An experimental and numerical study on the mechanical

Scientia Iranica A (2021) 28(5), 2568{2581

Sharif University of TechnologyScientia Iranica

Transactions A: Civil Engineeringhttp://scientiairanica.sharif.edu

An experimental and numerical study on themechanical behavior of Kunststof Lankhorst Product(KLP) sleepers

M. Siahkouhia, X. Lia, V. Markineb, and G. Jinga;�

a. School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China.b. Department of Engineering Structures, Delft University of Technology, Postbus 5, 2600 AA Delft, the Netherlands.

Received 14 November 2020; received in revised form 14 January 2021; accepted 8 March 2021

KEYWORDSHybrid polymerplastic sleeper;KLP sleeper;Railway ballastedtrack;Dynamic loading;Finite elementmethod;Three bendingmoment test;composite sleeper.

Abstract. In the present paper the mechanical behavior of two types of KunststofLankhorst Product (KLP) sleeper, namely low-density polyethylene sleeper (LDPE-16)and high-density polyethylene sleeper (HDPE-25) with 16 mm and 25 mm steel barsdiameter, are studied. To this end, the static, dynamic, and longtime static three pointsbending moment tests are performed. The HDPE-25 and LDPE-16 with six strain gaugesare mounted on the steel bars to assess their mechanical responses. Moreover, a FiniteElement Method (FEM) model is developed to perform sensitivity analysis on 16 mmHDPE (HDPE-16) and 25 mm LDPE (LDPE-25) based on di�erent steel bar diameters.The results showed that the LDPE-16 steel bar yielded under a load of 30 kN for 4 hours,while HDPE-25 showed signi�cant resistance. Numerical results showed that HDPE-25 isoverdesigned and can be replaced by LDPE-25, which is lighter in weight and lower in price.The natural frequencies of HDPE-25 were almost 16%, 19%, 16%, and 33% higher than thethree �rst bending frequencies and �rst torsion frequency of LDPE-25, respectively. These�ndings prove the better performance of LDPE-25 in the case of preventing resonance. Inaddition, the exural modulus of HDPE-25 was almost 42%, 45%, and 65% higher thanthat of HDPE-16, LDPE-25, and LDPE-16, respectively.© 2021 Sharif University of Technology. All rights reserved.

1. Introduction

Railway track components have been modi�ed overthe years such as ballast particles, fastening systems,and sleepers [1{3]. Railway sleepers are one of theimportant components of the railway track infrastruc-ture. They have an important role in supportingthe rails, providing su�cient horizontal and longitu-

*. Corresponding author. Tel.: +86-159 0117 3048E-mail addresses: [email protected] (M. Siahkouhi);[email protected] (X. Li); [email protected] (V.Markine); [email protected] (G. Jing)

doi: 10.24200/sci.2021.57165.5096

dinal strength, and transferring forces from the railsto the ballast bed [4]. There are several types ofsleepers, the most popular ones are made of timber,steel, and concrete. The timber sleepers have someshortcomings such as biodegradation (timber decay)and vulnerability to �re and insect pests, howeveralways they are welcomed and since a long time theyhave kept their statute in the market [5]. Steelsleepers emerged as a substitute for timber sleepers.They have lighter weight, lower installation costs, andhigher lateral resistance, but there are problems withcorrosion and electrical isolation [6{8]. Compared withtimber sleepers, concrete sleepers, as another alter-native to railway track implementation, can providegreater strength to resist higher axle loads and longer

M. Siahkouhi et al./Scientia Iranica, Transactions A: Civil Engineering 28 (2021) 2568{2581 2569

durability. Jing et al. [9] recommended adding sensorsto concrete sleepers to track the dynamic behaviorof railway tracks. However, this type of sleeper alsohas its limitations in railway track operation, such asheavier weight, high initial cost, lower damping andductility [10{12], and consumption of environmentalnatural resources [13]. Ferdous et al. [14] performeda comprehensive study on composite railway sleepers.Their �ndings show that due to the limited knowledgeon the long-term and mechanical properties of the newcomposite sleepers and alternative materials for timbersleepers, their applications are reduced.

The history of the application of timber sleeperscan be traced back to more than 150 years ago [15].Currently, about 2.5 billion sleepers are used in railwaynetworks in the world [16]. Timber sleepers havebeen used in the railway industry for a long time,especially in the United States [17] and Australia [18].Several studies have evaluated the dynamic and staticperformance of timber sleepers [19{21]. Sadeghi andBarati [22] studied the performance of timber sleepersin a three bending test. The results showed that thetimber sleeper de ection under a load of 30 kN inthe middle of the sleeper was about 4.2 mm. Songet al. [23] investigated the pressure distribution oftimber sleepers under cyclic loading. Their �ndingsshowed that under a cyclic load of about 40 kN, thetimber sleeper faced a maximum pressure of about0.13 MPa in the middle of the sleeper. Several majorfailure causes of timber sleepers such as fungal decay,end splitting, and termite attack were proposed byFerdous and Manalo [24]. These causes of damage havebeen treated with toxic chemicals to destroy harmfulorganisms in the timber, and plates have been installedat the ends of the timber sleepers to minimize theirseparation. Figure 1 shows some common defects oftimber sleepers. Recently, due to lighter weight, higherthermal and electrical conductivity, higher corrosionresistance, damping ratio, and durability, composite

Figure 1. The timber sleepers defects mostly are seen inthe �eld due to the (a) environmental e�ects and (b)overloading (Photo credit: G. Jing).

