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Dynamic behaviour of high-speed rail fastenings in the presence of desert sand
Construction and Building Materials 117 (2016) 220–228
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Dynamic behaviour of high-speed rail fastenings in the presence of desert sand I.A. Carrascal ⇑, J.A. Casado, S. Diego, J.A. Polanco LADICIM (Laboratory of Materials Science and Engineering), University of Cantabria, E.T.S. de Ingenieros de Caminos, Canales y Puertos, Av/Los Castros 44, 39005 Santander, Spain
h i g h l i g h t s Fastening system characterisation for railway under extreme conditions (sandstorms). The tested fastening system is not designed to work in the presence of sand. A slight change in the rail pad design could improve its dynamic behaviour in sand. The presence of sand modifies the mechanical properties of the fastening system. The sand does not affect the mechanical properties of individual system components.
a r t i c l e
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Article history: Received 28 October 2015 Received in revised form 2 May 2016 Accepted 5 May 2016 Available online 12 May 2016 Keywords: Sand Fastening Fatigue Wear Rail pad Railway High speed
a b s t r a c t High-speed lines in Saudi Arabia are subjected to sandstorms. These environmental conditions are not established at laboratory level. This work studies the influence of the presence of sand on the dynamic behaviour of the fastening system. So the evolution of the system is analysed under simulated sandstorm conditions and it is compared with the standard one. Results indicate that the presence of sand in the fastening system generates wear on the sleeper and increases the stiffness after the fatigue test. However, this fact does not modify both the mechanical behaviour and the durability of the individual elements. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction Saudi Arabia has set itself the challenge of designing and building a high-speed railway line, with a UIC gauge double electrified track layout, for speeds of 320 km/h. The line runs between the cities of Medinah and Makkah-Harum (Mecca), covering 444 km in the west of the Arabian Peninsula, and the journey will take less than 3 h [1,2]. The main technical challenge for this engineering work is the highly adverse climatic and geological conditions, the line passes through stretches of dunes, sand and strong winds Abbreviations: FSi, load applied in the static stiffness test; dS, displacement measured in the static stiffness test; kS, vertical static stiffness; FLFPi, load applied in the dynamic stiffness test; dLFP, displacement measured in the dynamic stiffness test; kLFP (i), dynamic stiffness at a frequency of i Hz; dvp, the vertical rail basement displacement; dhc, the horizontal rail head displacement. ⇑ Corresponding author. E-mail address: [email protected] (I.A. Carrascal). http://dx.doi.org/10.1016/j.conbuildmat.2016.05.023 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.
which may cause the occurrence of sandstorms, as well as some sharp temperature changes between day and night. The presence of sand will affect many of the components of the track superstructure, whether ballasted or ballastless track [3,4]. In recent years, the effect of the presence of sand on the rail has been analysed, either on the wheel-rail contact wear [5–10]. The pull-out force goes up significantly, due to, the increase in friction when the injected binder has the addition of quartz sand [11]. The influence of flowing sand grains among the ballast aggregates increases the stiffness of ballast layer, consequently, rail support modulus increases, so the received share of total axle load subsequently, increases on the sleeper which is placed under the wheel load [12,13]. At present there is great concern over the maintenance of the track in the presence of sand and in this respect, a great deal of research has been undertaken on how to prevent the action of the sand by keeping it away from the track [14–21].
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The aim of this work is to verify the influence that the presence of sand may have on the dynamic behaviour of the rail fastening system. For this purpose, a well-known and tested system has been selected, which is the one which is being used in Spain in the newest stretches of the AVE (Spanish high-speed train). The study analyses the evolution of the fastening behaviour, once the system has been subjected to a fatigue test, that reproduces the inclined loads expected when the trains circulates on the track. A comparison will be made between the laboratory situation, which will be the model fastening, and another situation with the presence of sand, in an attempt to simulate in the laboratory a pseudo-sandstorm on the fastening system while it is subjected to the fatigue test. Another objective of the work is the development of the dynamic test in the presence of sand, for which it will be necessary to design a system for conducting and projecting the sand on the fastening system tested. 2. Material For the test set-up, a monoblock prestressed concrete sleeper, ADIF AI-04-AD [22], was selected, equipped with a removable non-rotating insert. The behaviour of the model fastening on one of the sleeper supports was observed, tested under normal laboratory conditions and then, on the other support, an equivalent fastening system was tested but in the presence of sand. The two fastening sets have been considered to be within the D category defined by Standard EN 13481-2 [23]. These fastening sets were intended for lines with curves of a large radius, often used for high-speed trains, and with a typical axle load of 180 kN, a typical curvature radius of 800 m, a rail coupon 60E1, a typical space between sleepers or supports of 600 mm and any typical maximum speed. The fastening system selected for the tests is a modification of the one used in the Madrid-Barcelona AVE which is fitted with the VM fastening system [24]. The modification consists of the replacement of the VAPE dowel-screw system with a removable anti-rotation dowel with an AV-1 lag screw [25]. Therefore, the components of the fastening system are (see Fig. 1):
Sleeper: ADIF AI-04-EA (prestressed concrete monoblock) [22,26]. Flanged plate: A2 (Polyamide 66 + 35 GF) [27]. Rail pad: PAE-2 (Thermoplastic Elastomer, TPE) [28–30]. Insert: removable anti-rotation AV-1 (PA 6.6 + 35 GF) [25]. Screw: AV-1 [25]. Clip: SKL-1 [31].
The other basic element in the present work is sand, the material which must interact with the fastening system while it is in operation. The sand selected should be as similar as possible in size and composition to that found in the desert of Arabia [32–36]. A mixture was made of equal parts of silica sand and sand taken from the Sardinero beach in Santander, with fractions in the range of 0.04–0.4 mm. Table 1 shows the granulometry of the sand.
