrast, the effects of holes and web openings on the structural capacity of concrete crossties have not been thoroughly investigated. This paper accordingly highlights the experimental investigations into the effect of holes and web openings on the toughness and ductility of concrete crossties. The key outcome of this research is to enable a better decision making process for retrofitting prestressed concrete crossties with holes and web openings in practice.

Keywords: concrete sleeper; crosstie; design standard; holes; web opening; railway infrastructure; static performance

1. Introduction Railroad is a standout method amongst the most essential and broadly utilized means of transportation, conveying cargo, passengers, minerals, grains, and so forth. Railway prestressed concrete crossties have been utilized in the railway industry for over 50 years [1–3]. The railroad ties (called ‘railway sleepers’) are a main part of railway track structures. The crossties can be made of timber, concrete, steel or other engineered materials [4]. Concrete crossties were initially introduced many decades ago and at present have been introduced almost everywhere in the world. Their major role is to distribute loads from the rail foot to the underlying ballast bed. Railroad track structures often experience impact loading conditions due to wheel/rail interactions associated with abnormalities in either a wheel or a rail [1]. In addition, railroad track components are often being modiﬁed at construction sites to ﬁt with signaling gears, cables, and additional train derailment protections, such as guard rails, check rails, earthquake protection rails, etc. The practical guidelines for crosstie

Infrastructures 2017, 2, 3; doi:10.3390/infrastructures2010003 www.mdpi.com/journal/infrastructures Infrastructures 2017, 2, 3 2 of 8 retroﬁt have not been well established and many attempts were carried out based on trial and error. Despite being a common task in construction sites, the behavior of holes and web openings on concrete crossties has not been well documented in open literature. A review of existing standard design codes (e.g., EN13230-2,Infrastructures AREMA2017, 2, 3 C4, AS1095.14, or ACI) reveals that there is a necessity to investigate2 of 8 such important aspects [2]. In this manner, it is important to ensure that concrete crossties can be safely for crosstie retrofit have not been well established and many attempts were carried out based on trial retrofittedand anderror. modified Despite being for add-on a common fixtures task inin practice.construction Also, sites, note the thatbehavior a key of performance holes and web criterion in existingopenings design on principlesconcrete crossties (i.e., limithas not states been well design documented concept in and open permissible literature. A stressreview designof existing principle) still reliesstandard on ultimate design staticcodes performance.(e.g., EN13230-2, The AREMA ultimate C4, capacityAS1095.14, of or concrete ACI) reveals crossties that there indicates is a many structuralnecessity features to investigate with respect such to important the dynamic aspects and [2]. serviceIn this manner, performance it is important of crossties. to ensure The that emphasis of this studyconcrete has crossties been placed can be onsafely the retrofitted experimental and modi studiesfied for into add-on energy fixtures toughness in practice. of the Also, crossties note with that a key performance criterion in existing design principles (i.e., limit states design concept and holes andpermissible web openings. stress design This principle) characteristic, still relies which on ultimate is not static well performance. known, is anThe important ultimate capacity factor in the structuralof concrete design ofcrossties concrete indicates crossties, many especially structural forfeatures the failurewith respect mode to identification the dynamic and at ultimateservice state. The toughnessperformance characteristic of crossties. has The a correlationemphasis of withthis st theudy residual has been performance placed on the ofexperimental sleepers under studies dynamic and impactinto loadingenergy toughness conditions of the [3]. crossties The insight with holes into and these web behaviors openings. will This not characteristic, only improve which the is not safety and reliabilitywell of known, railway is infrastructure,an important factor but in will the enhancestructural the design structural of concrete safety crossties, of other especially concrete for structures.the failure mode identification at ultimate state. The toughness characteristic has a correlation with the 2. Experimentalresidual performance Evaluation of sleepers under dynamic and impact loading conditions [3]. The insight into these behaviors will not only improve the safety and reliability of railway infrastructure, but will Theenhance holes the and structural web openings safety of other are generatedconcrete structures. using a high-speed coring machine on full-scale crossties. Common types of holes and web openings in practice have been carried out, including the 2. Experimental Evaluation vertical and longitudinal holes as well as the lateral through hole, as illustrated in Figure1, in order to accompanyThe other holes systems’ and web needs openings as demonstrated are generated using in Figure a high-speed2. For practicality, coring machine 42 mmon full-scale diameter holes have beencrossties. cored inCommon a similar types manner of holes as and in an web actual openings construction. in practice Then, have theybeen carried are tested out, under including the the prescribed vertical and longitudinal holes as well as the lateral through hole, as illustrated in Figure 1, in order static testingto accompany condition other in ordersystems’ to identifyneeds as thedemonstrated comparable in Figure and repeatable 2. For practicality, residual 42 energy mm diameter toughness [5]. The benchmarkingholes have been test cored method, in a similar in accordance manner as with in an European actual construction. Standard Then, EN 13230-2,they are tested has been under adopted for thisthe study prescribed [2]. The static static testing setup condition includes in threeorder pointto identify bending the comparable tests with and the repeatable span length residual of 600 mm. Throughenergy the static toughness tests, [5]. the The load benchmarking carrying capacity test meth isod, plotted in accordance against with railseat European deflection. Standard The EN fracture toughness13230-2, can subsequently has been adopted be identifiedfor this study by [2]. the The integration static setup (area includes under three the point curve) bending of the tests load–deflection with the span length of 600 mm. Through the static tests, the load carrying capacity is plotted against relationship [6]. The comparative index is a ratio between the toughness with and without holes. railseat deflection. The fracture toughness can subsequently be identified by the integration (area In general,In thegeneral, full the load–deflection full load–deflection curve curve can can be be found found in in FigureFigure 33.. The The first first stage stage of the of thecurve curve is is underthe elasticthe curve) stage of whenthe load–deflection materials behave relationship linearly [6].in anThe elastic comparative range. Then,index isthe a rationonlinear between behavior the the elastictoughnesstakes stage place when with when and materials withoutthe principalbehave holes. stress linearly reaches in the an proportional elastic range. yield Then, stress the and nonlinear the materials behavior make takes place whenuse the of the principal nonlinear stress portion reaches of the thestrength. proportional Until the structural yield stress member and reaches the materials ultimate make capacity use or of the nonlinearstability portion failure, of the the strength. nonlinear Until portion the dominates. structural At member the ultimate reaches point, ultimate the load–deflection capacity orcurve stability failure, thedrops nonlinear to a certain portion extent dominates. due to the crushing At the and ultimate the spalling point, of concrete. the load–deflection Then, yielding curveand a later drops to a certain extentsnap of duehigh tostrength the crushing strands cause and thea strength spalling drop of in concrete. the moment–deflection Then, yielding curve. and The a laterstrength snap of beyond this ultimate capacity, if the member is further loaded, is referred to as the residual fracture high strength strands cause a strength drop in the moment–deflection curve. The strength beyond this toughness in the post failure mechanism. The post failure mechanism can be clearly seen in Figure 3. ultimate capacity,It exhibits if that the the member strands is still further provide loaded, the streng is referredth hardening to as theeffects residual to the residual fracture load toughness carryingin the post failurecapacity mechanism. and the Theenergy post absorption failure mechanism unt canil they be clearlyreach the seen rupture in Figure capacity.3 . ItThe exhibits hardening that the strands stilleffect provide is significant the strength when more hardening tendons effects remain to and the the residual effect decreases load carrying as the remaining capacity andnumber the of energy absorptiontendons mechanism diminishes until [7–8]. they reach the rupture capacity. The hardening effect is signiﬁcant when more tendons remain and the effect decreases as the remaining number of tendons diminishes [7,8].