sleepers have been increasingly used [25{27]. Accordingto their geometric and mechanical properties, com-posite sleepers are mostly considered substitutes fortimber sleepers, especially in key areas where dampingand ductility characteristics are more required, suchas turnouts [28], bridges [29,30], and tunnels [31].Recently, a new generation of Kunststof LankhorstProduct (KLP) type of steel bar sleepers has beenput on the market, which has su�cient mechanicalproperties to withstand high train axle loads. Thesesleepers have better elasticity, a low ballast abrasionindex relative to the elastic contact between sleepersand ballast particles, and higher rail track lateral andlongitudinal stability [32]. In addition, they providehigher durability, easier transportation and installa-tion, and sustainability in solid waste plastic materials.These sleepers are based on a polymer matrix andare usually made of recycled plastic. The well-knownavailable products are TieTek [33], Axion [34] andKLP [35] (see Figure 2). This kind of sleeper stillneeds more investigation; however, some studies havebeen conducted on this topic. In the ISO standard [36],the plastic sleepers are categorized into three materialtypes of A, B, and C, based on the track operationalfeatures such as train axle load and speed. Theproperties provided by material type A are similar tothe properties of tropical hardwood sleepers, used forballastless track and special railway track operations,with maximum axle loads of 200 kN and 140 kN fortrain speeds of 130 km/h and 300 km/h, respectively.Material type B is equivalent to timber sleepers for UIC5/6 track categories, with a maximum 225 kN axle loadfor a train speed of 160 km/h, and material type C isequivalent to hardwood sleeper for the heavy-haul trackwith a maximum axle load of 350 kN for a train speedof 80 km/h.

In Table 1 [36], some mechanical properties of

Figure 2. Cross-section of Kunststof Lankhorst Product(KLP) sleepers High-Density Polyethylene (HDPE): (a)Without steel bar, (b) with steel bars, (c), and (d) Tieteksleeper used in China (photo credit: G. Jing).

2570 M. Siahkouhi et al./Scientia Iranica, Transactions A: Civil Engineering 28 (2021) 2568{2581

Table 1. Mechanical properties of plastic sleepers according to ISO standard [36].

EN ISOstandard

Bending strength(MPa)

Flexural modulus(MPa)

Shear strength(MPa)

Longitudinal compressionstrength (MPa)

Type A � 28 � 6000 � 7 � 40

Type B � 18 � 2500 � 4:5 � 8

Type C � 13:8 � 1170 | |

a plastic sleeper for adoption in the industry arepresented based on ISO standards. Lampo et al. [37]discussed the requirement to use KLP sleepers as analternative to timber sleepers in the United States.A bending test was performed on a High-DensityPolyethylene (HDPE) sleeper with a 25 mm steelbar, the results showed that the ultimate strengthof the sleeper exceeded 31 MPa. In a study doneby the Transportation Technology Center [38], thee�ect of temperature on the railway track verticalsti�ness which has plastic sleepers was quanti�ed.The measurement data showed that the vertical trackmodulus with plastic sleeper was comparable to thatwith oak-wood sleeper and was not signi�cantly af-fected by the change of temperature within the rangeof 57 degrees in the environment and 88 degrees inthe center of the sleeper [38]. The Federal RailroadAdministration (FRA) [39] conducted a series of teststo address the e�ects of temperature and fasteningsystems on the cracking and impact properties ofplastic sleepers. It was found that compared tothe test performed at ambient and high temperature,during the low-temperature test, the increase of thesti�ness of the sleeper was signi�cantly higher. Thetest results showed that the fastening system couldcause a signi�cant reduction of resistance of the sleeper.The mechanical properties of Glass Fiber ReinforcedPolymer (GFRP) sleepers made of thermoplastics andcontinuous glass �bers were studied by Vijay et al. [40].Fatigue test, nail pull test and �eld test were carried outin this research. The results showed that the strengthand fatigue resistance of these sleepers were similarto those of timber sleepers. The behavior and long-term performance of the entire rail system with HDPEsleepers were studied by Lotfy and Issa [41], using staticand cyclic test methods. The results of this studyshowed the behavior of HDPE sleepers under fatigueloading, normal wear, and minimal degradation.

Considering low fatigue strength, environmentalissues resulting in a sharp reduction in forest resources,increasing train axle loads and speeds, timber sleepersmay not be an available option for railway tracksconstruction. As is evident from literature, so far thestatic and dynamic behavior of the new generation ofKLP sleepers with steel bars had not been investigated,while this subject is very important in the areas relatingto railway tracks and modeling their behavior. In

addition, Finite Element Method (FEM) modelingof KLP sleepers is needed to conduct more researchon this new type of sleepers. Therefore, in threebending moment tests in the Mechanical Laboratoryof TU Delft, two types of KLP sleepers includingHDPE-25 and LDPE-16 have been studied for railwaytracks. They were investigated by performing static,dynamic, and longtime exural tests. Six strain gaugeswere mounted inside of each of these two sleepers tostudy the yield behavior of steel bars in the longtimebending moment test. Sensitivity analysis has beenperformed to check the diameter of other steel bars ofHDPE and LDPE to meet the structural and economicoptimization requirements of these sleepers. Therefore,HDPE-16 and LDPE-25 are also considered for thefurther analysis of mechanical behavior.

2. Material properties of KLP sleepers

Lankhorst Moldings Sneek-Holland [42] designed twomore durable reinforced plastic sleepers, namely HDPEsleeper and LDPE sleeper, with reinforcing steel bardiameters of 25 mm and 16 mm, respectively. Thereare some di�erences between HDPE and LDPE typeKLP sleepers. The LDPE has four reinforcementsteel bars with a diameter of 16 mm, made of low-density polyethylene recycled plastic. The HDPE hasfour 25 mm reinforcement steel bars and is madeof high-density polyethylene recycled plastic. Giventhat LDPE has lower price, weight, and mechanicalproperties, it is recommended to use these two typesfor railway tracks (Type B). The characteristics of thesetwo types of KLP sleepers are presented in Table 2.