3. Test methodology In order to analyse the influence of the presence of sand on the dynamic behaviour of the fastening system, the variation in a
Table 1 Granulometry of the sand. Sieve size [mm]
Passing [%]
0.5
0.4
0.25
0.125
0.063
99.9
99.6
28.9
4.3
1.32
series of parameters was evaluated, measured before and after performing a fatigue test on two identical sets, equipped with the same components, but with one under normal laboratory conditions and the other under extreme conditions with presence of sand. In addition to the evolution of the test itself, another way of assessing the damage caused by the fatigue test on the system is to analyse the individual behaviour and the joint behaviour of the various constituents that make up the fastening system. In this case, the stiffness of the rail pad was evaluated both separately and as a whole. For the evaluation of the rigidities, static and dynamic vertical tests were performed on the rail pad and the fastening set according to standard EN 13416-9 [37], as can be seen in Fig. 2a,b. In order to carry out the vertical static stiffness test on the plate and the set, a series of 3 compression load and unload cycles was applied at a speed of 120 kN/min from a minimum value, FS1 = 18 kN, to a maximum of FSmax = 85 kN [23]. The vertical rail displacement (d) was recorded for the 3 cycles as the average of four LVDT transducers placed at each corner of the plate, and the vertical static stiffness (kS) was measured in the load branch during the third cycle according to expression (1) between the strength values FS1 = 18 kN and FS2 = 0,8FSmáx = 68 kN. The test set-up was the same as that of the above test:
kS ¼
F S2 F S1 dS
ð1Þ
dS being the difference of the displacement between the load values FS1 and FS2. In order to carry out the vertical dynamic stiffness tests, with the same set-up as in the static test, 1000 sinusoidal wave cycles were applied between the values of FLFP1 = 18 kN and FLFPmax = 85 kN [23] at the frequencies of 5, 10 and 20 Hz. With the average obtained in the last 10 cycles, the dynamic stiffness (kLFP) was determined according to expression (2)
kLFP ð5=10=15 HzÞ ¼
F LFPmax F LFP1 dLFP
ð2Þ
dLFP being the difference between the displacement between the load values FLFP1 and FLFPmax. The fatigue tests were performed according to standard UNE-EN 13416-4 [38], applying 3 million sinusoidal cycles at a frequency of
Fig. 1. Fastening system tested.
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Fig. 2. Test set-up. Stiffness tests: (a) on rail pad and (b) on fastening set. (c) Cyclic load test.
5 Hz under inclined load between the values of 5 and 70 kN (see Fig. 2c). By means of 6 LVDT transducers, the vertical rail basement displacement, dvp, and the horizontal rail head displacement, dhc, was measured. The inclination angle of the actuator was set at 26°. The fatigue test was carried out on one of the sleeper heads in laboratory conditions, but on the other some extreme conditions were designed with the presence of both sand and of a cloud of the finest fraction of sand caused by a continuous recirculation, an effect which is similar to the environmental conditions to which the fastening set may be subjected in a desert. In the fatigue test with presence of sand, the recirculation of the sand is achieved by using compressed air at a pressure of 8 bars obtaining, by means of the Venturi effect, an aspiration of sand and its subsequent propulsion onto the fastening set (see Fig. 3). As can be observed, a hopper is placed under the sleeper which collects the sand projected onto the fastening set and refeeding the compressed air circuit to send it back to the system. This sand-propelling system was connected an average of 10 h a day.
After completing the fatigue test, the stiffness tests were repeated both on the set and on the plate. The system was not cleaned after the fatigue test to undertake the system stiffness test and it was only cleaned when the system was dismantled in order to perform the tests on the rail pad. Due to the suspicion that the sand could damage any other part of the fastening system, two more tests were planned to carry out in order to verify its effect on the flanged plates and on the corrosion protection of metal components. The lower surface of the flanged plate can erode the concrete of the sleeper, and this effect increases with the presence of the sand during a dynamic test. Static tests up to failure on the outer flanged plates of the two tests, with and without sand, were performed to analyse whether the possible erosion of the nerves in the lower surface affects their mechanical behaviour. The results of these tests were compared with those obtained with the original flanged plates injected into the same mold cavity.
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Fig. 3. Cyclic load test set-up for the configuration with sand recirculation set-up.
The tests were performed in a vertical device that simulates the geometries of the sleeper and the UIC 60 rail foot. Each flanged plate was placed on the sleeper simulator with the corresponding screw, nut and clip, applying a torque of 120 Nm. Then the loading process was executed at a rate of 1 kN/s until the breakage of the flanged plate was obtained. Fig. 4 shows the testing device mounted on a servohydraulic testing machine with 250 kN of capacity. Finally, a corrosion test in a saline mist chamber where a salt water (5% NaCl) solution is atomised at 35 °C by means of spray nozzles using pressurised air during 175 h [39,40] was prepared, considering that the sand might erode the protective layer of the metal components of the fastening system. The metallic elements exposed to saline mist were screws and clips obtained from the two tested fasteners and the same components, not tested previously, in order to compare results. In summary, Table 2 shows the planning of the tests performed in the study, and the sequence in which they were executed. All the tests were performed both at laboratory conditions and under the presence of sand.
Table 2 Testing plan. Components
Test
Pad
1. Vertical static stiffness test 2. Vertical dynamic stiffness test (5/10/20 Hz)
Assembly
3. Vertical static stiffness test 4. Fatigue tests under inclined load (3106 cycles) 5. Vertical static stiffness test
Pad
6. Vertical static stiffness test 7. Vertical dynamic stiffness test (5/10/20 Hz)
Flanged plate Clip and screw
8. Static compression test 9. Corrosion test in a saline mist chamber
4. Results and analysis 4.1. Fatigue tests under inclined load All displacements were recorded throughout the fatigue test, both the horizontal displacement of the rail head and the vertical
Fig. 4. Device for the mechanical characterisation of the flanged plate A2.
