final report summary

7/30/2019 Final Report Summary

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Analysis of Short and Long-termbehaviour of Ballast and Slab Railway

Track

Ref. PT-2006-024-19CCPM

Final Report: Summary

School of Civil Engineering(Escuela de Ingenieros de Caminos, Canales y Puertos)

Technical University of Madrid(Universidad Politcnica de Madrid)

Investigador Principal: Jos M. Goicolea Ruigmez (Universidad Politcnica de Madrid)Versin: 1Fecha: 1 dic 2009

CENTRO DE ESTUDIOS YEXPERIMENTACIN DE OBRASPBLICAS


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TABLE OF CONTENTS

Executive Summary ............................................................................................. 31 Subproject SP1 (UPM): Mechanical characterisation and study of damageevolution in ballast and slab track systems .......................................................... 42 Subproject SP2 (FCH): Reference parameters, longitudinal interaction lawsand design guide for slab track systems .............................................................. 63 Subproject SP3 (CEIT, UPV): Interaction of vehicles and rolling stock withballast and slab track systems .............................................................................. 74 Subproject SP4 (US): Transmission of vibrations to the ground and nearby

structures through ballast and slab track systems ............................................. 105 Subproject SP5 (CENIT-UPC, UPM): Analysis of Life Cycle Costs for slaband ballast track systems ................................................................................... 12



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Executive Summary

The goal of the project is to study track types in the new high performancerailway lines, mainly in the High Speed Train for passengers, although mixedpassenger-freight traffic may also be considered in some cases. These linescorrespond to TSI category of line I as defined in the new TechnicalSpecifications of Interoperability (TSI) for the Trans-European Network (TEN).The approach of the work is to obtain a comparison of the performance andrequirements of the new track technologies as compared with the traditionalballast track.

The project as a whole comprises 5 distinct sub-projects, each performed by adifferent research centre. The research work developed consists mainly innumerical calculation models and in engineering work, without includingexperiments which would require a much higher budget than was available. Theprincipal researcher for the complete project has been Jos M. Goicolea(UPM). The different sub-projects and the centres responsible for each one are:

SP1: Mechanical characterisation and study of damage evolution inballast and slab track systems. (UPM, general project coordinatingcentre)

SP2: Reference parameters, longitudinal interaction laws and designguide for slab track systems (FCH)

SP3: Interaction of vehicles and rolling stock with ballast and slab tracksystems. (CEIT, UPV)

SP4: Transmission of vibrations to the ground and nearby structuresthrough ballast and slab track systems. (US)

SP5: Analysis of Life Cycle Costs for slab and ballast track systems.(CENIT-UPC, UPM)

The acronyms employed stand for UPM = Universidad Politcnica de Madrid(Escuela de Ingenieros de Caminos), FCH = Fundacin Caminos de Hierro,CEIT = Centro de estudios e investigaciones tcnicas de Guipzcoa, UPV =Universidad del Pas Vasco, US = Universidad de Sevilla, CENIT-UPC = Centrode innovacin del transporte de la Universidad Politcnica de Catalua.

The next sections include, for each of the sub-projects, a summary ofobjectives, methods, results and final conclusions.



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1 Subproject SP1 (UPM): Mechanical characterisationand study of damage evolution in ballast and slab tracksystems

As a first step (task 1.1) a consensus classification of slab rail systems hasbeen performed, selecting the types of track to consider in the differentsubprojects under the various approaches:

Ballast track of similar characteristics to that of the line Madrid-Zaragoza-Barcelona.

Slab track Rheda 2000, with one elastic layer and continuous reinforcedconcrete slab.

Slab track AFTRAV, with one elastic layer and discontinuous prestressedconcrete slabs.

Slab track Stedef, with two elastic layers (in railpads and undercassoulets)

In task 1.2 numerical Finite Element Models (FEM) in the time domain havebeen developed to evaluate the dynamic actions on the track. Three types ofresults have been obtained:

Time history of the rail-wheel contact force. Time history of force transmitted through the primary suspension to the

bogie. Time histories of the forces transmitted by the railpads to the sleepers or

the slab of the track structure, in 14 supports previously selected.