3. Experimental study

3.1. Bending moment testOne of the criteria for evaluating the sleepers is themaximum bearing loading level which produces the�rst crack identi�ed by operators using portable mi-croscopes [42]. This method is mostly used for con-crete sleepers based on AS1085.14-2009 [43], AREMA2017 [44], TB/T 1879-2002 [45] and UIC-713R [46].In this research, a bending test is performed basedon the ISO standard for plastic sleepers [36]. TwoHDPL/LDPE sleepers are manufactured, and six straingauges are mounted on the steel bars to study their ex-


Table 2. Characteristics of Kunststof Lankhorst Product (KLP) sleepers including HDPL/LDPE.

Sleeper typeSteel bars

Dimension(mm)

Bendingmodulus(MPa)

Diameter(mm)

Type Min. plasticcover (mm)

HDPE 25 S235 15 250 � 150 � 2500 650{1250LDPE 16 12 250{400

ural strength properties [47]. Both KLP sleepers haveundergone static, dynamic, and long-term static 3-point bending tests. During the tests, a metal rod is in-stalled as the reference of zero point, and the de ectionis measured by the displacement of the center of thebeam relative to the reference rod using a displacementsensor of the Linear Variable Di�erential Transformer(LVDT) as can be seen in Figure 3. The actuator isloaded in the center of the sleeper, about 1250 mmfrom the end, and the sleeper rested on two supportsthat were nearly 1500 mm apart from each other.

Figure 4 shows that the six strain gauges aremounted at 400 mm (1/6 sleeper length), 900 mm (1/3sleeper length), and 1250 mm (the sleeper center) fromthe left side of the sleeper on the steel bars at thetop and bottom of sleeper. The strain gauges wereconnected to a data logger through wires, as shownin Figure 4. The strain gauges are produced by TML

and are suitable for steel, and the data logger is TMRproduced by TML.

3.1.1. Static bending moment testThree static 3-point bending tests were performed onboth H/LDPE sleepers with di�erent loading speeds.The sleeper was loaded with a preload of 2 kN, andthen the load was increased at three speeds of 0.5 kN/s,1 kN/s, and 2 kN/s. The load reached its maximumvalue when the sleeper failed and then decreased to the2 kN loading level at the same loading speed. Thenthe maximum load of H/LDPE is used in Eq. (1) tocalculate exural strength (MPa) of sleepers (�f ) andcompare it with ISO standard (Table 1). Eq. (1) canbe expressed as follows:

�f =3FL2bh2 ; (1)

where F , L, b, and h represent maximum applied load

Figure 3. An overview of experimental test including: (a) Placement of sleeper and (b) Linear Variable Di�erentialTransformer (LVDT) location.

Figure 4. Location of strain gauges in sleepers body and unit (cm).


Figure 5. (a) Static, (b) dynamic, and (c) longtime static bending tests of HDPE-25.

(N), span of supports (mm), sleeper width (mm), andsleeper height (mm), respectively.

3.1.2. Dynamic bending moment testThe dynamic 3-point bending tests were carried out onboth H/LDPE sleepers. The dynamic loading had acyclic load between 3 kN and 30 kN which was appliedto the sleeper at a frequency of 5 Hz.

3.1.3. Longtime static bending moment testA longtime static test was also performed on bothH/LDPE sleepers. A load of 30 kN was applied for4 hours. After 4 hours, the entire load was completelyunloaded, and then the measurement continued for 12hours This measurement was recorded with a samplingfrequency of 0.1 Hz.

3.1.4. Results and discussionAs shown in Figure 5(a) the minimum speed of loadinghad a maximum de ection of 4.2 mm. Also, it canbe seen that after unloading, the de ection of HDPE-25 returned to its original position. However, a littleamount of de ection remained in middle of HDPE-25as about 0.3 mm. In Figure 5(b), the 5 Hz cyclic loadwas applied in a 3-point bending test to the HDPE-25. From 3.2 mm at the beginning of the �rst cycle to3.5 mm at the last cycle of loading, a slight increasein de ection can be seen. It can be seen that thede ection of the sleeper returned to the �rst positionwith slight plastic deformation of 0.1 mm. Figure 5(c)shows the results of the 4-hour static 3-point bendingmoment test of the HDPE-25. The de ection value ofthe longtime test is considerably greater than those ofthe static and dynamic tests. The plastic deformationvalue after unloading was also higher at 0.5 mm, whichindicates that the strength against fatigue loads waslower compared to the previous static and dynamictests. As shown in Figure 6, the strains of the HDPE-25 can be seen during the 4-hour static 3-point bendingmoment test. This shows that strain gauges mountedcloser to the loading zone of the sleeper measured morestrains. C1 strain gauge detected the maximum strainvalue of 1000 �e, which is followed by B1 with 600 �e.These strain gauges were located at the bottom of theloaded part of the sleeper where steel bars were under

Figure 6. Strains of longtime static 3-point bending testfor HDPE-25.

signi�cant tensile stresses. Other strain gauges did notexperience high tensile or compressive stresses due tothe high resistance of the sleeper against the 30 kNloading level.