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displacement of the rail foot. The graph in Figs. 5 and 6 show the evolution of both parameters over the 3 million cycles for both the model system and the system tested with sand. As can be observed, there is a clear increase in the horizontal displacement of the rail in the system tested with sand, or, in other words, an increase in the line gauge, while there is little change in the vertical displacement, this being slightly higher for the system tested without sand. If, however, stiffness results are analysed, it can be seen that the horizontal stiffness hardly vary at all for the configurations with and without sand, whereas it is the vertical stiffness (see Fig. 7) which shows a significant difference between the two configurations, the stiffness of the system with sand being around 20% higher. The results of the fatigue test are evaluated in terms of the remaining displacements induced between the first test cycles and the last ones after 3106 cycles. Figs. 8 and 9 show the comparison between the first and last cycles for both the horizontal displacement of the head and the vertical displacement of the foot for the two systems tested, with and without sand. Table 3 shows the values of the remaining displacements between the first and last cycles under the maximum and the minimum loading cycles. As can be observed, the vertical displacements are of a very small absolute value, showing hardly any differences between
Fig. 7. Evolution of vertical dynamic stiffness during fatigue test.
hc
Rail head displacement, δ [mm]
1,5
δ
1
δ δ δ
(without sand)
hc,min hc,max hc,min
(without sand)
(with sand)
hc,max
(with sand)
0,5
Fig. 8. Remaining horizontal displacements of the rail head.
0 0
5 10 5
1 10 6
1,5 106
2 10 6
2,5 106
3 10 6
Cycle Fig. 5. Horizontal rail head displacements during fatigue test, dhc.
Fig. 9. Remaining vertical displacements of the rail foot.
Fig. 6. Vertical rail foot displacements during fatigue test, dvp.
the tests with and without sand. Meanwhile, the horizontal displacements of the rail head are of a certain magnitude, being moreover significantly higher in the case of the test sand, 136% for the maximum strength and 40% for the minimum strength.
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Despite the increase in displacement recorded by the rail head in the set-up with sand, the measured values remain within the range of validity, which, according to the technical specification files, is 1 mm. 4.2. Stiffness vertical test on rail pad The rail pads, prior to being mounted, were characterised independently of the fastening system by means of a static and dynamic test at different frequencies. The graph in Fig. 10 shows the evolution of the third of the load cycles applied in the static stiffness test, the cycle in which the measurement of the static stiffness of the plate was made, both for the test prior to the fatigue test and for the subsequent one for the two fastening systems, the model one and the one with sand. It can be seen from the figure that the influence of the presence of sand on the rail pad has been minimal as regards its static behaviour, remaining at all times below a 25% increase, which is the threshold established by the standard currently in use. If the dynamic behaviour is analysed, the results are similar to those obtained in the static test, that is, there are hardly any variations between the initial tests and the tests after the fatigue, as can be observed in the graph in Fig. 11. Table 4 shows in brief the stiffness values obtained for the rail pads before and after the dynamic test for the two set-ups tested. It can be observed that in all cases, there is a slight softening after the dynamic test. 4.3. Stiffness vertical test on the whole fastening system
Fig. 11. Dynamic behaviour of the rail pad.
Table 4 Stiffness of the rail pads tested. Test
Static Dynamic Dynamic Dynamic Dynamic
Stiffness [kN/mm]
(5 Hz) (10 Hz) (20 Hz) (average)
Before dynamic
Without sand after dynamic
With sand after dynamic
133.7 159.2 162.3 183.8 168.7
129.9 151.0 158.7 176.7 162.1
133.3 154.8 162.3 180.5 165.9
(2.8%) (5.2%) (2.2%) (3.9%) (3.9%)
(0.3%) (2.8%) (0.0%) (1.8%) (1.7%)
A static vertical test was performed on the behaviour of all of the system without changing anything, except for a surface cleaning of the sand that had been left on the fastening system. The graph in Fig. 12 shows the evolution of the third of the load cycles applied in the stiffness test, the cycle in which the measurement of the static stiffness is made on the whole system, both for the test prior to the fatigue and for the subsequent one for the two test set-ups used.
Table 3 Remaining displacements.
DFmax DFmin
Without sand [mm]
With sand [mm]
dhc
dvp
dhc
dvp
0.19 0.36
0.02 0.06
0.45 0.50
0.02 0.03 Fig. 12. Static behaviour of the system.
Table 5 Static stiffness of the fastening system. Stiffness [kN/mm] Without sand
Fig. 10. Static behaviour of the rail pad.
With sand
Before dynamic
After dynamic
Before dynamic
After dynamic
158.2
170.1 (7.5%)
170.3
246.3 (44.6%)
Table 5 shows in brief the stiffness values obtained for the fastening set before and after the dynamic bending load test for the two set-ups tested. In this case, it is verified that in both cases, after the dynamic test, the set stiffness, increasing by up to 44.6% in the case of the test with sand, thus exceeding 25%, the limit established for a correct behaviour of the system.
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The justification for this sharp increase in stiffness could be found on dismantling the fastening system. It could be verified that although the sand widely penetrated between the ribs under the flanged plate (Fig. 13), it could not do this under the rail pad except in one of the corners and in the side edges in contact with the flanged plate, Fig. 13a. In contrast, the photograph of Fig. 13b
Fig. 13. Aspect of the fastener once the fatigue test with sand is finished. (a) Under rail pad, (b) upper face of the rail pad.
shows how the sand settled widely in the gaps between the oblongs of the upper face of the rail pad, in contact with the rail plate. The cause for which the sand is introduced in the relief of the upper face and not of the bottom face of the rail pad lies in its own geometry. If the scheme of the rail pad [41] (Fig. 14) is analysed it is found that in the lower face, in contact with the concrete of the sleeper, there is a peripheral nerve that closes the contour of the rail pad and keeps out the sand except for a small amount that is introduced due to the displacement caused by the fatigue test. By contrast, in the upper face, which is in contact with the rail foot, the peripheral nerve does not exist and the sand is able to penetrate. The rail pad is designed so that the channels can function as drainage and, even, as a cooling system for the pad under the action of repeated loads that could generate heat and change its mechanical properties. However, rail pads are not designed to work in the presence of particulate matter, as may be the case in a desert. This is the fact that justifies the increase in stiffness after the dynamic test since the sand that occupies the gaps prevents the correct strain of the plate under loading. Finally, it can be observed in Fig. 15 that, after the dynamic test with sand, the sleeper suffers from wear in the zones that coincide
Fig. 15. Wear produced on the sleeper in the fatigue test with sand.
Fig. 14. Detail of the open areas in the rail pad [41].