Table 1.1: Summary of dynamic amplification factors for distributed irregularities

Type of track Rail-wheelcontact

Railpads Primary bogiesuspension

Ballast 1,33 1,25 1,1

Rheda 2000 1,32 1,24 1,1

AFTRAV 1,32 1,29 1,1

Stedef 1,37 1,33 1,1

Following the main conclusions are summarised for the results of dynamicactions on the track:

The main dynamic effect is produced by rail irregularities and interactionwith the dynamics of the railway vehicle. The dynamic increment of theaxle loads transmitted by the railpads to the sleepers or the slab, due tothe distributed irregularities under the intervention limit, is moderate andof similar order in all cases, between 25% and 33%.

The increment of dynamic load at the wheel-rail interface for this samecases is also moderate and lies between 32% and 37%.

As relates to the vehicle, significant interaction between different axles is

not observed, not even between the axles in the same bogie. As a



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consequence, the models considered represent axle, or equivalently bogie or 1/8 vehicle. The increment in dynamic load transmitted to thevehicles through the primary suspension is small, in all cases consideredunder 10%.

The objective of task 1.3 has been to evaluate the settlements produced in theembankments and suggest some limits and requirements depending on thetype of slab track. The focus has been on short and long-term settlements dueto rheological actions, water etc. The work consists in the development ofseveral analysis models for total and differential displacements in embankmentsof different heights and qualities. Typical results from one of the Finite ElementModels for settlement calculation are shown in figure 1.1.

Figure 1.1 Finite Element Model for one case of embankment and contour mapof settlements.

From the results obtained, in order for the settlement at the top of theembankment to be lower than 25-30 mm after 10 years, embankment heightmust not exceed 7-10 m assuming the material and compacting conditionsprovide an average deformation modulus of the order of 40 MPa, which may be10-13 m when the deformation modulus is close to 60 MPa. If the Moduluswould be around 80 MPa, the embankment could reach up to 14 m height in

order for the settlement at the top not to exceed the indicated limits.The work carried out in task 1.4 has been a study of the damage evolution inthe long term of two slab track systems: a system with pre-stressed precastslabs and a system of reinforced concrete continuous slab performed in-situ.The study focuses on the influence of the following effects in the long term forstructural behaviour: differential settlement between the slab track and thefoundation; fatigue from the repeated action of the traffic load train; crackingfrom the acting forces and shrinkage of concrete; loss of functionality of thestructure due to high deformations.



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In the case of the prefabricated pre-stressed track, safety against fatigue isguaranteed even in the worst case of differential settlements consideredbetween the slab and the foundation (5.0 mm in 5.10 m). As a result, the pre-stressing must be designed according to the requirements of ultimate limitstates. The criterion of acceptance of differential settlements is, as aconsequence, that of loss of functionality of the track from too high verticaldisplacements.

The analyses performed in the reinforced concrete slab track indicate that thebehaviour for fatigue is also good, provided weldings between rebars areavoided. The problems arise first from loss of functionality due to fatigue ratherthan fatigue in the rebars. Values above the acceptable limits for deformationsand crack widths are obtained when there is a differential settlement betweenslab and embankment of length exceeding 10 m.

2 Subproject SP2 (FCH): Reference parameters,longitudinal interaction laws and design guide for slabtrack systems

From the results of analyses performed for longitudinal interaction between railand platform, it is concluded that the only case in which the presence of slabtrack may influence significantly the design due to track-structure longitudinalinteraction is that of short continuous viaducts.

The existence of slab track with normal rail supports in the case of continuousrail represents an important factor in the design of the viaduct, as it requires toreduce considerably the maximum dilatation lengths (which decrease frombetween 110 and 115 m for ballast track to between 65 and 70 m for slab track).In this context it may be expected that the slab track infrastructure will cause amodification of the criteria for selection of structural types, which will tend to agreater presence of isostatic deck solutions. Alternatively a more frequentintroduction of track dilatation devices will be needed on the abutments of thestructures.

Apart from some technical considerations, both alternatives may be evaluatedfrom an economic point of view, and be integrated in the study of life cycle costof the infrastructure as a whole, in order to establish a complete comparison ofboth track alternatives.

However, as has been seen, this design limitation may be avoided byintroducing special sliding supports with a maximum longitudinal resistancelimited to around 23 kN/m of track. In this case the maximum lengths ofdilatation for the case of slab track are near thos of ballast track, reachingvalues of around 100 m. In that case the technical and economic considerationsto take into account refer to the technical suitability and the cost ofimplementing such special supports. For this it will be necessary to resort to the

experience of the railway companies that have adopted this solution in their



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viaducts with slab track, as is the case of Germany (with the special sliding clipsSKL 13, the yellow clips). Currently there are studies under way, through themeasures of stresses in the rail in viaducts with slab track and special fixations,to evaluate the efficiency of the introduction of such fixations.