Figure 7(a) shows the results of the static 3-pointbending moment test of the LDPE-16. As expected,the lower loading speed (0.5 kN/s loading speed)resulted in a higher de ection of 8.7 mm. Figure 7(b)shows the 5 Hz dynamic 3-point bending moment testof the LDPE-16. As the cyclic loading time increased,the de ection of sleeper increased slightly, from 6.8 mmin the �rst cycle to 7.2 mm in the last cycle. Figure 7(c)shows the 4-hour static 3-point bending moment testof the LDPE-16 sleeper. Compared with HDPE-25and the other two static and dynamic tests, it showedgreater de ection, which means that the sleeper had alower strength against fatigue loads.

As shown in Figure 8, the strains can be seenduring the 4-hour static 3-point bending moment testof the LDPE-16. The strain gauge C1, which was underforce, showed a larger strain compared to other gauges.There was a peak in the strain of C1 from {2000 �e to{2500 �e; it shows that the steel bar yields due to the30 kN load applied for around three and half hours.

After calculating the exural strength of the twotypes of HDPE-25 and LDPE-16, they were foundto be 28 MPa and 20 MPa, respectively. Therefore,both HDPE-25 and LDPE-16 can be used based onstandards (� 18 MPa); however, considering longtimestatic test, LDPE-16 failed and cannot be used. Whenthe LDPE-16 was loaded with 30 kN for a long time (4-hour), the reinforcing steel bar yielded, therefore, theLDPE-16 did not meet the standard requirement. Thecomparison of the exural strength of KLP sleepers and


Figure 7. (a) Static, (b) dynamic, and (c) longtime static bending tests of LDPE-16.

Figure 8. Strains of longtime static 3-point bending testfor LDPE-16.

timber sleepers showed that the hardwood-oak sleepershad a moderate bending strength of 41 kN [22], whichmeans that it was almost 40% lower than HDPE-25and 15% higher than LDPE-16.

3.2. Impact hammer testThe impact hammer test is performed on HDPE-25as the most commonly used plastic sleeper to showthe natural frequencies of the sleeper and validate thenumerical modeling results of the frequency analysis.This sleeper has been chosen because it can pass allmechanical tests. Through performing the impacthammer test and using ten accelerometers which wereinstalled on the HDPE-25 at a distance of 275 mm fromeach other, the natural frequencies are obtained [48].The natural frequencies of sleepers are important forthe development of a real dynamic model of railwaytracks and sleeper itself, which can predict its dynamicresponses. Impact hammer test is one of the popularmethods for doing modal analysis of structures [49{51]. For preparing the free-free condition, the sleeperwas placed on two wooden blocks at both ends. Theimpacts were applied in three places, as can be seen inFigure 9. Impacts are applied �ve times at each loca-tion, to prevent errors in the measurement. The resultswere incorporated in the Matlab program [52]. UsingFast Fourier Transformer (FFT), the accelerations wereconverted to the frequency domain to obtain dominantfrequencies of HDPE-25 [29].

The calculation of dominant frequencies HDPE-25 is shown in Figure 10. The results showed that the�rst, second, and third natural frequencies of HDPE-25were close to 37.5 Hz, 156.3 Hz and 237.5 Hz, respec-tively. These results are used for the validation of fre-quency analysis in FEM sensitivity analysis. As shown

Figure 9. Con�guration of sensors and impacts on theHDPE-25 sleeper.

in Figure 10, the dominant frequencies of timber andHDPE sleeper are calculated. It is concluded that the�rst dominant frequency of HDPE-25 as 37.5 Hz hasan almost 35% di�erence compared to that of timberas 57.2 Hz. It is worthy of consideration that the ampli-tude of timber sleeper frequencies was about ten timesthat of HDPE which shows the better performance ofHDPE sleeper in damping of vibrations. According tothe results of modal analysis, the damping ratio of KLPsleepers was 0.34, which was nearly 8% higher than thedamping ratio of timber sleepers of 0.31.

4. Sensitivity analysis

4.1. FEM model developmentTo analysis the behavior of H/LDPE sleepers, numer-ical modeling is developed. The steel bars con�gu-rations can be seen in Figure 11. There were foursteel bars at the four corners of the sleepers. TheHex mesh was chosen for the discretization of eachinstance. The mesh size of steel bars and sleepers was50 cm and 10 cm, respectively. A mesh size analysiswas performed to check the �ner mesh sizes of the�nal results. A static load with a loading rate of 2kN/s is applied to the sleepers at the middle point.For boundary conditions, sleepers rested as simplysupported beams. This section aims to categorize theapplication of four sleepers including HDPE-25, LDPE-16, HDPE-16, and LDPE-25 based on the numericalstudy.

4.2. Model validationTo validate the numerical model through experiment, a


Figure 10. Dominant frequencies of (a) HDPE-25 and (b) timber sleeper in free vibration analysis.

Figure 11. Steel bars con�guration for Kunststof Lankhorst Product (KLP) sleepers: (a) H/LDPE-25 and (b)L/HDPE-16.

Figure 12. An overview of three bending moment tests of Kunststof Lankhorst Product (KLP) sleepers.

static bending test is considered as shown in Figure 12.In the experimental study, the loading rate of thenumerical model and the loading speed of 2 kN/s wereselected. It can be seen from Figure 13 that thede ections of the H/LDPE sleepers in the numericalsimulation were almost the same as the maximumde ection obtained through the experimental results.The di�erence between the maximum de ection ofHDPE and LDPE between numerical modeling andexperimental e�ort was 4% and 2%, respectively.

4.3. Natural frequencies of KLP sleepersTo plot the mode shapes of the sleeper and comparethem with the experimental results, modal analysis isdeveloped using numerical modeling. It can be seenfrom Table 3 that the frequencies of the numericalmodel of HDPE-25 were almost the same as the �rst,second, and third natural frequencies obtained throughthe experiment. This can be taken as a shred of strongevidence ensuring the validity of HDPE-25 vibrationalproperties in the numerical model. A further frequency


Table 3. Natural frequencies and mode shapes of four di�erent Kunststof Lankhorst Product (KLP) sleepers.