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with the nerves of the flanged plate and the outer edge of the rail pad. The depth of the grooves generated on the concrete reaches values of up to 0.4 mm. Similarly, the outer flanged plate tested in sand also had some slight wear, visible with the naked eye, on the surface of the nerve in contact with the sleeper. This wear pushes down the flanged plate and thus lowers the point of support of the clip loop, leading to a loss in clamping force which may be the cause of the increase in the horizontal displacement of the rail head during the fatigue test. 4.4. Static compression test on the flanged plate A2 As mentioned above, the outer flanged plate tested with sand showed appreciable wear that only affected the surface roughness,
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but in no case has the resistant section of the nerves of the plate changed. Fig. 16 shows that three million cycles do not imply any change in the mechanical behaviour of the two plates tested with and without sand with respect to the original plates. 4.5. Test of severe environmental conditions on metallic components Metal components tested with sand had a more worn aspect than those tested without sand due to the continuous projection of sand on the fastening system, as seen in Fig. 17. The screws show a very pronounced wear on the edges of the head, while the coating of the clips have a matte appearance unlike the clips tested without sand that have the original appearance of the coating, brighter. But in no case are discontinuities seen in the coating. The appearance of the metal components after the test in a saline mist chamber for 175 h are shown in Fig. 18. It can be seen that there is no big difference between the components tested with and without sand. The main points of corrosion in the screw correspond to the edges of the head, where the screw touches against the torque wrench in the operation of tightening of the system, and, also, the washer that touches with the lower side of the head of the screw at the top and the clip at the bottom. Referring to the clip, the maximum corrosion point corresponds to the contact area with the washer, because in that area the protective coating peels in the operation of tightening. The new clip without tightening is removed from the saline mist chamber without pitting corrosion.
Fig. 16. Static mechanical behaviour of flanged plates.
Fig. 17. Appearance of metal components after the dynamic test (prior to introduction in the saline mist chamber). (a) Tested without sand, (b) with sand.
Fig. 18. Appearance of metal components after 175 h in saline mist chamber. (a) Tested without sand, (b) tested with sand and (c) new (non tested).
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However, the new screw only retains the original coating in areas away from the edges. 5. Conclusions The thermoplastic elastomer selected for the rail pad withstands the dynamic load test with hardly any mechanical deterioration for both the laboratory situation, according to the standard, and the situation in the presence of sand. During the dynamic test, the horizontal displacements of the rail head increased in the presence of sand, while the vertical displacements deceased. These results are corroborated by the increase in the remaining displacements and the increase in the stiffness of the set in the situation tested in the presence of sand. An increase of over 44% in this last parameter would not allow this fastening system to comply with the existing regulations. These modifications in behaviour are due to the introduction of sand in the gaps among the oblongs of the plate on the upper face in contact with the rail. This situation could be improved by means of the redesign of the plate, closing off the possibility of the entrance of sand on the upper face in the same way that it is closed off in the lower part, where no sand enters, by means of a perimeter nerve. It should be noted that the component most deteriorated by wear was not one of the components of the fastening system but rather the sleeper itself, where grooves of up to 0.4 mm depth appeared. Finally, the mechanical properties of the flanged plate and the behaviour against severe environmental conditions of the metal components of the fastening system have not been significantly affected by the presence of sand.
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[11] D. Milenkovic, Z. Adamovic, D. Zlatkovic, M. Krstic, D. Milutnovic, Optimisation of adhesion force of screwa, rail fittings ‘SQL-14’ on concrete sleepers, J. Balkan Tribol. Assoc. 19 (3) (2013) 401–411. [12] J.A. Zakeri, R. Abbasi, Field investigation of variation of loading pattern of concrete sleeper due to ballast Sandy contamination in Sandy deserta reas, J. Mech. Sci. Technol. 26 (12) (2012) 3885–3892. [13] C. Paiva, M. Ferreira, A. Ferreira, Ballast drainage in Brazilian railway infrastructures, Constr. Build. Mater. 92 (2015) 58–63. [14] J.A. Zakeri, Investigation on railway track maintenance in Sandy-dry areas, Struct. Infrastruct. Eng. 8 (2) (2012) 135–140. [15] M.M. Mirahmedov, M.K. Muzaffarova, Expansión of a scope of method protection the railways from entering by sand, Transp. Prob. 8 (2) (2013) 55–61. [16] A. Watson, The control of wind blow sand and moving dunes: a review of the methods of sand control in deserts, with observation from Saudi Arabia, Q. J. Eng. Geol. 18 (3) (1985) 237–252. [17] X.R. Li, H.L. Xiao, M.Z. He, J.G. Zhang, Sand barriers of Straw checkerboards for hábitat restoration in extremely arid desert regions, Ecol. Eng. 28 (2) (2006) 149–157. [18] Z. Dong, G. Chen, X. He, Z. Han, X. Wang, Controlling blow sand along the highway crossing the Taklimakan desert, J. Arid Environ. 57 (2004) 329–344. [19] K.C. Zhang, J.J. Qu, K.T. Liao, Q.H. Niu, Q.J. Han, Damage by wind-blow sand and its control along Qinghai-Tibet Railway in China, Aeolian Res. 1 (2010) 143– 146. [20] J.J. Cheng, C.X. Xue, The sand-damage-prevention engineering system for the railway in the desert región of the Quinghai-Tibet plateau, J. Wind Eng. Ind. Aerodyn. 