(a) (b)

Figure 1. Cont. Infrastructures 2017, 2, 3 3 of 8 InfrastructuresInfrastructures 2017 ,2017 2, 3, 2, 3 3 of 8 3 of 8 Infrastructures 2017, 2, 3 3 of 8

(c) (d) Figure 1. Web opening and (holesc) in crossties in practice: (a) Full(d )cross section of a traditional Figure 1. Web opening and holes(c) in crossties in practice: (a)( Fulld) cross section of a traditional Figurestandard-gauge 1. Web opening railway and concrete holes crosstie; in crossties (b) Web in Opening practice: (or (transversea) Full cross hole); section (c) Vertical of hole;a traditional (d) standard-gaugeFigureLongitudinal 1. Web railway opening or through concrete and hole. holes These crosstie; in holescrossties (b are) Web ofinten Openingpractice: installed (after (ora) Full transverseconstruction cross section hole); to accommodate of (c )aVertical traditional hole; standard-gauge railway concrete crosstie; (b) Web Opening (or transverse hole); (c) Vertical hole; (d) (d)standard-gauge Longitudinalvarious needs, or railway throughsuch as concretecables, hole. additional Thesecrosstie; holes bolts, (b) Web area br oftenacing Opening system, installed (or lateral transverse after or constructionthird hole); rail fixtures, (c) Vertical to etc. accommodate The hole; (d) Longitudinal or through hole. These holes are often installed after construction to accommodate variousLongitudinalposition needs, of suchor the through hole as cables, is oftenhole. additionalat These the middle holes bolts, betw are een aof bracingten the installededge system, of the after rail lateral constructionand the or sleeper third to railend accommodate (with ﬁxtures, etc. variousreduction needs, to such about as halfcables, of the additional maximum bolts, of the a shea bracingr force system, action). lateral No steel or reinforcement third rail fixtures, has been etc. The Thevarious position needs, of the such hole as iscables, often additional at the middle bolts, between a bracing the system, edge oflateral the railor third and rail the fixtures, sleeper endetc. The (with positiondamaged of the from hole these is often holes atand the web middle openings. betw Theeen st andard-gaugethe edge of thecrossties rail and(0.285 the × 0.175sleeper × 2.5 end m3) (with reductionposition to of about the hole half is of often the maximumat the middle of thebetw sheareen the force edge action). of the No rail steel and reinforcementthe sleeper end has (with been reductionused asto aboutspecimens half wereof the manufactured maximum of in the the shea samer forcebed underaction). ISO9001 No steel Quality reinforcement Standard with has been 3 damagedreduction from to theseabout holeshalf of and the webmaximum openings. of the The shea standard-gauger force action). No crossties steel reinforcement (0.285 × 0.175 has× 2.5been m ) damagedmaterial from deviation these holesless than and 2%. web Two openings. specimens The were st usedandard-gauge for each case crossties of hole and (0.285 web ×opening. 0.175 × Its 2.5 m3) useddamaged as specimens from these were holes manufactured and web openings. in the The same standard-gauge bed under ISO9001crossties (0.285 Quality × 0.175 Standard × 2.5 m with3) used characteristicas specimens positive were bending manufactured moment atin railsea the tsame (25t axle bed load) under as per ISO9001 EN13230-6 Quality is about Standard 34 kN·m with materialused as deviation specimens less were than manufactured 2%. Two specimens in the weresame usedbed under for each ISO9001 case of Quality hole and Standard web opening. with material(excluding deviation accidental less than loading). 2%. Two specimens were used for each case of hole and web opening. Its Its characteristicmaterial deviation positive less bendingthan 2%. momentTwo specimens at railseat were (25t used axle for load) each as case per of EN13230-6 hole and web is about opening. 34 kN Its·m characteristic positive bending moment at railseat (25t axle load) as per EN13230-6 is about 34 kN·m (excludingcharacteristic accidental positive loading). bending moment at railseat (25t axle load) as per EN13230-6 is about 34 kN·m (excluding accidental loading). (excluding accidental loading).