As relates to the Service Limit State, from the analyses performed a veryrevealing conclusion is extracted, the fact that these limitations do not representin general a design criterion that introduces differences in the dimensioning ofthe bridge decks as a function of the selected track type. However, this choiceleaves open a possibility that in the case of employing fixations with verydifferent vertical stiffness or pre-stressing torque to those considered, thecorresponding limit values could eventually be more restrictive.

In task 2.4 the most relevant conclusions of the subproject are summarised, aswell as the main conclusions of the rest of subprojects, with the objective ofestablishing the recommendations derived for the evaluation and design of aslab track system. Among the most relevant conclusions the following arehighlighted:

- those related to the geotechnical aspects of the platform and thedamage evolution for slab track, for elaboration of recommendationsfor the construction of embankments and earth structures for slabtrack.

- Those related to longitudinal interaction between track and structureand the analysis of limitations of Service Limit States in structures, forelaboration of recommendations relative to the design of viaducts for

slab track.- Those related to vibration control, for the elaboration ofrecommendations relative to vibration control measures for slab track.

3 Subproject SP3 (CEIT, UPV): Interaction of vehiclesand rolling stock with ballast and slab track systems

The overall objective of this subproject has been the analysis of interactionbetween rolling stock (axles, bogies, vehicles) with the track, consideringspecially the possible differences between the various track systemsconsidered. For this purpose aspects considered comprise from low frequency

dynamic phenomena associated to the movements of the body to the highfrequency effects related to rail corrugation.

In task 3.1 (CEIT) both the vehicle and the track are modelled within themultibody analysis program for dynamics of mechanisms SIMPACK. Thevehicle considered for the study is a high speed one based on the ICE-3, whoseparameters are detailed in the annual project report for 2007. The connectionbetween wheel and rail is considered through a special element fromSIMPACK's railway module which solves the contact problem following thetheories of Hertz and Kalker.



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(a) (b)

Figure 3.1. Model for track in SIMPACK with rigid body elements: (a) without

longitudinal connection between bodies; (b) with longitudinal connectionbetween slab bodies.

The following conclusions have been obtained from the work in this task: With the models developed, the ballast reference track presents better

results from the point of view of transmitted forces than either of the twoslab track systems studied.

Modelling in SIMPACK of slab track systems RHEDA 2000 and STEDEFexclusively with rigid body elements presents some limitations. Thetechnique employed in SIMPACK for modelling the slab requires theintroduction of a body under each axle, and hence the movement of each of

these bodies is independent from the rest. This however does notcorrespond with reality as the slab is continuous. It is possible to restrain the motion of these bodies so that all of them share

the same movement, or to establish links with elastic elements and viscousdampers. However, the real movement of the slab will not be reflected byneither of the above models, as the slab is a rigid body with its own dynamicdegrees of freedom.

If within the multibody models for the track the elastic layer under the slab iseliminated, the effect on the model is as if the slab did not exist. In this casethe filtering effect produced by the slab mass would be lost.

Additionally (task 3.1, UPV) the different types of slab and ballast track havebeen compared from the point of view of inscription of the vehicle in curvedtrack. Its concluded that the risk of derailment according to parameter Y/Q isclearly below 0,8 for all axles, with all track radii and all track types considered.For the track with the smallest radius, the RHEDA track appears to yield aslightly largerY/Q value.

In task 3.2 the track has been considered as a continuous and deformablesystem. For this the track has been modelled with finite elements. In SIMPACKit is possible to include the flexibility of some bodies, performing first a modalanalysis through a finite element analysis program. The results from this



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analysis are exported to SIMPACK through an interface that links bothprograms. The response (receptance) of the track is shown in figure 3.2 andtable 3.2.

Receptancia en el centro del vano central

0,00E+00

1,00E-08

2,00E-08

3,00E-08

4,00E-08

5,00E-08

6,00E-08

7,00E-08

8,00E-08

0 200 400 600 800 1000 1200 1400 1600

[Hz]

[m/N]

BALASTO

RHEDA 2000

STEDEF

AFTRAV

Figure 3.2. Receptance showing the response at the centre of the track.