125 (2014) 30–37. [21] Y. Yang, W. Liu, H. Liu, Y. Liu, Research on the construction and effect of sandprevention system in typical section of Taiyuan-Zhongwei-Yinchuan Railway, China Railway Sci. 38 (1) (2014) 13–20. [22] ADIF, Vía. Especificación Técnica, ET 03.360.571.8, Traviesa Monobloque de Hormigón Pretensado, 4ª ed., Enero 2009. [23] UNE-EN 13481-2, Railway applications. Track. Performance requirements for fastening systems. Part 2: Fasteninig systems for concrete sleepers, 2010. [24] I.A. Carrascal, Optimización y análisis de comportameinto de suistemas de sujeción para vías de ferrocarril de Alta Velocidad Española (PhD thesis), Universidad de Cantabria, 2006. [25] ADIF, Vía. Especificación Técnica, ET 03.360.573.4, Vaina antigiro extraíble y Tirafondo AV-1, 1ª ed., Septiembre 2009. [26] EN 13230-2:2009, Railway applications. Track. Concrete sleeper and beares. Part 2: Prestressed monoblock sleepers, 2009. [27] ADIF, Vía. Especificación Técnica, ET 03.360.578.3, Placas acodadas ligeras de sujeción, 1ª ed., Mayo 1998. [28] ADIF, Vía. Especificación Técnica, ET 03.360.570.0, Placas elásticas de asiento para sujeción VM, 1ª ed., Diciembre 2005. [29] M. Sol-Sanchez, F. Moreno-Navarro, M.C. Rubio-Gámez, The use of elastic elements in railway tracks: a state of the art review, Constr. Build. Mater. 75 (2015) 293–305. [30] I.A. Carrascal, J.A. Casado, J.A. Polanco, F. Gutiérrez-Solana, Dynamic behaviour of railway fastening setting pads, Eng. Fail. Anal. 14 (2007) 364–373. [31] RENFE, ET 03.360.564.1, Especificación Técnica para el suministro de Clips Elasticos para sujeción de carril, 1ª ed., Junio 1981. [32] H. Steward Edgel, Arabian Deserts: Nature, Origin and Evolution, Springer, Netherlands, 2006. [33] H. Besler, The north-eastern Rub al Khali within the borders of the United Arab Emirates, Z. Geomorphol. 26 (4) (1982) 495–504. [34] M.M. Abu-Zeid, A.R. Baghdady, H.A. El-Etr, Textural attributes, mineralogy and provance of sand dune fields in the greater ASl Ain area, United Arab Emirates, J. Arid Environ. 48 (4) (2001) 475–499. [35] E. Garzanti, P. Vermeasch, S. Andó, G. Vazzoli, M. Valagussa, K. Alle, K.A. Kadi, A.I.A. Al-Juboury, Provenance and recycling of Arabian desert sand, Earth Sci. Rev. 120 (2013) 1–19. [36] M. Elipe, S. López-Querol, Aeolian sands: characterization, options of improvement and possible employment in construction – The state of the art, Constr. Build. Mater. 73 (2014) 728–739. [37] UNE-EN 13416-9+A1, Railway applications. Track. Test methods for fastening systems. Part 9: Determination of stiffness, 2012. [38] UNE-EN 13416-4, Railway applications. Track. Test methods for fastening systems. Part 4: Effect of repeated loading, 2012. [39] UNE-EN 13416-5, Railway applications. Track. Test methods for fastening systems. Part 6: Effect of severe environmental conditions, 2012. [40] UNE-EN ISO 9227, Corrosion tests in artificial atmospheres. Salt spray tests, 2012. [41] ADIF, Plano P16.5076.00, Placa PAE-2 para sujeción VM UIC 60, 2005.
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Dynamic behaviour of high-speed rail fastenings in the presence of desert sand I.A. Carrascal ⇑, J.A. Casado, S. Diego, J.A. Polanco LADICIM (Laboratory of Materials Science and Engineering), University of Cantabria, E.T.S. de Ingenieros de Caminos, Canales y Puertos, Av/Los Castros 44, 39005 Santander, Spain
h i g h l i g h t s Fastening system characterisation for railway under extreme conditions (sandstorms). The tested fastening system is not designed to work in the presence of sand. A slight change in the rail pad design could improve its dynamic behaviour in sand. The presence of sand modifies the mechanical properties of the fastening system. The sand does not affect the mechanical properties of individual system components.
a r t i c l e
i n f o
Article history: Received 28 October 2015 Received in revised form 2 May 2016 Accepted 5 May 2016 Available online 12 May 2016 Keywords: Sand Fastening Fatigue Wear Rail pad Railway High speed
a b s t r a c t High-speed lines in Saudi Arabia are subjected to sandstorms. These environmental conditions are not established at laboratory level. This work studies the influence of the presence of sand on the dynamic behaviour of the fastening system. So the evolution of the system is analysed under simulated sandstorm conditions and it is compared with the standard one. Results indicate that the presence of sand in the fastening system generates wear on the sleeper and increases the stiffness after the fatigue test. However, this fact does not modify both the mechanical behaviour and the durability of the individual elements. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction Saudi Arabia has set itself the challenge of designing and building a high-speed railway line, with a UIC gauge double electrified track layout, for speeds of 320 km/h. The line runs between the cities of Medinah and Makkah-Harum (Mecca), covering 444 km in the west of the Arabian Peninsula, and the journey will take less than 3 h [1,2]. The main technical challenge for this engineering work is the highly adverse climatic and geological conditions, the line passes through stretches of dunes, sand and strong winds Abbreviations: FSi, load applied in the static stiffness test; dS, displacement measured in the static stiffness test; kS, vertical static stiffness; FLFPi, load applied in the dynamic stiffness test; dLFP, displacement measured in the dynamic stiffness test; kLFP (i), dynamic stiffness at a frequency of i Hz; dvp, the vertical rail basement displacement; dhc, the horizontal rail head displacement. ⇑ Corresponding author. E-mail address: [email protected] (I.A. Carrascal). http://dx.doi.org/10.1016/j.conbuildmat.2016.05.023 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.
which may cause the occurrence of sandstorms, as well as some sharp temperature changes between day and night. The presence of sand will affect many of the components of the track superstructure, whether ballasted or ballastless track [3,4]. In recent years, the effect of the presence of sand on the rail has been analysed, either on the wheel-rail contact wear [5–10]. The pull-out force goes up significantly, due to, the increase in friction when the injected binder has the addition of quartz sand [11]. The influence of flowing sand grains among the ballast aggregates increases the stiffness of ballast layer, consequently, rail support modulus increases, so the received share of total axle load subsequently, increases on the sleeper which is placed under the wheel load [12,13]. At present there is great concern over the maintenance of the track in the presence of sand and in this respect, a great deal of research has been undertaken on how to prevent the action of the sand by keeping it away from the track [14–21].