Mode shape no.Natural frequencies (Hz) Mode shapes

HDPE-25 LDPE-16 HDPE-16 LDPE-25

1st bending mode shape 37 24 28.5 31

2nd bending mode shape 155.8 122.14 150.19 125.67

3rd bending mode shape 236 193.42 234.74 196.92

4th bending mode shape 366 323 353 335

5th bending mode shape 469 426 451 441

1st torsion mode shape 60.23 44.4 61 40.31

Figure 13. Validation of Finite Element Method (FEM) results with bending moment test of sleepers: (a) HDPE and (b)LDPE.


analysis was performed to compare the natural frequen-cies of H/LDPE-25 and L/HDPE-16. The results showthat in the �rst bending mode shape that the steel baris directly engaged in deforming, the higher diameterof the steel bar shows higher natural frequencies asthe highest belongs to HDPE-25 as 37 Hz, which isfollowed by 31 Hz, 28.5 Hz, and 24 Hz of LDPE-25,HDPE-16 and LDPE-16, respectively. From the secondto �fth mode shapes, higher frequencies also belongto HDPE-25 and 16. In the torsional mode, only thematerial type was e�ective for the performance of thesleepers, because these sleepers did not have stirrupsfor restraining the steel bars. As can be seen, HDPE-25 and 16 had higher frequencies than LDPE-16 and 25due to higher mechanical properties. Considering theactuation frequencies of railway track due to dynamicloads which are mostly in the range of 200 Hz to300 Hz [3,53], it is better that the sleeper's frequencybe kept out of this frequency range to avoid trackresonance. Therefore, HDPE-25 shows the closest,and LDPE-16 shows the furthest frequencies from thisfrequency range compared with other KLP sleepers.

4.4. Maximum stresses of KLP sleepersISO standard [36] provides guidelines for calculatingreference test loads for plastic sleeper types. A threebending moment test is simulated, and the results arereported in the following sections. A static load with aloading speed rate of 2 kN/s is applied to the sleepers,and the corresponding stresses are presented. Table 4shows the material properties used in the model. Thesleeper is modeled as a simply supported beam with adistance of 1500 mm between the supports.

The validated models based on the maximumde ection of sleepers are used for presenting the cor-responding stresses of H/LDPE sleepers. As shownin Figure 14, the maximum stresses of both H/LDPEsleepers appeared on steel bars, which means thatthe maximum stress is transferred to the steel bars,resulting in less stress on the composite.

As is clear from Figure 15, the maximumstress in the HDPE-25 and LDPE-25 steel bars were0.13 GPa and 0.19 GPa, respectively, with almost30% di�erence; while the corresponding stresses in thecomposite were around 5.22 MPa and 5.3 MPa withalmost 1% di�erence. This di�erence shows that the

identical steel bars banned stresses to be transferredto composite, while LDPE-25 steel bars underwenthigher stresses. For HDPE-16 and LDPE-16, themaximum stresses transferred to the composites wereabout 4 MPa and 3.3 MPa, respectively, expressinga di�erence of about 17%, while the maximumstresses transferred to the steel bars were 0.2 GPaand 0.15 GPa, respectively, expressing a di�erenceof nearly 25%. Due to the smaller diameter andresistance of the 16 mm steel bar, a certain degree ofstress is transferred to the composite material, whichcould fail under high load and long-term use.

Figure 16 shows the yield zone of steel bars foreach sleeper. HDPE-25 had higher exural strength,about 68 kN, which shows that the design is relativelyoverdesigned and is not economically acceptable. The exural strength of LDPE-16 was lower than that ofits counterparts which was 35 kN. Two other newdesigns (HDPE-16 and LDPE-25) based on sensitivityanalysis studies showed exural strengths of 33 kN and63 kN, respectively. Therefore, it can be concludedthat LDPE-25 can be a substitution for HDPE-25 inrailway tracks with lower weight and price but almostthe same exural strength.

4.5. Bending modulus calculationThe bending modulus represents the ratio of stress tothe corresponding strain of the material within the elas-tic region. Sti� materials demonstrate a high modulusand ductile materials exhibit a low modulus. In thisstudy bending modulus for all four designed sleeperswere calculated using FEM results and Eq. (2) based onASTM D790 standard [54]. Figure 17 shows the bend-ing modulus values of HDPE-25/16 and LDPE-25/16.

E =L3F

4wh3d; (2)

where w, h, L, d, and F represent the width andheight of the sleeper, the distance between the twoouter supports, and the de ection and the load appliedat the middle of the sleeper.

The maximum bending modulus of HDPE-25 wasalmost 0.6 MPa, followed by HDPE-16, LDPE-25, andLDPE-16, which had maximum bending modulus val-ues of 0.32 MPa, 0.3 MPa, and 0.2 MPa, respectively.The bending modulus HDPE-25 was almost 42%, 45%,

Table 4. Material properties of H/LDPE sleepers used in Finite Element Method (FEM) modeling of bending momenttest.

Sleeper propertiesDensity(kg/m3)

Elastic modulus(MPa)

Poisson's ratioPlasticity modulus

(MPa)

Composite HDPE 870 800 0.4 |LDPE 870 325 0.4

Steel bars 7850 210000 0.3 235


Figure 14. Stress distribution (Pa) of the center bending test of sleepers and steel bars for HDPE-25; LDPE-16;HDPE-16; and LDPE-25.

and 65% higher than HDPE-16, LDPE-25 and, LDPE-16, respectively.