(a) (b)

Figure 2. Needs for modification to suit cables and pipes (a); and advanced signaling systems (b).

(a) (b) (a) (b) Figure 2. Needs for modification to suit cables and pipes (a); and advanced signaling systems (b). FigureFigure 2. Needs2. Needs for for modiﬁcation modification to to suit suit cables cables andand pipespipes (a); and advanced advanced signaling signaling systems systems (b ().b ).

Figure 3. A schematic full load–deflection curve of a structural member, representing energy toughness of the member. The toughness is a fundamental characteristic of the structural or mechanical component in compliance with the ‘conservation of energy’ principle.

Figure 3. A schematic full load–deflection curve of a structural member, representing energy Figure 3. A schematic full load–deflection curve of a structural member, representing energy Figuretoughness 3. A schematic of the member. full load–deﬂection The toughness curve isof a afundam structuralental member, characteristic representing of the energy structural toughness or toughness of the member. The toughness is a fundamental characteristic of the structural or of themechanical member. component The toughness in compliance is a fundamental with the characteristic ‘conservation of of the energy’ structural principle. or mechanical component mechanical component in compliance with the ‘conservation of energy’ principle. in compliance with the ‘conservation of energy’ principle. Infrastructures 2017, 2, 3 4 of 8

3. Results The holes and web openings are established on full-scale concrete crossties using a high-speed diamond-coring machine in order to minimize micro cracking in concrete. Common types of holes and web openings in practice are about 40 mm in diameter, which is sufﬁcient for ﬁtting industrial cables and rods.Infrastructures Critical 2017 locations, 2, 3 (such as along the shear stress path, at position right4 underof 8 the