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The aim of this work is to verify the influence that the presence of sand may have on the dynamic behaviour of the rail fastening system. For this purpose, a well-known and tested system has been selected, which is the one which is being used in Spain in the newest stretches of the AVE (Spanish high-speed train). The study analyses the evolution of the fastening behaviour, once the system has been subjected to a fatigue test, that reproduces the inclined loads expected when the trains circulates on the track. A comparison will be made between the laboratory situation, which will be the model fastening, and another situation with the presence of sand, in an attempt to simulate in the laboratory a pseudo-sandstorm on the fastening system while it is subjected to the fatigue test. Another objective of the work is the development of the dynamic test in the presence of sand, for which it will be necessary to design a system for conducting and projecting the sand on the fastening system tested. 2. Material For the test set-up, a monoblock prestressed concrete sleeper, ADIF AI-04-AD [22], was selected, equipped with a removable non-rotating insert. The behaviour of the model fastening on one of the sleeper supports was observed, tested under normal laboratory conditions and then, on the other support, an equivalent fastening system was tested but in the presence of sand. The two fastening sets have been considered to be within the D category defined by Standard EN 13481-2 [23]. These fastening sets were intended for lines with curves of a large radius, often used for high-speed trains, and with a typical axle load of 180 kN, a typical curvature radius of 800 m, a rail coupon 60E1, a typical space between sleepers or supports of 600 mm and any typical maximum speed. The fastening system selected for the tests is a modification of the one used in the Madrid-Barcelona AVE which is fitted with the VM fastening system [24]. The modification consists of the replacement of the VAPE dowel-screw system with a removable anti-rotation dowel with an AV-1 lag screw [25]. Therefore, the components of the fastening system are (see Fig. 1):
Sleeper: ADIF AI-04-EA (prestressed concrete monoblock) [22,26]. Flanged plate: A2 (Polyamide 66 + 35 GF) [27]. Rail pad: PAE-2 (Thermoplastic Elastomer, TPE) [28–30]. Insert: removable anti-rotation AV-1 (PA 6.6 + 35 GF) [25]. Screw: AV-1 [25]. Clip: SKL-1 [31].
The other basic element in the present work is sand, the material which must interact with the fastening system while it is in operation. The sand selected should be as similar as possible in size and composition to that found in the desert of Arabia [32–36]. A mixture was made of equal parts of silica sand and sand taken from the Sardinero beach in Santander, with fractions in the range of 0.04–0.4 mm. Table 1 shows the granulometry of the sand.
3. Test methodology In order to analyse the influence of the presence of sand on the dynamic behaviour of the fastening system, the variation in a
Table 1 Granulometry of the sand. Sieve size [mm]
Passing [%]
0.5
0.4
0.25
0.125
0.063
99.9
99.6
28.9
4.3
1.32
series of parameters was evaluated, measured before and after performing a fatigue test on two identical sets, equipped with the same components, but with one under normal laboratory conditions and the other under extreme conditions with presence of sand. In addition to the evolution of the test itself, another way of assessing the damage caused by the fatigue test on the system is to analyse the individual behaviour and the joint behaviour of the various constituents that make up the fastening system. In this case, the stiffness of the rail pad was evaluated both separately and as a whole. For the evaluation of the rigidities, static and dynamic vertical tests were performed on the rail pad and the fastening set according to standard EN 13416-9 [37], as can be seen in Fig. 2a,b. In order to carry out the vertical static stiffness test on the plate and the set, a series of 3 compression load and unload cycles was applied at a speed of 120 kN/min from a minimum value, FS1 = 18 kN, to a maximum of FSmax = 85 kN [23]. The vertical rail displacement (d) was recorded for the 3 cycles as the average of four LVDT transducers placed at each corner of the plate, and the vertical static stiffness (kS) was measured in the load branch during the third cycle according to expression (1) between the strength values FS1 = 18 kN and FS2 = 0,8FSmáx = 68 kN. The test set-up was the same as that of the above test:
kS ¼
F S2 F S1 dS
ð1Þ
dS being the difference of the displacement between the load values FS1 and FS2. In order to carry out the vertical dynamic stiffness tests, with the same set-up as in the static test, 1000 sinusoidal wave cycles were applied between the values of FLFP1 = 18 kN and FLFPmax = 85 kN [23] at the frequencies of 5, 10 and 20 Hz. With the average obtained in the last 10 cycles, the dynamic stiffness (kLFP) was determined according to expression (2)
kLFP ð5=10=15 HzÞ ¼
F LFPmax F LFP1 dLFP
ð2Þ
dLFP being the difference between the displacement between the load values FLFP1 and FLFPmax. The fatigue tests were performed according to standard UNE-EN 13416-4 [38], applying 3 million sinusoidal cycles at a frequency of
Fig. 1. Fastening system tested.
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Fig. 2. Test set-up. Stiffness tests: (a) on rail pad and (b) on fastening set. (c) Cyclic load test.
5 Hz under inclined load between the values of 5 and 70 kN (see Fig. 2c). By means of 6 LVDT transducers, the vertical rail basement displacement, dvp, and the horizontal rail head displacement, dhc, was measured. The inclination angle of the actuator was set at 26°. The fatigue test was carried out on one of the sleeper heads in laboratory conditions, but on the other some extreme conditions were designed with the presence of both sand and of a cloud of the finest fraction of sand caused by a continuous recirculation, an effect which is similar to the environmental conditions to which the fastening set may be subjected in a desert. In the fatigue test with presence of sand, the recirculation of the sand is achieved by using compressed air at a pressure of 8 bars obtaining, by means of the Venturi effect, an aspiration of sand and its subsequent propulsion onto the fastening set (see Fig. 3). As can be observed, a hopper is placed under the sleeper which collects the sand projected onto the fastening set and refeeding the compressed air circuit to send it back to the system. This sand-propelling system was connected an average of 10 h a day.