Table 3.1. Frequency in Hz of the most relevant modes of vibration for the tracktypes considered

Ballast STEDEF RHEDA AFTRAV

Mode 1 78 69

Mode 2 288 375 120 158

Mode 3 1070 1070 940 938

From a general point of view, the main conclusions obtained in task 3.2 are thefollowing:

The models that combine multibody rigid elements with finite elementsprovide reliable results in the range of low and middle frequencies.

In the range of high frequencies, the auxiliary stiffness Kaux that isemployed for transmitting the wheel-rail contact forces to the flexibleelements influences the results.

If the models are to include a large number of modes for the track, thecomputational cost increases very much, due to the large number ofdegrees of freedom of the model. If it is desired to study high frequencyphenomena, it is proposed to work with 2D simplified models withmasses, springs and dampers, considering only the vertical movement,as the 3D models described before are not necessary.



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In task 3.3 (UPV) the rail corrugation has been studied, for the four track types(ballast, STEDEF, AFTRAV and RHEDA 2000). For this the program RACINGhas been employed for computing the receptance functions and the functions ofrail corrugation growth in all track types, and NASTRAN for computing thereceptance functions of AFTRAV rail type.

It may be concluded that for normal track radii, the possibility of producingcorrugation is low. It has been observed, for all cases studied, and all track radiiand train velocities, that RHEDA 2000 track is the one with fewer possibilities tosuffer corrugation phenomena, followed by the ballast track and AFTRAV.

4 Subproject SP4 (US): Transmission of vibrations tothe ground and nearby structures through ballast andslab track systems

The main objectives of subproject SP4 have been: Develop and apply an innovative computational methodology for studying

the vibrations transmitted through the ground originated by railway traffic Study and compare the vibrations transmitted by the different track

systems considered in the project. Study possible measures for mitigating the vibrations transmitted by the

ground to nearby structures or facilities

For this purpose the following tasks have been performed:

Task 4.1: basic definition of models and selection of parameters and datafor models. Task 4.2: Obtain calculation results and perform critical analysis. Task 4.3: Study of anti-vibration measures and development of

conclusions.

These tasks have been developed employing three type of dynamic models,two in the frequency domain and one in the time domain: Semi-analytic model in the domain of frequency and wave lengths. Numerical periodic model in the frequency domain based on the boundary

element method. Three-dimensional numerical model in the time domain coupling the finiteelement method and the boundary element method.

The numerical models enable modelling the track, the nearby structures, over orunderpasses etc. for the study of dynamic soil-structure interaction. The modelin the time domain can take into account the excitation mechanisms generatedby the railway traffic: passage of an axle at a certain velocity, irregularities ofwheels and rail and discrete effect of sleepers.

The general technical conclusions from the study show the influence of variousparameters in the level of vibrations transmitted through the ground or in nearby



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structures and originated by the passage of trains, distinguishing between bal-last and slab track. The parameters studied are the following:

Distance from the structure or observation point to the track. The velocity of the train. The existence of one, two or three levels of damping. The properties and stratification of the ground.

The vibrations caused by trains circulating over slab track and ballast track dif-fer in the following aspects: The levels of vibration obtained in the rail are higher for the ballast track. In

the case of of slab track, the excitation is distributed in a near uniform way inthe complete frequency range. In both track types, the stratification of theterrain will determine if amplifications are obtained for certain excitation fre-quencies.

The critical train velocity for which the vibrations are amplified is determinedby the properties of the track and specially those of the ground. This criticalvelocity is approximately equal to the speed of propagation of Rayleighwaves in the ground, although due to system characteristics, it is higher withslab track than with ballast track.

The level of vibrations is higher as the train speed is increased, until the crit-ical train velocity is achieved. After this critical velocity vibrations decreaseeven if the train speed increases.

In the track, the excitation mechanism originated by the passage of a singlemoving axle governs the response. As the observation point is further awayfrom the track, the excitation mechanisms originated by the wheel and rail ir-

regularities govern the vibration response. As a consequence, the modellingof wheel and track irregularities is very important in order to predict the vi-brations near the track.

The inclusion of one level of damping under the slab may contribute to atten-uate the vibrations produced by the passage of trains. This system must bedesigned so that the isolation frequency be as low as possible, in the rangeof 10-15 Hz. If not, the influence of this new damping level would not be no-ticeable.

