TEST METHODS AND REQUIREMENTS FOR FASTENING SYSTEMS FOR CONCRETE SLEEPERS

Harmonizacija tehničke regulative u oblasti železničke infrastrukture još uvek je u toku u Republici Srbiji. Evropski komitet za standardizaciju (European Committee for Standardization CEN) izradio je seriju standarda EN 13481 – Primene na železnici – Kolosek – Tehnički uslovi za sisteme pričvršćenjа, koja se sastoji iz sledećih osam delova: − Deo 1: Definicije [1]; − Deo 2: Sistemi šinskih pričvršćenja za betonske pragove [2]; − Deo 3: Sistemi šinskih pričvršćenja za drvene pragove [3]; − Deo 4: Sistemi šinskih pričvršćenja za čelične pragove [4]; − Deo 5: Sistemi šinskih pričvršćenja za konstrukciju koloseka bez zastora, sa šinom položenom na gornju površinu ili u kanalu ploče [5]; − Deo 6 (nacrt evropskog standarda): Specijalni sistemi šinskih pričvršćenja za prigušenje vibracija [6]; − Deo 7: Specijalni sistemi šinskih pričvršćenja za skretnice, ukrštaje i šine vođice [7];


INTRODUCTION
Harmonization of technical regulation in the area of railway infrastructure is still in progress in the Republic of Serbia. European Committee for Standardization (CEN) has created a group of standards EN 13481 -Railway applications -Track -Performance requirements f or fastening systems, which consists of eight parts as listed below: − Part 1: Definitions [1], − Part 2: Fastening systems for concrete sleepers [2], − Part 3: Fastening systems for wood sleepers [3], − Part 4: Fastening systems for steel sleepers [4], − Part 5: Fastening systems for slab track with rail on the surface or rail embedded in a channel [5], − Part 6 (European Prestandard): Special fastening systems for attenuation of vibration [6], − Part 7: Special fastening systems for switches and crossings and check rails [7], − Part 8: Fastening systems for track with heavy axle loads [8].
The above mentioned parts 1 -8 are adopted by the Institute for standardization of Serbia (ISS) [9], as shown in Table 1. SRPS EN 13481 Serbian standard series is identical with EN 13481 European Standard series.
In addition, EN 13146 -Railway applications -Track -Test methods for fastening systems supports t he requirements defined in EN 13481 series and consists of the following parts: − Part 1: Determination of longitudinal rail restraint [10], − Part 2: Determination of torsional resistance [11], − Part 3: Determination of attenuation of impact loads [12], − Part 4: Effect of repeated loading [13], − Part 5: Determination of electrical resistance [14], − Part 6: Effect of severe environmental conditions [15], − Part 7: Determination of clamping force [16], − Part 8: In service testing [17], − Part 9: Determination of stiffness [18]. The parts 1 -9 of EN 13146 standard series are adopted by the ISS [19], as shown in Table 2 The adopted SRPS EN 13481 and SRPS EN 13146 standard series are not translated into Serbian language, except the titles and scopes. Significant obstacle to the effective implementation of the adopted SRPS EN standards in engineering practice is the lack of official translation in Serbian language.
Since there was a great interest by the engineering public for the subject, this paper is the wider version of the paper presented at the International conference RAILCON 2016 held in Niš, Serbia on 13th of October, 2016 [20].

TEST METHODS FOR RAIL FASTENING SYSTEMS
Since fastening systems are safety critical, there is a need to have a standardised procedure to evaluate their performance in normal use. It is obvious that the real conditions in track cannot always be simulated in laboratory tests from EN 13146 Parts 1 to 7 [10 -16] and Part 9 [18]. Consequently, performance of rail fastening systems on European railway network is determined by laboratory test methods and in service testing (Part 8 [17]) in accordance with the EN 13146 standard series. These test procedures are applied to a complete fastening assembly. The definitions of the terms used in the EN 13146 series were specified in the EN 13481-1 European Standard [1].
After performing the measurements according to [10 -18], it is necessary to draw up a test reports, which includes information in accordance with the requirements of the relevant part of standard series.