maximumInfrastructuresInfrastructures bending3. Results 20172017 moment,,, 22,, 33 and a location for industry purposes) have been chosen44 ofof based 88 on earlier InfrastructuresInfrastructuresInfrastructures 2017, 2, 3 2017 2017, ,2 2, ,3 3 4 of 8 44 of of 8 8 numerical studies usingThe holes a ﬁnite and web element openings package are established ABAQUS on full-scale [9–12 concrete]. The crossties static tests using have a high-speed been carried 3.3. Results Results out in accordance3. Results3.diamond-coring3. Resultswith Results BS EN13230 machine forin order benchmarking to minimize mi purposescro cracking [in5 ].concrete. In this Common technical types note, of holes we focus The andholes web and openings web openings in practice are established are about 40on mm full-scale in diameter, concrete which crossties is sufficient using a forhigh-speed fitting industrial on experimentalThe holes investigationsTheThe and holesholes web and andopenings webweb into openingsopenings are structural established areare establishedestablished on toughness, full-scale onon full-scale full-scaleconcrete which concretecrosstiesconcrete is an crosstiescrosstiesusing important a high-speed usingusing aa characteristic high-speedhigh-speed to diamond-coringcables and machine rods. inCritical order locationsto minimize (such mi ascrocro along crackingcracking the shearinin concrete.concrete. stress path,CommonCommon at position typestypes ofof right holesholes under the diamond-coringdiamond-coringdiamond-coring machine machinemachinein order intoin orderminimizeorder toto minimizeminimize micro cracking mimicrocro crackingcrackingin concrete. inin concrete. concrete.Common CommonCommon types of typesholestypes ofof holesholes predict failureandand webweb for maximum openingsopenings ultimate ininbending practicepractice and moment, damageability areare aboutabout and 4040 mmmma location inin limit diameter,diameter, for states. indu whichwhichstry The is ispurposes) sufficientsufficient toughness forhavefor fittingfitting been has industrialindustrial chosen a strong based correlation on and weband andopenings webweb openingsopenings in practice inin arepracticepractice about areare 40 about aboutmm in 4040 diameter, mmmm inin diameter,diameter, which is whichwhichsufficient isis sufficientsufficient for fitting forfor industrial fittingfitting industrialindustrial to the residualcablescables andand dynamicearlier rods.rods. numerical CriticalCritical performance locationslocations studies using (such(such of a theasas finite alongalong sleepers element thethe shearshear pa [11ckage stressstress]. Under ABAQUS path,path, atat the positionposition[9–12]. ultimate The rightright static underunder limit tests thethe state,have been it is clear cables andcablescables rods. andand Critical rods.rods. locations CriticalCritical locations locations(such as (such(suchalong asasthe alongalong shear thethe stress shearshear path, stressstress at path,positionpath, atat positionrightposition under rightright the underunder thethe maximumcarried bending out inmoment, accordance and witha location BS EN13230 for indu for strystrybenchm purposes)purposes)arking purposeshavehave beenbeen [5]. chosenchosen In this basedbasedtechnical onon note, we that the damagemaximummaximummaximum under bending static bendingbendingmoment, loading moment, moment,and a mustlocation andand a bea locationforlocation considered. indu forstryfor indu indupurposes)stry However,stry purposes)purposes) have been it havehave is chosen important beenbeen based chosenchosen on to basedbased note onon that low earlierearlier numericalnumericalfocus on studiesexperimentalstudies usingusing ainvestigationsa finitefinite elementelement into papa ckageckagestructural ABAQUSABAQUS toughness, [9–12].[9–12]. which TheThe static staticis an teststestsimportant havehave beenbeencharacteristic earlier numericalearlierearlier numericalnumerical studies using studiesstudies a finite usingusing element aa finitefinite elementpaelementckage paABAQUSpackageckage ABAQUSABAQUS [9–12]. The [9–12].[9–12]. static TheThe tests staticstatic have teststests been havehave beenbeen cycle fatiguecarriedcarried failure outoutto inpredictin accordanceaccordance often failure occurs with withfor ultimate BSBS in EN13230EN13230 a similar and damageabilityforfor benchmbenchm manner.arkingarking limit Importantly, purposespurposes states. The [5].[5]. toughness InIn thethisthis technicaltechnical existing has a strong note,note, EN13230-2 wewe correlation cannot carried outcarriedcarried in accordance outout inin accordanceaccordance with BS EN13230 withwith BSBS EN13230 EN13230for benchm forforarking benchmbenchm purposesarkingarking purposespurposes [5]. In this [5].[5]. technical InIn thisthis technical technicalnote, we note,note, wewe adequatelyfocusfocus inform onon toexperimentalexperimental the engineers residual investigationsinvestigations dynamic of what performance type intointo structuralstructural of failureof the toughness,toughness, sleepers mode [11]. which theywhich Under couldisis anan the importantimportant predictultimate characteristiccharacteristic limit from state, the it initialis clear design focus on focusfocusexperimental onon experimentalexperimental investigations investigationsinvestigations into structural intointo structuralstructural toughness, toughness,toughness, which is whichwhichan important isis anan importantimportant characteristic characteristiccharacteristic toto predictpredictthat failurefailure the damageforfor ultimateultimate under andand static damageabilitydamageability loading must lilimit be states. considered. The toughness However, has it isa strongimportant correlation to note that low and cannotto informpredicttoto failure predict maintenancepredict for failurefailure ultimate forforengineers ultimateandultimate damageability andand of damageabilitydamageability what limit will states. li happenlimitmit The states.states. toughness if TheThe the toughnesstoughness operationalhas a strong hashas acorrelationa strongstrong condition correlationcorrelation is changed. toto thethe residualresidualcycle fatigue dynamicdynamic failure performanceperformance often occurs ofof thethe in sleeperssleepersa similar [11].[11]. ma nner.UnderUnder Importantly, thethe ultimateultimate the limitlimit existing state,state, EN13230-2itit isis clearclear cannot to the residualtoto thethe residualdynamicresidual dynamic dynamicperformance performanceperformance of the sleepers ofof thethe sleepers[11].sleepers Under [11].