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YOUNG SCIENTIST 2017
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Study of longitudinal restraint of rail fastenings
Helga Papp, Nándor Liegner
Budapest University of Technology and Economics
Faculty of Civil Engineering, Department of Highway and Railway Engineering
e-mail: papp.helga@epito.bme.hu, liegner.nandor@epito.bme.hu
Abstract
The superstructure of railway track is set out to significant internal forces so there are separate technological
regulations that refer to the determination of technological parameters of certain structural elements and to their
minimal values. This study shows the possibility that performing measurements that are different from the standard
disposal and process we can get more accurately acquainted with the behaviour of certain superstructural elements.
We demonstrate the analysis of rail restraint of a type of rail fastening by standard and in non-standard ways as
well. The standard measurement results can be used for analysing effects of temperature change. The results of
non-standard measurements with vertical load can be used for breaking and accelerating analysis.
Key words: rail restraint, longitudinal, stiffness, measurement, rail fastening
1 Longitudinal forces and displacements occurring in the railway track
The change of temperature, breaking and accelerating forces of trains cause longitudinal
displacements and normal forces.
In case of superstructural ballasted tracks with sleepers, the restraint of ballasted track with
sleepers and the rail restraint of used rail fastening system mean the longitudinal restraint. The
available longitudinal restraint of ballasted track is limited by the requirements for ballast
material and the regulations for realization [1].
However the behaviour of longitudinal effects of rail fastenings shows significant differences
and varies considerably for each type. So for mechanical calculations it is necessary to know
the features and behaviour of used rail fastening system even more accurately.
2 Measuring arrangements
Test series have been carried out in the Laboratory of the Department of Highway and Railway
Engineering, Budapest University of Technology and Economics. The rail displacement was
measured with inductive transducer of type Hottinger Baldwin Messtechnik (HBM) WA20 mm
and the load was measured with force transducer of type HBM Quantum MX 840, evaluation
software was Catman AP.
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The procedure of determining rail restraint is stated in standard EN 13146-1:2012+A1:2014
[2]. Measurements taken according to the standard are not set to vertical load. With the help of
measured rail restraints certain rail fastening systems can be compared, but we cannot say that
rail fastening systems with higher rail restraint unequivocally better or worse than others. At
certain configurations the optimum of longitudinal restraint of rail fastening systems can be
determined by the experiences, calculations and models obtained during the operation.
Longitudinal displacements can be formed under tensile force or compressive force.
Compressive force in rail evolving from temperature change in summer can lead to buckling of
rails and tensile force in winter can lead to fracture of rails. [3] It is worth analysing if significant
difference can be noticed in the behaviour of rail and rail fastening while pulling or pushing.
The effect of temperature change can occur on unloaded track (too). However, at the same time
with braking and accelerating force, the dead weight of craft causes significant strain on the
track, too. In case of substantial vertical load, longitudinal restraint of rail will not be equal to
the unloaded one. In our study we analyze how longitudinal restraint of a selected type of rail
fastening depends on vertical load, use of rail joint shims and on applying tensile or compressive
load on the rail itself. In addition to rail restraint calculated by the regulation, it is worth
comparing the maximal longitudinal forces taken by the rail fastening, as the rail will slip in the
fastening exceeding this force. Based on the standard a rail long enough needs to be fastened
on the sleeper as it is built into the track. A fixed support has to be provided for the sleeper,
preventing displacements running in parallel with the rail. Tensile load with 10 ±5 kN/min
increase has to be exposed on the rail. When the rail slips in the rail fastening, the force has to
be reduced to 0 kN. After ending tensile load, longitudinal displacement of rail has to be
measured for 2 more minutes [2].
Demonstrated analyzed cases (most of them are different from the standard):
• pulling of rail without vertical load;
• pushing of rail, without vertical load;
• pulling of rail and with 20 kN, 40 kN, 60 kN, 80 kN, 100 kN vertical load;
• pushing of rail and with 20 kN, 40 kN, 60 kN, 80 kN, 100 kN.
At first we determined the value of standard rail restraint of the analyzed rail fastening. The test
needs to be carried out 4 times and the first result needs to be ignored [2]. The test arrangement
is shown in Figure 1.
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Figure 1: The test arrangement
The force-displacement diagrams obtained from the measurement can be seen in Figure 2.
Figure 2: Measurement of rail restraint according to the standard
After disregarding the first measurement, the average value of rail restraint was 17.9 kN. During
the measurements the rail in the fastening slipped averagely by tensile load of 18.6 kN.
The measurement arrangement with vertical load is shown in Figure 3.
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Figure 3: The test arrangement (with vertical load)
About measurements, carried out with vertical load higher than 20 kN, it can generally be said
that a well visible platform (horizontal sections) was not formed on the force-displacement
diagram. The rail with constant tensile load did not slipped in the rail fastening slowly, but
suddenly shifted (E.g. Figure 4). Because of its appearance and comparability in practice,
further on we compared those tensile or compressive loads, effect of which in the rail fastening
system for the first time increased sharply.
Figure 4: Pulling of rail, 40 kN vertical load
The maximum tensile and compressive loads obtained during the performed tests are
summarized in the Table 1.
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Table 1: Maximum tensile and compressive forces
Vertical
load
0 kN
20 kN
40 kN
60 kN
80 kN
100 kN
In case of
pulling the
rail
19
26
30
38
31
34
In case of
pushing
the rail
13
20
23
27
29
32
It is quite clear that the rail in the fastening got going by a smaller force every time while
pushing and not pulling the rail. This result may explain the nature of rail creep. By increasing
the vertical load, the vertical compressive force was increasing as well. By increasing the
vertical load, the tensile load applied on rail does not show monotonous increase or decrease.
The necessary tensile load for sudden displacement in rail fastening, at 60 kN vertical load was
the highest (38 kN).
3 Conclusion
We need more similar tests of different-typed pointwise fastenings to come to a general
conclusion in connection with the behaviour of pointwise fastenings. In this article we
demonstrated that tests, that are different from the standard ones, can signify valuable
information in connection with the maintenance of track/about track maintenance.
References
[1] Coenraad Esveld, A better understanding of continuous welded rail track. Rail Engineering
International Edition, vol. 25, 1996, no 4, p. 13-16
[2] EN 13146-1:2012+A1:2014, European Standard, Railway applications, track, test methods
for fastening systems, Part 1, Determination of longitudinal rail restraint, European
Committee for Standardization, ICS 93.100, 2012.
[3] Sung Wen-pei, Shih Ming-hsiang, Lin Cheng-I, Go Cheer Germ, The critical loading for
lateral buckling of continuous welded rail. Journal of Zhejiang University SCIENCE A. vol.
6, 2005, no. 8, p. 878-885