Determination of longitudinal rail restraint
The European Standard EN 13146-1 [10] specifies a laboratory test procedure for determination of maximum axial load that can be applied to a rail, secured to a sleeper, bearer or element of slab track by a rail fastening assembly, without non-elastic displacement of the rail (Figure 1). The specified test procedure applies to a complete fastening assembly taking into account the following: − procedura ispitivanja meri podužni otpor šine za diskretne sisteme pričvršćenja sa šinom fiksiranom za oslonac (prag, dugački prag skretničke građe ili element čvrste kolosečne podloge) u diskretnim intervalima; − procedura ispitivanja meri podužnu krutost za athezivne sisteme pričvršćenja sa "utopljenom" šinom (embedded rail).
− the test procedure measures the longitudinal rail restraint for discrete fastening systems, with rail fixed to a supporting base (sleeper, bearer or element of slab track) at discrete intervals, and − the test procedure measures the longitudinal stiffness for an adhesive fastening system with an embedded rail.

Determination of torsional resistance
EN 13146-2 European Standard [11] specifies a laboratory test procedure to determine torsional resistance of complete fastening assembly, which is measured as the moment necessary to rotate a rail through 1° in a plane parallel to the base of the support ( Figure 2). The obtained value of torsional resistance is used in track stability calculations. Slika 2. Postavka ispitivanja za određivanje otpora zaokretanju šine i primer dijagrama otpora zaokretanju šine Figure 2. Test arrangement for determination of torsional resistance and an example of torsional resistance diagram

Determination of attenuation of impact loads
EN 13146-3 European Standard [12] specifies laboratory test procedures for comparing the strains induced with a low attenuation reference rail pad and with the test pad in the fastening system. An impact load is applied by dropping a mass onto the rail head ( Figure  3). Rail is fastened to a concrete sleeper or bearer.

Determination of effect of repeated loading
EN 13146-4 European Standard [13] specifies a laboratory test procedure for applying repeated loading which simulates the load caused by traffic on railway track ( Figure 4). This test is used for assessing the long term performance of fastening system in which a rail is directly secured to the supporting structure with or without a beseplate ("direct fastening systems" as in [1]). In addition to other necessary information, test report contains result of visual inspection after the test ( Figure  5), mean vertical static stiffness before and after cyclic  loading, longitudinal rail restraint before and after cyclic loading, clamping force before and after cyclic loading, mean dynamic rail displacement at the beginning and the end of the repeated load test, mean residual displacement at maximum load at the end of the repeated load test.

Determination of electrical resistance
EN 13146-5 European Standard [14] specifies a laboratory test procedure for determining electrical resistance in wet conditions. The electrical resistance between two short lengths of rail fastened to the support (steel or concrete sleeper, bearer or element of slab track) is measured whilst the whole support and fastenings are sprayed with water at a controlled rate ( Figure 6). Figure 6. Determining the electrical resistance in wet conditions in laboratory

Effect of severe environmental conditions
EN 13146-6 European Standard [15] specifies a laboratory test procedure for determining the effects of severe environmental conditions on the fastening system ( Figure 7). During the test, the complete fastening assembly is exposed to a salt spray and the effect on ease of dismantling, and reassembly, and condition of individual components is recorded. Test report includes change in appearance of each component during the test and any failure to dismantle or reassemble the fastening system. The future revisions of this standard should include test procedures for covering other environmental conditions. Slika 7. Oprema za ispitivanje pomoću slanog spreja Figure 7. The equipment for the salt spray test

Determination of clamping force
EN 13146-7 European Standard [16] specifies laboratory test procedures for measuring clamping force ("force applied to the upper surface of one rail foot by the fastening assembly clips" as in [1]) acting on the foot of a rail. The clamping force for a complete rail fastening assembly is determined by measuring the force necessary to separate the rail from the surface on which it is supported (Figure 8). The test procedure is applicable to fastening systems with and without baseplates on sleepers, bearers and elements of slab track. Figure 8. Test arrangement for measuring the vertical force necessary to separate the rail from support structure in laboratory