[11]. the UnderUnder ultimate thethe ultimateultimatelimit state, limitlimit it is state,state, clear itit isis clearclear This importancethatthat thethe damagedamageadequately motivates underunder inform this staticstatic engineers experimental loadingloading mustmustof what bebe study.considered.typeconsidered. of failur However,However,e mode they itit isis could importantimportant predict toto fromnotenote thatthatthe initial lowlow design that the damagethatthat thethe damageunderdamage static underunder loading staticstatic must loadingloading be mustconsidered.must bebe considered.considered. However, However,However, it is important itit isis importantimportant to note that toto note notelow thatthat lowlow The experimentalcyclecycle fatiguefatigueand failurefailurecannot results oftenofteninform revealoccursoccurs maintenance inin a aa very similarsimilar engineers interesting mamanner. of Importantly, what behavior will happenthe of existing the if the crossties EN13230-2 operationalwith cannot condition holes andis web cycle fatiguecyclecycle failure fatiguefatigue often failurefailure occurs oftenoften in occursoccurs a similar inin a a ma similarsimilarnner. mamaImportantly,nner.nner. Importantly,Importantly, the existing thethe existingEN13230-2existing EN13230-2EN13230-2 cannot cannotcannot adequatelyadequatelychanged. informinform This engineersengineers importance ofof whatwhat motivates typetype ofof failurfailurthis experimentalee modemode theythey study.couldcould predict predict fromfrom thethe initialinitial designdesign openings.adequately Table1 adequatelyadequatelyshows inform the engineers informinform ultimate engineersengineers of what moment type ofof whatwhat of failur capacities typetype e ofof mode failurfailur they ofee modemode the could crossties.theythey predict couldcould from predictpredict The the failure fromfrominitial thethe design mode initialinitial design analysisdesign has andand cannotcannot informinformThe experimental maintenancemaintenance results engineersengineers reveal ofofa verywhatwhat interesting willwill happenhappen behavior ifif thethe of operationaloperational the crossties conditioncondition with holes isis and web been evaluatedand cannot fromandand inform cannotcannot crack maintenanceinforminform propagation. maintenancemaintenance engineers It isengineersengineers of found what ofof thatwill whatwhat happen the willwill sleepers happenifhappen the operational withifif thethe fulloperationaloperational condition cross-section conditioncondition is andisis with changed.changed.openings. ThisThis importanceimportance Table 1 motivates motivatesshows the thisthis ultimate experimentalexperimental moment study.study. capaciti es of the crossties. The failure mode analysis changed.changed.changed. This importance ThisThis importanceimportance motivates motivatesmotivates this experimental thisthis experimentalexperimental study. study.study. a vertical holeThe exhibit hasexperimental been a bendingevaluated results from mode reveal crack ofa very failure.propagation. interesting We It foundbehavioris found that ofthat the therethe crossties sleepers were with with some holes full and snapscross-section web of prestressing and The experimentalTheThe experimentalexperimental results reveal resultsresults a veryrevealreveal interesting aa veryvery interestinginteresting behavior behavior behaviorof the crossties ofof thethe crosstiescrosstieswith holes withwith and holesholes web andand webweb openings.openings.with TableTable a vertical11 showsshows hole thethe ultimateultimateexhibit a momentmoment bending capaciticapaciti mode esesof ofoffailure. thethe crossties.crossties. We found TheThe that failurefailure there modemode were analysisanalysis some snaps of tendons (tendonsopenings.openings.openings. reachTable 1 their shows TableTable characteristic 1the1 showsshows ultimate thethe ultimateultimatemoment rupture momentmomentcapacitiMaximum stress)es capaciticapaciti of Moment the and esescrossties. ofof the thethe ﬁrst crossties.crossties. TheFailure bending failure TheThe M odemode failurefailure cracks analysis modemode can analysisanalysis be observed. has been prestressingevaluated from tendons crack (tendons propagation. reach It their is fo characteristicund that the sleepers rupture withstress) full and cross-section the first bending and cracks We can alsohas observe beenhas hasevaluated beenbeen that evaluatedevaluated thefrom sleepers crack fromfrom propagation. crackcrack with propagation.propagation. longitudinal It is foCapacity,und ItIt isthatis fo andfo kN·mund undthetransverse sleepersthatthat thethe sleeperswithsleepers holesfull with withcross-section failed fullfull cross-sectioncross-section by and the mixed andand shear with a verticalcan be holeobserved. exhibit We a canbending also observe mode ofthat failure. the sleeper We founds with thatlongitudinal there were and some transverse snaps holesof failed with a verticalwithwith aa holeverticalvertical exhibit holehole a exhibit exhibitbending aa bendingbendingmode of mode modefailure. ofof We failure.failure. found WeWe that foundfound there thatthat were therethere some werewere snaps somesome of snaps snaps ofof by the mixed shear and bendingMaximum mode. Moment FailureFailure MModeode and bendingprestressing mode. tendons (tendons reach theirMaximum characteristicMaximum MomentMaximum rupture Moment Moment stre ss)Failuress) andand M thetheodeFailureFailure firstfirst M M bendingbendingodeode crackscracks prestressingprestressingprestressing tendons tendons(tendonstendons (tendons (tendonsreach their reacreac Capacity,characteristichh theirtheir kN·m characteristiccharacteristic rupture strerupturerupturess) and strestre thess)ss) first andand bendingthethe firstfirst bendingcracksbending crackscracks cancan bebe observed.observed. WeWe cancan alsoalso observeobserve thatthat theCapacity,the sleepersleeper kN·mCapacity,Capacity,ss withwith kN·m kN·mlongitudinallongitudinal andand transversetransverse holesholes failedfailed can be observed.cancan bebe observed.observed. We can also WeWe canobservecan alsoalso that observeobserve the sleeper thatthat thethes sleeperwithsleeper longitudinalss withwith longitudinallongitudinal and transverse andand transversetransverse holes failed holesholes failedfailed by the mixed shear Tableand bending 1. Ultimate mode. moment capacities of concrete crossties with holes and web openings. byTable the mixed 1.byby Ultimate thethe shear mixedmixed and momentshearshear bending andand bending capacitiesmode.bending mode.mode. of concrete crossties with holes and web openings. Crossties Table 1. UltimateUltimate momentmoment capacitiescapacities ofof concreteconcrete crosstiescrossties withwith holesholes andand webweb openings.openings. Table 1. UltimateTableTable 1.1. moment UltimateUltimate capacities momentmoment capacities capacitiesof Maximumconcrete ofof crossties concreteconcrete Moment with crosstiescrossties holes withwith and holes holesweb openings. andand webweb openings. openings. CrosstiesIntact (no holes or web opening) Failure Mode Capacity, kN·m Crossties Crossties CrosstiesCrossties IntactIntact (no(no holesholes oror webweb opening)opening) 68 IntactIntact (no (no holes holesIntactIntact oror (no (no webweb holes holes opening) opening) or or web web opening) opening) (100%) Bending68 failure 6868 68 (100%)6868 (100%)(100%) (100%)Bending (100%)(100%) failure BendingBending failurefailure With 42 mm diameter vertical Bending failureBendingBending failure failure hole