After completing the fatigue test, the stiffness tests were repeated both on the set and on the plate. The system was not cleaned after the fatigue test to undertake the system stiffness test and it was only cleaned when the system was dismantled in order to perform the tests on the rail pad. Due to the suspicion that the sand could damage any other part of the fastening system, two more tests were planned to carry out in order to verify its effect on the flanged plates and on the corrosion protection of metal components. The lower surface of the flanged plate can erode the concrete of the sleeper, and this effect increases with the presence of the sand during a dynamic test. Static tests up to failure on the outer flanged plates of the two tests, with and without sand, were performed to analyse whether the possible erosion of the nerves in the lower surface affects their mechanical behaviour. The results of these tests were compared with those obtained with the original flanged plates injected into the same mold cavity.
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Fig. 3. Cyclic load test set-up for the configuration with sand recirculation set-up.
The tests were performed in a vertical device that simulates the geometries of the sleeper and the UIC 60 rail foot. Each flanged plate was placed on the sleeper simulator with the corresponding screw, nut and clip, applying a torque of 120 Nm. Then the loading process was executed at a rate of 1 kN/s until the breakage of the flanged plate was obtained. Fig. 4 shows the testing device mounted on a servohydraulic testing machine with 250 kN of capacity. Finally, a corrosion test in a saline mist chamber where a salt water (5% NaCl) solution is atomised at 35 °C by means of spray nozzles using pressurised air during 175 h [39,40] was prepared, considering that the sand might erode the protective layer of the metal components of the fastening system. The metallic elements exposed to saline mist were screws and clips obtained from the two tested fasteners and the same components, not tested previously, in order to compare results. In summary, Table 2 shows the planning of the tests performed in the study, and the sequence in which they were executed. All the tests were performed both at laboratory conditions and under the presence of sand.
Table 2 Testing plan. Components
Test
Pad
1. Vertical static stiffness test 2. Vertical dynamic stiffness test (5/10/20 Hz)
Assembly
3. Vertical static stiffness test 4. Fatigue tests under inclined load (3106 cycles) 5. Vertical static stiffness test
Pad
6. Vertical static stiffness test 7. Vertical dynamic stiffness test (5/10/20 Hz)
Flanged plate Clip and screw
8. Static compression test 9. Corrosion test in a saline mist chamber
4. Results and analysis 4.1. Fatigue tests under inclined load All displacements were recorded throughout the fatigue test, both the horizontal displacement of the rail head and the vertical
Fig. 4. Device for the mechanical characterisation of the flanged plate A2.
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displacement of the rail foot. The graph in Figs. 5 and 6 show the evolution of both parameters over the 3 million cycles for both the model system and the system tested with sand. As can be observed, there is a clear increase in the horizontal displacement of the rail in the system tested with sand, or, in other words, an increase in the line gauge, while there is little change in the vertical displacement, this being slightly higher for the system tested without sand. If, however, stiffness results are analysed, it can be seen that the horizontal stiffness hardly vary at all for the configurations with and without sand, whereas it is the vertical stiffness (see Fig. 7) which shows a significant difference between the two configurations, the stiffness of the system with sand being around 20% higher. The results of the fatigue test are evaluated in terms of the remaining displacements induced between the first test cycles and the last ones after 3106 cycles. Figs. 8 and 9 show the comparison between the first and last cycles for both the horizontal displacement of the head and the vertical displacement of the foot for the two systems tested, with and without sand. Table 3 shows the values of the remaining displacements between the first and last cycles under the maximum and the minimum loading cycles. As can be observed, the vertical displacements are of a very small absolute value, showing hardly any differences between
Fig. 7. Evolution of vertical dynamic stiffness during fatigue test.
hc
Rail head displacement, δ [mm]
1,5
δ
1
δ δ δ
(without sand)
hc,min hc,max hc,min
(without sand)
(with sand)
hc,max
(with sand)
0,5
Fig. 8. Remaining horizontal displacements of the rail head.
0 0
5 10 5
1 10 6
1,5 106
2 10 6
2,5 106
3 10 6
Cycle Fig. 5. Horizontal rail head displacements during fatigue test, dhc.
Fig. 9. Remaining vertical displacements of the rail foot.
Fig. 6. Vertical rail foot displacements during fatigue test, dvp.
the tests with and without sand. Meanwhile, the horizontal displacements of the rail head are of a certain magnitude, being moreover significantly higher in the case of the test sand, 136% for the maximum strength and 40% for the minimum strength.
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Despite the increase in displacement recorded by the rail head in the set-up with sand, the measured values remain within the range of validity, which, according to the technical specification files, is 1 mm. 4.2. Stiffness vertical test on rail pad The rail pads, prior to being mounted, were characterised independently of the fastening system by means of a static and dynamic test at different frequencies. The graph in Fig. 10 shows the evolution of the third of the load cycles applied in the static stiffness test, the cycle in which the measurement of the static stiffness of the plate was made, both for the test prior to the fatigue test and for the subsequent one for the two fastening systems, the model one and the one with sand. It can be seen from the figure that the influence of the presence of sand on the rail pad has been minimal as regards its static behaviour, remaining at all times below a 25% increase, which is the threshold established by the standard currently in use. If the dynamic behaviour is analysed, the results are similar to those obtained in the static test, that is, there are hardly any variations between the initial tests and the tests after the fatigue, as can be observed in the graph in Fig. 11. Table 4 shows in brief the stiffness values obtained for the rail pads before and after the dynamic test for the two set-ups tested. It can be observed that in all cases, there is a slight softening after the dynamic test. 4.3. Stiffness vertical test on the whole fastening system
Fig. 11. Dynamic behaviour of the rail pad.
Table 4 Stiffness of the rail pads tested. Test
Static Dynamic Dynamic Dynamic Dynamic
Stiffness [kN/mm]
(5 Hz) (10 Hz) (20 Hz) (average)
Before dynamic
Without sand after dynamic
With sand after dynamic
133.7 159.2 162.3 183.8 168.7
129.9 151.0 158.7 176.7 162.1
133.3 154.8 162.3 180.5 165.9
(2.8%) (5.2%) (2.2%) (3.9%) (3.9%)
(0.3%) (2.8%) (0.0%) (1.8%) (1.7%)
A static vertical test was performed on the behaviour of all of the system without changing anything, except for a surface cleaning of the sand that had been left on the fastening system. The graph in Fig. 12 shows the evolution of the third of the load cycles applied in the stiffness test, the cycle in which the measurement of the static stiffness is made on the whole system, both for the test prior to the fatigue and for the subsequent one for the two test set-ups used.