5. Conclusions

Increasing axle loads and train speeds have motivatedresearchers and track owners to consider designing newtypes of sleepers. Recently, several composite sleepers

have been developed worldwide; however, new typessuch as Kunststof Lankhorst Product (KLP) sleepershave emerged. Especially with the development ofrailway tracks using timber sleepers, the track com-ponents will be subject to greater dynamic impacts,thereby accelerating degradation and shortening theservice life. Considering the limitations of the use oftimber sleepers, it has become crucial to produce a new


Figure 15. (a) Maximum stress of KLP sleepers in composite. (b) Maximum stress of Kunststof Lankhorst Product(KLP) sleepers in steel bars.

Figure 16. Load-center displacement relationship forKunststof Lankhorst Product (KLP) sleepers.

Figure 17. Bending modulus values based on FiniteElement Method (FEM) results for HDPE-25&16 andLDPE-25&16 sleepers.

generation of KLP sleepers equipped with steel barsthat provide greater damping and higher mechanicalproperties. In this study, the mechanical behavior ofHDPE-25 and LDPE-16 as two current KLP sleeperswere studied and numerical modeling is accordinglydeveloped to analyze the behavior of HDPE-16 andLDPE-25. The �ndings of the current study can besummarized as follows:

1. HDPE-25 and LDPE-16 sleepers showed poor bend-ing resistance to long-term static loading under

a 4-hour load of 30 kN, and their de ection wasrelatively large, about 5.75 mm and 11.7 mm,respectively. Strain results of steel bars in themiddle of sleeper under bending load showed thatthe steel bars of LDPE-16 yielded under 30 kN loadin a longtime static test;

2. The natural frequencies of HDPE-25 were 37 Hz,155.8 Hz, 236 Hz, and 60.23 Hz. As is evident fromthese �ndings, the HDPE-25 natural frequencieswere higher than those of its counterparts. The con-ventional actuation frequencies of the train wheelsare in the range of 200 Hz to 300 Hz, while inthe present study, it is observed that the naturalfrequencies of LDPE-25 were 31 Hz, 125.67 Hz,169.92 Hz, and 40.31 Hz. These �ndings revealthe signi�cant di�erence between the conventionalactuation frequencies of the train wheels and thenatural frequencies of LDPE-25;

3. According to numerical bending test results,HDPE-25 had higher exural strength around68 kN. The exural strength of LDPE-16 (35 kN)was lower than other exural strengths. Two othernew designs of HDPE-16 and LDPE-25 based on thesensitivity analysis study showed exural strengthsof 33 kN and 63 kN, respectively. Therefore, replac-ing HDPE-25 with LDPE-25 can be cost-e�ectiveand ensure more e�ciency in terms of weight, whileit can provide the same degree of exural strengthas provided through using its counterpart;

4. The maximum stresses of HDPE-25 and LDPE-25 steel bars were 0.13 GPa and 0.19 GPa, re-spectively, with a di�erence of nearly 30%; whilethe corresponding stresses in the composite wereabout 5.22 MPa and 5.3 MPa, with a di�erenceof nearly 1%. This di�erence indicates that thesame steel bars banned stresses to be transferredto composite materials, but LDPE-25 steel barsmust withstand higher stresses. For HDPE-16and LDPE-16, the maximum stresses in compositeswere around 4 MPa and 3.3 MPa, respectively,showing a di�erence of about 17%, while in the


steel bars, the stresses were 0.2 GPa and 0.15 GPa,showing a di�erence of nearly 25%. Due to thelower diameter and resistance of 16 mm steel bars,a certain degree of stress is transferred to thecomposite, therefore the steel bars with 16 mmdiameter are not suitable for KLP sleepers forType B railway tracks;

5. HDPE-25 had maximum bending modulus withalmost 0.6 MPa followed by HDPE-16, LDPE-25,and LDPE-16 with maximum bending modulusvalues of 0.32 MPa, 0.3 MPa, and 0.2 MPa, respec-tively. The bending modulus HDPE-25 was almost42%, 45%, and 65% higher than that of HDPE-16,LDPE-25, and LDPE-16, respectively.

Acknowledgment

This paper has been supported by the ChinaAcademy of Railway Science Foundation (Grant No.2018YJ043). The authors would like to thankLankhorst for providing test samples and �nancialsupports.

References

1. Esmaeili, M., Zakeri, J.A., Kaveh, A., Bakhtiary, A.,and Khayatazad, M. \Designing granular layers forrailway tracks using ray optimization algorithm", Sci.Iran., 22(1), pp. 47{58 (2015).

2. Zakeri, J.A. and Hassanrezaei, H. \Experimental inves-tigation on e�ect of winged sleeper on lateral resistanceof ballasted track", Sci. Iran., A, 28(2), pp. 656{665(2021).

3. Jing, G., Wang, J., Wang, H., and Siahkouhi, M.\Numerical investigation of the behavior of stoneballast mixed by steel slag in ballasted railway track",Constr. Build. Mater., 262, p. 120015 (2020).

4. Zhao, J., Chan, A.H.C., and Burrow, M.P.N. \Reli-ability analysis and maintenance decision for railwaysleepers using track condition information", J. Oper.Res. Soc., 58(8), pp. 1047{1055 (2007).

5. Sadeghi, J. \Field investigation on vibration behaviorof railway track systems", International Journal ofCivil Engineering, 8, pp. 232{241 (2010).