With 42 mm diameter vertical With 42 mmWithWith diameter 42 42 mm mm vertical diameter diameter vertical vertical holehole 61 With 42 mm diameterhole verticalholehole hole (90%) Bending failure 6161 61 61 6161 (90%)(90%) (90%) (90%) (90%)(90%) BendingBendingBending failurefailure failure With 42 mm diameter transverse Bending failureBendingBending failure failure hole

With 42 mm diameter transverse With 42 mmWithWith diameter 42 42 mm mm transverse diameter diameter transverse transverse holehole 56 hole holehole With 42 mm diameter transverse hole (82%) Mixed bending-shear failure 5656 56 56 5656 (82%)(82%) (82%) (82%)(82%)(82%) Mixed bending-shear failure MixedMixed bending-shearMixedMixed bending-shear bending-shear bending-shear failure failure failure failure

Infrastructures 2017, 2, 3 5 of 8 With 42 mm diameter longitudinal hole Infrastructures 2017, 2, 3 5 of 8 With 42 mm Withdiameter 42 mm diameter longitudinal hole longitudinal hole

61 61 (90%) (90%) 61 MixedMixed bending-shear bending-shear failure failure (90%) Mixed bending-shear failure

Using load–deflection methodology as illustrated in Figure 4, the toughness of the crossties has been evaluatedUsin asg load–deflectionshown in Figure methodology 5. The toughne as illustratedss is the area in Figure under 4, the the load–deflection toughness of the curve, crossties has representingbeen evaluatedthe energy as absorptionshown in Figure of the 5. structuralThe toughne member.ss is the The area ductility under theindex load–deflection (based on curve, displacementrepresenting ratio) hasthe been energy derived absorption from the of ratiothe structuralof the maximum member. displace The mentductility over index the first (based on Δ Δ Δ yield displacementdisplacement of ratio) crossties has been ( max de/ rivedy). The from first the yield ratio displacement, of the maximum y, correspondsdisplacement toover the the first intersectionyield of displacement the tangents toof the crossties load displaceme (Δmax/Δy).nt The curve first at theyield origin displacement, and ultimate Δy ,displacement; corresponds to the and the intersectionmaximum displacement of the tangents represents to the load the displacemedisplacementnt curveat collapse at the state origin (as andshown ultimate in Figure displacement; 3). Therefore,and the the use maximum of the displacement representsductility ra thetio displacepresentsment a new at collapsecriterion state in addition (as shown to in the Figure 3). strengthTherefore, criterion forthe predicting use of the the displacement early warning ductility capability ratio of presents railroad acrossties. new criterion It is evident in addition that to the holes andstrength web openings criterion generally for predicting undermine the early the warningmaximum capa strengthbility of railroadconcrete crossties.crossties. ItIt iscan evident be that observedholes that and the webfirst openingscracks developed generally in undermine the crosstie the without maximum holes strength and those of concrete with vertical crossties. and It can be longitudinalobserved holes that are thebending first crackscracks. developed It is importan in thet to cr noteosstie that without the crossties holes and failed those in awith bending vertical and related mode.longitudinal In contrast, holes itare is foundbending that cracks. the cro Itsstie is importan with transverset to note hole thats failedthe crossties in the shearfailed mode, in a bending and diagonalrelated cracks mode. developed In contrast, through it is found the hole. that the crosstie with transverse holes failed in the shear mode, and diagonal cracks developed through the hole.