Table 3 Remaining displacements.
DFmax DFmin
Without sand [mm]
With sand [mm]
dhc
dvp
dhc
dvp
0.19 0.36
0.02 0.06
0.45 0.50
0.02 0.03 Fig. 12. Static behaviour of the system.
Table 5 Static stiffness of the fastening system. Stiffness [kN/mm] Without sand
Fig. 10. Static behaviour of the rail pad.
With sand
Before dynamic
After dynamic
Before dynamic
After dynamic
158.2
170.1 (7.5%)
170.3
246.3 (44.6%)
Table 5 shows in brief the stiffness values obtained for the fastening set before and after the dynamic bending load test for the two set-ups tested. In this case, it is verified that in both cases, after the dynamic test, the set stiffness, increasing by up to 44.6% in the case of the test with sand, thus exceeding 25%, the limit established for a correct behaviour of the system.
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The justification for this sharp increase in stiffness could be found on dismantling the fastening system. It could be verified that although the sand widely penetrated between the ribs under the flanged plate (Fig. 13), it could not do this under the rail pad except in one of the corners and in the side edges in contact with the flanged plate, Fig. 13a. In contrast, the photograph of Fig. 13b
Fig. 13. Aspect of the fastener once the fatigue test with sand is finished. (a) Under rail pad, (b) upper face of the rail pad.
shows how the sand settled widely in the gaps between the oblongs of the upper face of the rail pad, in contact with the rail plate. The cause for which the sand is introduced in the relief of the upper face and not of the bottom face of the rail pad lies in its own geometry. If the scheme of the rail pad [41] (Fig. 14) is analysed it is found that in the lower face, in contact with the concrete of the sleeper, there is a peripheral nerve that closes the contour of the rail pad and keeps out the sand except for a small amount that is introduced due to the displacement caused by the fatigue test. By contrast, in the upper face, which is in contact with the rail foot, the peripheral nerve does not exist and the sand is able to penetrate. The rail pad is designed so that the channels can function as drainage and, even, as a cooling system for the pad under the action of repeated loads that could generate heat and change its mechanical properties. However, rail pads are not designed to work in the presence of particulate matter, as may be the case in a desert. This is the fact that justifies the increase in stiffness after the dynamic test since the sand that occupies the gaps prevents the correct strain of the plate under loading. Finally, it can be observed in Fig. 15 that, after the dynamic test with sand, the sleeper suffers from wear in the zones that coincide
Fig. 15. Wear produced on the sleeper in the fatigue test with sand.
Fig. 14. Detail of the open areas in the rail pad [41].
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with the nerves of the flanged plate and the outer edge of the rail pad. The depth of the grooves generated on the concrete reaches values of up to 0.4 mm. Similarly, the outer flanged plate tested in sand also had some slight wear, visible with the naked eye, on the surface of the nerve in contact with the sleeper. This wear pushes down the flanged plate and thus lowers the point of support of the clip loop, leading to a loss in clamping force which may be the cause of the increase in the horizontal displacement of the rail head during the fatigue test. 4.4. Static compression test on the flanged plate A2 As mentioned above, the outer flanged plate tested with sand showed appreciable wear that only affected the surface roughness,
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but in no case has the resistant section of the nerves of the plate changed. Fig. 16 shows that three million cycles do not imply any change in the mechanical behaviour of the two plates tested with and without sand with respect to the original plates. 4.5. Test of severe environmental conditions on metallic components Metal components tested with sand had a more worn aspect than those tested without sand due to the continuous projection of sand on the fastening system, as seen in Fig. 17. The screws show a very pronounced wear on the edges of the head, while the coating of the clips have a matte appearance unlike the clips tested without sand that have the original appearance of the coating, brighter. But in no case are discontinuities seen in the coating. The appearance of the metal components after the test in a saline mist chamber for 175 h are shown in Fig. 18. It can be seen that there is no big difference between the components tested with and without sand. The main points of corrosion in the screw correspond to the edges of the head, where the screw touches against the torque wrench in the operation of tightening of the system, and, also, the washer that touches with the lower side of the head of the screw at the top and the clip at the bottom. Referring to the clip, the maximum corrosion point corresponds to the contact area with the washer, because in that area the protective coating peels in the operation of tightening. The new clip without tightening is removed from the saline mist chamber without pitting corrosion.
Fig. 16. Static mechanical behaviour of flanged plates.
Fig. 17. Appearance of metal components after the dynamic test (prior to introduction in the saline mist chamber). (a) Tested without sand, (b) with sand.
Fig. 18. Appearance of metal components after 175 h in saline mist chamber. (a) Tested without sand, (b) tested with sand and (c) new (non tested).
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However, the new screw only retains the original coating in areas away from the edges. 5. Conclusions The thermoplastic elastomer selected for the rail pad withstands the dynamic load test with hardly any mechanical deterioration for both the laboratory situation, according to the standard, and the situation in the presence of sand. During the dynamic test, the horizontal displacements of the rail head increased in the presence of sand, while the vertical displacements deceased. These results are corroborated by the increase in the remaining displacements and the increase in the stiffness of the set in the situation tested in the presence of sand. An increase of over 44% in this last parameter would not allow this fastening system to comply with the existing regulations. These modifications in behaviour are due to the introduction of sand in the gaps among the oblongs of the plate on the upper face in contact with the rail. This situation could be improved by means of the redesign of the plate, closing off the possibility of the entrance of sand on the upper face in the same way that it is closed off in the lower part, where no sand enters, by means of a perimeter nerve. It should be noted that the component most deteriorated by wear was not one of the components of the fastening system but rather the sleeper itself, where grooves of up to 0.4 mm depth appeared. Finally, the mechanical properties of the flanged plate and the behaviour against severe environmental conditions of the metal components of the fastening system have not been significantly affected by the presence of sand.
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