In service testing
EN 13146-8 European Standard [17] provides a procedure which can be used to compare the performance of new or modified fastening systems in track with systems whose performance is known. The fastening system under test is installed in track at the same time and at the same conditions (the same grade and section of rail, sleepers, bearers or slab track of the same material and design, as well as location in track with similar geometry and service conditions) as a reference fastening system. Length of the test section should not be less than 500 sleepers with installed test fastening system and 500 sleepers with installed reference fastening system (200 sleepers each on metro systems), or their equivalent (slab track). Duration of the test corresponds to the traffic dynamics required to pass over the test track (e.g. 20 × 106 gross t in track with maximum axle loads > 100 kN) and shall not be less than one year. During the test each fastening system shall be maintained in accordance with the manufacturer's instructions. Inspection of the test and reference fastening systems includes: − merenje širine koloseka; − podužno pomeranje šine, relativno u odnosu na prag ili čvrstu kolosečnu podlogu i maksimalni raspon dnevne temperature; − uticaj na performanse signalnih sistema; − silu pritezanja (na ne manje od deset sklopova) korišćenjem metode ispitivanja u koloseku, koju preporučuje proizvođač; − sigurnost veze s pragovima; − stanje na glavi šine; − stanje pragova uključujući zonu oslanjanja šine na prag; − stanje pojedinačnih komponenata pričvršćenja; − jednostavno ugrađivanje i demontiranje korišćenjem alata po preporuci proizvođača.
− track gauge measurement, − longitudinal movement of rail, relative to the sleeper or slab support, and maximum daily temperature range, − effect on performance of signalling systems, − clamping force (on not less than 10 assemblies) using the manufacturer's recommended test method for use in track, − security of attachment to the sleepers, − condition of the rail head, − condition of sleepers including rail seat area, − condition of individual fastening components, − ease of assembly and removal using the tools recommended by the manufacturer.

Determination of stiffness
EN 13146-9 European Standard [18] provides together test methods for measuring the stiffness of pads and fastening assemblies under static, low frequency and high frequency dynamic loading. Test arrangement for pads is shown in Figure 9.
Test procedures for complete rail fastening assemblies include static test procedure, dynamic low frequency test and dynamic high frequency test ( Figure  10). Figure 9. Test arrangement for measuring the stiffness of pad Slika 10. Postavka ispitivanja za dinamičku krutost kompletnog sklopa pričvršćenja Figure 10. Dynamic stiffness test arrangement for complete rail fastening assemblies Dobijena vrednost krutosti koristi se u proračunu stabilnosti koloseka.
The obtained value of stiffness is used in track stability calculations.