In order to predict the vibrations originated by passage of trains, it is import-ant to model precisely the section of the slab track and of the ballast track. Ifboth types of track are modelled accurately, the level of vibration obtained inboth track types is similar for the same soil and rolling stock.

The different types of slab track studied produce similar vibration levels, spe-cially if a layer is included of some 30 cm of poor concrete and with an ad-equate sub-base. The track type Stedef produces slightly higher vibrationlevels. This result also indicates that models which do not include the layerof poor concrete and granular sub-base may not reflect adequately the be-haviour of the track as regards the vibrations produced.

The vibrations obtained in a building nearby to the track has been analysed,considering the vibration levels according to the regulation in thirds ofoctave. This analysis, obviously, has been carried out for a particular build-

ing and its dynamic characteristics will determine if the response is amplified



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or not, but nevertheless general conclusions may be extracted for the effectof track types. The influence of distance is very important, being observed a medium

level of decrease in the computed accelerations. The influence of train velocity is significant from above 5 Hz approxim-

ately. Below this frequency level the accelerations registered in the mod-el are similar, independently of velocity, and after the said level thecurves separate significantly. Acceleration is appreciably higher as thetrain velocity increases.

The excitation caused by wheel and rail irregularities determine the re-sponse.

With regard to the damping levels, the importance of the design of anelastomeric blanket under the track has been confirmed again.

5 Subproject SP5 (CENIT-UPC, UPM): Analysis of LifeCycle Costs for slab and ballast track systems

Subproject SP5 has been structured in the following four tasks: 5.1- analysis ofinvestment costs for the different track systems; 5.2- evolution of themaintenance costs for the different track systems; 5.3- Development of a modelfor analysis of life cycle costs (LCC); and 5.4- application of the LCC model:evaluation of the different systems.

The tasks 5.1 and 5.2 were carried out by CENIT-UPC. However, this centreabandoned the project at the beginning of 2008, due to this fact it was not

possible for them to complete the remaining work in tasks 5.3 and 5.4 asforeseen. These tasks were retaken, with the agreement by CEDEX, by aresearch group in the Escuela de Ingenieros de Caminos at UPM.

Due to their technical characteristics, the structures of slab track and ballasttrack experience different life times, as well as a non-constant distribution ofcosts with time (being generally greater the construction costs and lower thoseof maintenance and renewal in the case of slab track).

Following the main remarks and conclusions are presented in summary withrelation to the development and application of the LCC model:

The model developed does not yield results which may be consideredprecise and unquestionable, rather it provides a support tool for decisionmaking which shows more favourable tendencies as a function of rangesof parameters of the line, distinguishing between the two types of railwayinfrastructure considered.

In spite of the previous remark, the model does provide the current netvalue (CNV) of the life cycle costs of the two systems being comparedand allows en economic evaluation of the suitability of one system oranother, in selected cost scenarios.

From the starting point of the effects of variations in parameters it hasbeen possible to establish two scenarios for each track system, one



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under the most favourable conditions for the system for which the currentnet value is calculated and another with the most favourable conditionsfor the other system.

Scenario 1: Current net value of the slab track system with themost unfavourable conditions for the slab track system (VP Esc 1).

Scenario 2: Current net value of the slab track system with themost favourable conditions for the slab track system (VP Esc 2)

Scenario 3: Current net value of the ballast track system with themost favourable conditions for the ballast track system (VB Esc 1)

Scenario 4: Current net value of the ballast track system with themost unfavourable conditions for the ballast track system (VB Esc2)

The intersection of the above scenarios generates a rhombus ofdecision, presented in figure 5.1, which represents the cost per kilometre

of track. Each intersection of the current net value (CNV) of the variousscenarios allows us to formulate a working hypothesis in the anaysis ofsuitability of one system over another.

Thus only in the extreme lower and upper areas of the rhombus (markedin dark grey in the figure) we are able to indicate clearly the suitability ofone system over another. The intermediate corners (those situatedbetween the extremes) require us, comparing the favourable-unfavourable scenarios, to expand the study of the type of infrastructureto employ in the line under study.

Figure 5.1 Rhombus of decision of the model of LCC


BalastoPlacaDudoso Mayor prob.

placaMayor prob.balasto


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