Figure 4. Experimental moment–deflection curves of railroad concrete crossties (0.285 × 0.175 × 2.5 m3). Average Figuredata was 4. Experimental consistently moment–deflectionobtained from two curves specimen of railroad tests. Theconcrete deviation crossties of (0.285experimental × 0.175 × 2.5 m3). results isAverage less than data 5%. Thesewas consistently figures are adoptedobtained from from [7]. two specimen tests. The deviation of experimental results is less than 5%. These figures are adopted from [7]. Infrastructures 2017, 2, 3 5 of 8

With 42 mm diameter longitudinal hole

61 Infrastructures 2017, 2, 3 (90%) 5 of 8 Mixed bending-shear failure

Using load–deflection methodology as illustrated in Figure4, the toughness of the crossties has been evaluated as shown in Figure5. The toughness is the area under the load–deflection Using load–deflection methodology as illustrated in Figure 4, the toughness of the crossties has curve, representing the energy absorption of the structural member. The ductility index (based on been evaluated as shown in Figure 5. The toughness is the area under the load–deflection curve, displacementrepresenting ratio) the has energy beenderived absorption from of thethe ratiostructural of the member. maximum The displacement ductility index over (based the firston yield displacementdisplacement of crossties ratio) has (∆max been/∆ dey).rived The from first the yield ratio displacement, of the maximum∆y, correspondsdisplacement over to the the intersection first of the tangentsyield displacement to the load of crossties displacement (Δmax/Δy curve). The atfirst the yield origin displacement, and ultimate Δy, corresponds displacement; to the and the maximumintersection displacement of the tangents represents to the the load displacement displacement at curve collapse at the state origin (as and shown ultimate in Figure displacement;3). Therefore, the useand of the the displacementmaximum displacement ductility represents ratio presents the displace a newment criterion at collapse in addition state (as shown to the in strength Figure 3). criterion Therefore, the use of the displacement ductility ratio presents a new criterion in addition to the for predicting the early warning capability of railroad crossties. It is evident that holes and web strength criterion for predicting the early warning capability of railroad crossties. It is evident that openingsholes generally and web undermineopenings generally the maximum undermine strengththe maximum of concrete strength crossties.of concrete Itcrossties. can be It observed can be that the firstobserved cracks developedthat the first in cracks the crosstie developed without in the holescrosstie and without those holes with and vertical those andwith longitudinalvertical and holes are bendinglongitudinal cracks. holes It isare important bending cracks. to note It isthat importan the crosstiest to note that failed the crossties in a bending failed in related a bending mode. In contrast,related it is mode. found In that contrast, the crosstieit is found with that the transverse crosstie with holes transverse failed inhole thes failed shear in mode,the shear and mode, diagonal cracks developedand diagonal through cracks developed the hole. through the hole.

3 Figure 4.FigureExperimental 4. Experimental moment–deflection moment–deflection curves curves of ofrailroad railroad concrete concrete crossties crossties (0.285 (0.285 × 0.175× 0.175 × 2.5 m×3).2.5 m ). AverageAverage data was data consistently was consistently obtained obtained from from two two specimen specimen tests. tests. The The deviation deviation of of experimental experimental results

isInfrastructures less thanresults 5%. 2017 is less These, 2, 3than ﬁgures 5%. These are figures adopted are fromadopted [7]. from [7]. 6 of 8

FigureFigure 5. Toughness 5. Toughness of of railroad railroad concreteconcrete crossties crossties with with holes holes and andweb webopenings. openings.

Figure 5 exhibits that the crosstie with transverse holes can absorb the least energy toughness. This also corresponds well with the ductility index results, showing that the crosstie with transverse holes failed suddenly at a brittle shear mode. In addition, it is important to note that the concrete crossties with vertical and transverse holes tend to have relatively lower ductility, resulting in less early warning of structural failure.