6. Hill, K. and Relph, S., Corus UK Ltd, Steel railroadsleepers U.S. Patent 6,230,981 (2001).

7. Mitchell, R., Baggott, M. G., and Birks, J. \Steelsleepers-an engineering approach to improved produc-tivity", Conf. Railw. Eng. 1987 Prepr. Pap., Institu-tion of Engineers, Australia, p. 131 (1987).

8. Jing, G., Fu, H., and Aela, P. \Lateral displacementof di�erent types of steel sleepers on ballasted track",Constr. Build. Mater., 186, pp. 1268{1275 (2018).

9. Jing, G., Siahkouhi, M., Edwards, J.R., Dersch, M.S.,and Hoult, N.A. \Smart railway sleepers-a review of re-cent developments, challenges, and future prospects",Constr. Build. Mater., p. 121533 (2020).

10. Manalo, A., Aravinthan, T., Karunasena, W., andTicoalu, A. \A review of alternative materials forreplacing existing timber sleepers", Compos. Struct.,92(3), pp. 603{611 (2010).

11. Zakeri, J.A. and Bakhtiary, A. \Comparing lateralresistance to di�erent types of sleeper in ballastedrailway tracks", Sci. Iran., 21(1), pp. 101{107 (2014).

12. Jing, G.Q., Aela, P., Fu, H., and Yin, H. \Numericaland experimental analysis of single tie push testson di�erent shapes of concrete sleepers in ballastedtracks", Proc. Inst. Mech. Eng. Part F J. Rail RapidTransit, 233(7), pp. 666{677 (2019).

13. Li, B., Li, H., Siahkouhi, M., and Jing, G. \Studyon coupling of glass powder and steel �ber as silicafume replacement in ultra-high performance concrete:concrete sleeper admixture case study", KSCE J. Civ.Eng., 24, pp. 1545{1556 (2020).

14. Ferdous, W., Manalo, A., Van Erp, G., Aravinthan,T.,Kaewunruen, S., and Remennikov, A. \Compositerailway sleepers-Recent developments, challenges andfuture prospects", Compos. Struct., 134, pp. 158{168(2015).

15. Adams, J.C.B. \Cost e�ective strategy for track sta-bility and extended asset life through planned timbersleeper retention", Conf. Railw. Eng. 1991 DemandManag. Assets; Prepr. Pap., Institution of Engineers,Australia, p. 145 (1991).

16. Ferdous, W., Manalo, A., Van Erp, G., Aravinthan,T., and Ghabraie, K. \Evaluation of an innovativecomposite railway sleeper for a narrow-gauge trackunder static load", J. Compos. Constr., 22(2), p.4017050 (2018).

17. Rothlisberger, E. \History and development of woodensleeper", Website: < http://www. corbat-holding.ch/documents/showFile.asp> (2008).

18. Manalo, A., Aravinthan, T., Karunasena, W., andTicoalu, A. \A review of alternative materials forreplacing existing timber sleepers", Composite Struc-tures, 92(3), pp. 603{611 (2010).

19. Yella, S., Dougherty, M., and Gupta, N.K. \Conditionmonitoring of wooden railway sleepers", Transp. Res.part C Emerg. Technol., 17(1), pp. 38{55 (2009).

20. Zakeri, J. and Bakhtiary, A. \Comparing lateral resis-tance to di�erent types of sleeper in ballasted railwaytracks", Scientia Iranica, 21, pp. 101{107 (2014).

21. Thompson, D.J. and Verheij, J.W. \The dynamicbehaviour of rail fasteners at high frequencies", Appl.Acoust., 52(1), pp. 1{17 (1997).

22. Sadeghi, J. and Barati, P. \Comparisons of themechanical properties of timber, steel and concretesleepers", Struct. Infrastruct. Eng., 8(12), pp. 1151{1159 (2012).

23. Song, W., Huang, B., Shu, X., Str�ansk�y, J., and Wu,H. \Interaction between railroad ballast and sleeper:a DEM-FEM approach", Int. J. Geomech., 19(5), p.4019030 (2019).


24. Ferdous, W. and Manalo, A. \Failures of mainline rail-way sleepers and suggested remedies-review of currentpractice", Eng. Fail. Anal., 44, pp. 17{35 (2014).

25. GangaRao, H.V.S., Taly, N., and Vijay, P.V., Rein-forced Concrete Design with FRP Composites, CRCpress (2006).

26. Ferdous, W., Manalo, A., Khennane, A., and Kayali,O. \Geopolymer concrete-�lled pultruded compositebeams-concrete mix design and application", Cem.Concr. Compos., 58, pp. 1{13 (2015).

27. Ferdous, W., Khennane, A., and Kayali, O. \Hy-brid FRP-concrete railway sleeper", 6th InternationalACIC Conference, Queen's University Belfast, Septem-ber 10-12 (2013).

28. Jing, G., Siahkouhi, M., Qian, K., and Wang, S.\Development of a �eld condition monitoring systemin high speed railway turnout", Measurement, 169, p.108358 (2020).

29. Esmaeili, M. and Siahkouhi, M. \Tire-derived aggre-gate layer performance in railway bridges as a novelimpact absorber: Numerical and �eld study", Struct.Control Heal. Monit., 26(10), p. e2444 (2019).

30. Esmaeili, M., Ataei, S., and Siahkouhi, M. \A casestudy of dynamic behaviour of short span concrete slabbridge reinforced by tire-derived aggregates as sub-ballast", Int. J. Rail Transp., 8(1), pp. 80{98 (2020).

31. Wang, G.W. \Properties and utilization of steel slag inengineering applications", Wollongong, Ph. D. Thesis,University of Wollongong (1992).