PERFORMANCE REQUIREMENTS FOR FASTENING SYSTEMS ON CONCRETE SLEEPERS
The definitions of the terms used in EN 13481 European Standard series were specified in EN 13481-1 [1]. In accordance with [1], "fastening system is assembly of components which secures a rail to the supporting structure and retains it in the required position whilst permitting any necessary vertical, lateral and longitudinal movement".
This standard series considers specific requirements for fastening systems depending on the type of supporting structure (concrete sleepers [2], wood sleepers [3], steel sleepers [4], slab track [5]), as well as requirements for special fastening systems (for attenuation of vibration [6], switches and crossings and check rails [7] and for track with heavy axle loads [8]).
Performance requirements for fastening systems for use on concrete sleepers in ballasted track include longitudinal rail restraint, torsional resistance, attenuation of impact loads, effect of repeated loading, electrical resistance of fastening system and sleeper, effect of exposure to severe environmental conditions, overall dimensions, effect of fastening system tolerances on track gauge, clamping force, and in-service testing.
Required longitudinal rail resistance depends on the speed limit and the special requirements of substructure. In that sense, the longitudinal rail resistance shall be not less than 7 kN (controlled over the measurement process according to EN 13146-1) on the conventional rail lines and not less than 9 kN on high-speed lines (≥ 250 km/h).
In accordance with the design of the track supporting structure, the minimum requirement for longitudinal restraint may be reduced by agreement between the purchaser and manufacturer. For example, the utilization of expansion devices to prevent excessive longitudinal displacements and forces on the long railway bridges is expensive and bad solution in regard to traffic safety and comfort, as well as maintenance costs. Therefore, it can be applied an alternative solution of fastening system with reduced rail longitudinal restraint. Figures 12 and 13 show the PANDROL® ZLR (Zero Longitudinal Restraint) system designed to keep track forces from being transmitted to bridge, to hold the rail vertically in place, to provide lateral restraint and to prevent rail rollover.
The torsional resistance is measured in accordance with [2] and the result reported.
For fastening systems described as having medium or high attenuation of dynamic loads, test shall be conducted in accordance with [3] and the result reported. Test results for medium attenuation shall be in the range from 15 % to 30 %, and for high attenuation over 30 %.
The assembly static stiffness and assembly low frequency dynamic stiffness shall be measured in accordance with [19]. At the request of the customer, the rail pad static stiffness, low frequency dynamic stiffness of the rail pad and the assembly high frequency dynamic stiffness should be measured in accordance with [19] and [2] (loads for measurement of stiffness were defined in [2]). Uticaj ponovljenog opterećenja treba da se odredi u skladu s procedurom definisanom u [13], koriščenjem opterećenja za ispitivanje i pozicije koje su definisane u [2]. U skladu sa [13], treba obaviti sledeća merenja pre i posle ponovljenog opterećenja: The effect of repeated loading shall be determined by the procedure defined in [13] using the test loads and positions defined in [2].
In accordance with [13], the following measurements shall be performed before and after repeated loading: − longitudinal rail restraint (permitted change ≤20%), − vertical static stiffness change (permitted change ≤25%), and − clamping force (permitted change for f astening systems which act on the foot of the rail ≤20%).
The electrical insulation shall be not less than 5 kΩ when measured in accordance with [14]. The user may specify a higher value for use with certain track circuits (guidance on traction currents is given in [24] and SRPS EN 50122-2).
Effect of exposure to severe environmental conditions is determined in accordance with [15] based on the salt spray test. After the test, the fastening assembly shall be capable of being dismantled, without failure of any component and reassembled using manual tools provided for this purpose. Figure 14 shows the envelope for rail fastening systems (which act on the foot of the rail) for concrete sleepers in ballasted track and rail section in accordance with [22] (excluding 49E4) and [23]. This envelope is necessary to avoid interference with vehicles including track maintenance vehicles.
It should be noted that for web support fastening systems, the minimum flangeway shall comply with national regulations and the envelope of the fastening systems shall be provided by the supplier. Proizvođač treba da obezbedi tehničke crteže veze sistema pričvršćenja i praga. Promene statičke širine koloseka, koje se mogu pojaviti usled sistema pričvršćenjane treba da pređu ± 1 mm.
The manufacturer shall provide a drawing of the interface between the fastening system and the sleeper. The variation in the static track gauge which can arise from the fastening system shall not exceed ± 1 mm.
Clamping force for fastening systems (acting on the rail foot) shall be determined by the procedure prescribed in [16] and the results shall be reported. The requirement for clamping force is inapplicable to web support fastening systems.
In-service testing shall be carried out in accordance with [17] at the request of the customer.
Other specific requirements for fastening system must be defined by the customer.

CONCLUSION
In this paper, technical requirements for rail fastening systems on rail lines with design axle load up to 350 kN were considered in accordance with EN 13481 European Standard series. It points to the mandatory requirements and according to the European standards and specific requirements according to the conditions of the project.
The paper presents the performance requirements for fastening systems on concrete sleepers in ballasted track since these fastening systems are commonly used in Serbia.
Test methods for fastening systems were particularly discussed in accordance with EN 13146 European Standard series.
Both of the above mentioned standard series were adopted by the Institute for Standardization of Serbia as Serbian standards SRPS EN 13481 (Parts 1 -8) and SRPS EN 13146 (Parts 1 -9). State of the art in the harmonization process of both standard series is shown in Tables 1 and 2. Implementation of SRPS EN standards is difficult because they were published only in English.
The aim of the paper is to introduce engineering public in Serbia with mentioned two standard series and to facilitate their practical implementation.