4. Discussion In practice, quasi-static design and analysis is adopted in a similar way as testing to simplify the process. At present, the static performance of concrete crossties or sleepers with holes and web openings cannot be realistically estimated [12–15]. This research work is a fundamental step to achieve better insight into the behavior and durability of concrete crossties with holes and web openings. Our experimental results, based on industry practice, reveal that the transverse and longitudinal holes shift the mode of failure from bending to shear-bending. This implies that the application of transverse and longitudinal holes in concrete crossties could affect longer term performance in dynamic conditions, when large deformation of crossties cannot be observed prior to the brittle shear-bending failure mode. Such action will yield very little early warning before structural failure. As a result, it is very important for track engineers to restrict or minimize the use of these holes. Based on our experimental results, we also found that the strength of materials is very consistent with standard variation of less than 3%. This significance underpins our confidence in the experimental results with a limited number of samples. However, it is very important to note that we have studied only the cases of industrial practice. Smaller sized holes and web openings (<25 mm diameter) may yield better results. We will investigate this issue further using numerical simulations in the future, in order to evaluate the size effect and the crosstie behavior under impact loadings. Using the finite element method, a three-dimensional model for crossties with different cases of holes and web openings has been calibrated by experimental results from this study [16–22]. The numerical study will enable virtual tests of the crossties with holes and web openings under different limit states (i.e., dynamic and impact conditions due to accidental loading). Our previous work [18] has indicated a relationship between the static and dynamic performance of concrete crossties; it will be further improved to estimate the dynamic capacity of concrete crossties with holes and web openings. Infrastructures 2017, 2, 3 6 of 8

Figure5 exhibits that the crosstie with transverse holes can absorb the least energy toughness. This also corresponds well with the ductility index results, showing that the crosstie with transverse holes failed suddenly at a brittle shear mode. In addition, it is important to note that the concrete crossties with vertical and transverse holes tend to have relatively lower ductility, resulting in less early warning of structural failure.

4. Discussion In practice, quasi-static design and analysis is adopted in a similar way as testing to simplify the process. At present, the static performance of concrete crossties or sleepers with holes and web openings cannot be realistically estimated [12–15]. This research work is a fundamental step to achieve better insight into the behavior and durability of concrete crossties with holes and web openings. Our experimental results, based on industry practice, reveal that the transverse and longitudinal holes shift the mode of failure from bending to shear-bending. This implies that the application of transverse and longitudinal holes in concrete crossties could affect longer term performance in dynamic conditions, when large deformation of crossties cannot be observed prior to the brittle shear-bending failure mode. Such action will yield very little early warning before structural failure. As a result, it is very important for track engineers to restrict or minimize the use of these holes. Based on our experimental results, we also found that the strength of materials is very consistent with standard variation of less than 3%. This significance underpins our confidence in the experimental results with a limited number of samples. However, it is very important to note that we have studied only the cases of industrial practice. Smaller sized holes and web openings (<25 mm diameter) may yield better results. We will investigate this issue further using numerical simulations in the future, in order to evaluate the size effect and the crosstie behavior under impact loadings. Using the finite element method, a three-dimensional model for crossties with different cases of holes and web openings has been calibrated by experimental results from this study [16–22]. The numerical study will enable virtual tests of the crossties with holes and web openings under different limit states (i.e., dynamic and impact conditions due to accidental loading). Our previous work [18] has indicated a relationship between the static and dynamic performance of concrete crossties; it will be further improved to estimate the dynamic capacity of concrete crossties with holes and web openings.

5. Conclusions The holes and web openings undermine the strength, toughness and ductility of railroad concrete crossties. It is essentially important for track and rail engineers to assure that the modification or retrofitting of concrete crossties at construction sites is carried out in a proper manner. Note that existing codes of practice could not accurately estimate such aspects; and they could not portray unforeseen damage or an early warning. From the results obtained in these unprecedented full-scale experiments, it is recommended that transverse holes should be particularly avoided. This is because the transverse hole can reduce almost 20% of the load bearing capacity of the crosstie and such a hole also results in a significant reduction of energy toughness and importantly ductility. This insight into the structural behavior of the concrete crossties with holes and web openings will enable a safer built environment in railway corridors, especially for concrete crossties whose structural inspection is very difficult in practice. Future work includes testing of the dynamic type to evaluate cyclic test behaviors of railway concrete sleepers and to help improve the dynamic finite element modeling outcomes.

Acknowledgments: The authors would also like to thank British Department of Transport (DfT) for Transport - Technology Research Innovations Grant Scheme, Project No. RCS15/0233; and the BRIDGE Grant (provided by University of Birmingham and the University of Illinois at Urbana Champaign). The second author gratefully acknowledges the Japan Society for the Promotion of Science (JSPS) for his JSPS Invitation Research Fellowship (Long-term), Grant No L15701, at Track Dynamics Laboratory, Railway Technical Research Institute and at Concrete Laboratory, the University of Tokyo, Tokyo, Japan. The authors are sincerely grateful to the European Commission for the ﬁnancial sponsorship of the H2020-RISE Project No. 691135 “RISEN: Rail Infrastructure Infrastructures 2017, 2, 3 7 of 8

Systems Engineering Network”, which enables a global research network that tackles the grand challenge of railway infrastructure resilience and advanced sensing in extreme environments (www.risen2rail.eu). Author Contributions: Erosha Gamage and Sakdirat Kaewunruen conceived and designed the experiments; Erosha Gamage and Sakdirat Kaewunruen performed the experiments; Erosha Gamage and Sakdirat Kaewunruen analyzed the data; Alex Remennikov and Tetsuya Ishida contributed reagents/materials/analysis tools; everyone wrote the paper. Conﬂicts of Interest: The authors declare no conﬂict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

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