32. Jing, G. and Aela, P. \Review of the lateral resistanceof ballasted tracks", Proc. Inst. Mech. Eng. Part F J.Rail Rapid Transit, 234(8), pp. 807{820 (2020).

33. Tietak, \Composite sleeper", http://www.tietek.net./.34. A xion-EcoTrax \ECOTRAXr axion composite

sleeper mechanical properties", %3Cwww.axionintl.com%3E.

35. KLP, Lankhorst Rail and Netherlands, \KLPrhybrid polymer sleepers - corporate brochure",%3Cwww.lankhorstrail.com%3E.

36. Standard, I. \Plastics { Plastic railway sleepers forrailway applications (railroad ties)", ISO 12856 (2014).

37. Lampo, R., Nosker, T., and Sullivan, H. \Devel-opment, testing and applications of recycled plasticcomposite cross ties", US Army Eng. R&D Cent.(2003).

38. Jimenez, R., Vertical Track Modulus in Plastic Com-posite Tie Test Zones at FAST, Transportation Re-search Board (TRID), DOT/FRA/ORD-03/13 (2003).

39. Rei�, R. and Trevizo, C., Cracking and ImpactPerformance Characteristics of Plastic CompositeTies., United States, Federal Railroad Administration(2012).

40. Vijay, P.V., Hota, G.V.S., Bethi, A., Chada, V., andQureshi, M.A.M. \Development and implementationof recycled thermoplastic RR ties", Jt. Rail Conf., pp.209{218 (2010).

41. Lotfy, I. and Issa, M.A. \Evaluation of the longitudinalrestraint, uplift resistance, and long-term performanceof high-density polyethylene crosstie rail support sys-tem using static and cyclic loading", Proc. Inst. Mech.Eng. Part F J. Rail Rapid Transit, 231(8), pp. 835{849(2017).

42. Moulding, L. \Sustainable plastic sleeper", https://www.lankhorst-mouldings.com/.

43. Murray, M.H. and Bian, J. \Ultimate limit statesdesign of concrete railway sleepers", Proc. Inst. Civ.Eng., Thomas Telford Ltd, pp. 215{223 (2012).

44. Arema, L.M.D. \American railway engineering andmaintenance-of-way association", Man. Railw. Eng., 2,pp. 55{57 (2013).

45. \Static load crack resistance test method for pre-stressed concrete sleepers (TB/T 1879-2002)", Minist.Railw. (Q72), Academy of Railway Sciences, Instituteof Railway Construction (2002).

46. Anurag, S. \Problems in maintenance of Indian railwayin deserts and possible solutions", UIC Work. DesertRailw., pp. 67{82 (2008).

47. Luuk van der Drift, V.M. \3- and 4-point bending testof a plastic sleeper" (2018).

48. Silva, �E.A., Pokropski, D., You, R., and Kaewun-ruen, S. \Comparison of structural design methods forrailway composites and plastic sleepers and bearers",Australian Journal of Structural Engineering, 18(3),pp. 160{177 (2017).

49. Lam, H.F. and Wong, M.T. \Railway ballast diagnosethrough impact hammer test", Procedia Eng., 14, pp.185{194 (2011).

50. Kaewunruen, S. and Remennikov, A.M. \Impact ca-pacity of railway prestressed concrete sleepers", Eng.Fail. Anal., 16(5), pp. 1520{1532 (2009).

51. Kaewunruen, S. and Remennikov, A.M. \Progressivefailure of prestressed concrete sleepers under multiplehigh-intensity impact loads", Eng. Struct., 31(10), pp.2460{2473 (2009).

52. Brandt, A., Noise and Vibration Analysis: SignalAnalysis and Experimental Procedures, John Wiley &Sons (2011).

53. An, B., Gao, L., Xin, T., Xiang, G., and Wang, J.\A novel approach of identifying railway track rail'smodal frequency from wheel-rail excitation and itsapplication in high-speed railway monitoring", IEEEAccess, 7, pp. 180986{180997 (2019).

54. ASTM, C. ASTM Standards, American Society forTesting Materials Philadelphia (1958).

Biographies

Mohammad Siahkouhi is currently a Doctoral stu-dent at the Department of Civil Engineering, BeijingJiaotong University. He obtained a master of sciencein Railway Engineering from the Iran University ofScience and Technology. His research interest includes


railway engineering, concrete technology, compositestructures, and structural health monitoring.

Xinjie Li received her BSc degree in Civil Engineeringfrom Beijing Jiaotong University, Beijing, China, in2019. She is currently an MSc student in RailwayEngineering, Beijing Jiaotong University. Her researchinterests include analysis of railway track structureand the application of composite materials on therailway track structure.

Valerie Markine obtained his MSc Diploma in Me-chanics from Gorky State University, Gorky (nowNizhniy Novgorod), USSR. He obtained his PhD inMechanical Engineering from the Delft University ofTechnology. In 1998 he has joined the Section of Road

and Railway Engineering, Faculty of Civil Engineeringof TU Delft. At present, he works as an Assistant Pro-fessor (tenure) at the Section of Railway Engineering.

Guoqing Jing is currently a Full Professor of theHighway and Railway Engineering Department at Bei-jing Jiaotong University, China. He obtained his PhDdegree in Civil Engineering from INSA de Rennes,France. He was invited as a visiting Professor to UIUC,USA, and TUD, Netherland. He has also sided-workedfor several companies in the railway industry. He servedas a Vice Director of the State Key Lab of Waterprooffor China, and Guest Professor for UMP, Malaysia, etc.He is working on a ballasted track, especially recycledand composite materials, and his tools are DEM andFEM.

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An experimental and numerical study on the mechanical