ISO/TS 18973:2025

Technical
Specification
ISO/TS 18973
First edition
Railway infrastructure — Rail
2025-04
fastening systems — Two
directional test method for
resistance to repeated loading
Infrastructure ferroviaire — Systèmes d'attache — Méthode
d’essai bidirectionnel pour la determination de résistance aux
charges répétitives
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 1
5 Principle . 3
6 Apparatus . 4
6.1 General arrangement .4
6.2 Rail .4
6.3 Actuator .5
6.4 Load application head .6
6.5 Displacement measuring instruments .6
6.5.1 Calibration procedure.6
6.5.2 Calibration requirement .6
6.5.3 Fixtures for mounting displacement measuring instruments .6
6.6 Force measuring instruments .6
6.6.1 Instruments .6
6.6.2 Verification of calibration . . .6
6.7 Strain gauges for rail clips .6
7 Test specimens . 6
8 Test procedure . 7
8.1 General .7
8.2 Preparation for test .7
8.3 Clamping force and uplift stiffness .7
8.4 Longitudinal rail restraint .7
8.5 Vertical stiffness .7
8.6 Lateral stiffness .7
8.7 Calculation of test loads and test loading angles .8
8.8 Two directional static load test .8
8.8.1 Preparation for the static load test .8
8.8.2 Loading procedure .10
8.8.3 Results required from the static load test .11
8.9 Two directional repeated load test . 12
8.9.1 Preparation for the repeated load test . 12
8.9.2 Loading conditions of the repeated load test. 12
8.9.3 Results required from the repeated load test . 13
8.9.4 Repeat tests . . 13
9 Test report . 14
Annex A (normative) Test method for lateral stiffness .15
Annex B (informative) Calculation method of test loads and test loading angles . 19
Bibliography .28

iii
Foreword
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iv
Technical Specification ISO/TS 18973:2025(en)
Railway infrastructure — Rail fastening systems — Two
directional test method for resistance to repeated loading
1 Scope
This document describes a test procedure for the determination of resistance to repeated loading by –
amongst others – applying out-of-phase load cycles which generate forces in two directions, representative
of those caused by traffic on railway track, taking into account the effect of two consecutive axles of passing
railway vehicles.
The document applies to surface mounted rail on sleepers, bearers and slab track.
The test procedure applies to a complete fastening assembly.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 22074-1, Railway infrastructure — Rail fastening systems — Part 1: Vocabulary
ISO 22074-2, Railway infrastructure — Rail fastening systems — Part 2: Test method for longitudinal rail
restraint
ISO 22074-4:2022, Railway infrastructure — Rail fastening systems — Part 4: Test methods for resistance to
repeated loading
ISO 22074-7, Railway infrastructure — Rail fastening systems — Part 7: Test method for clamping force and
uplift stiffness
ISO 22074-8:2022, Railway infrastructure — Rail fastening systems — Part 8: Test method for vertical stiffness
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 22074-1 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Symbols
Symbol Description First appearance
h height of loading position for normal rail, in mm; 6.2
N
h height of loading position for test rail, in mm; 6.2
T
P clamping force, in kN; 8.3
F maximum axial load on the rail without non-elastic displacement occurring, in kN; 8.4
F the lower limit of force for determining the static stiffness, in kN; 8.5
SA1
Symbol Description First appearance
F the reference force for measurement of static stiffness, in kN/mm; 8.5
SA max
k vertical stiffness of fastening assembly, in kN/mm; 8.5
SA
k lateral stiffness of fastening assembly, in kN/mm; 8.6
LA
e eccentricity of loading position from centre for test rail, in mm; 8.8.1
T
θ test loading angle applied from gauge side (A load), in radians; 8.8.1
A
θ test loading angle applied from field side (B load), in radians; 8.8.1
B
P test load applied from gauge side (A load), in kN; 8.8.2
A
P maximum test load applied from gauge side, in kN; 8.8.2
A max
P minimum test load applied from gauge side, in kN; 8.8.2
A min
P test load applied from field side (B load), in kN; 8.8.2
B
P maximum test load applied from field side, in kN; 8.8.2
B max
P minimum test load applied from field side, in kN; 8.8.2
B min
d lateral rail head displacement, in mm; 8.8.3
L
d measured lateral displacement at test rail head, in mm; 8.8.3
LH
d measured lateral displacement at test rail foot, in mm; 8.8.3
LF
φ tilting angle of test rail, in radians; 8.8.3
TR
h distance between two measuring points of lateral displacement, in mm; 8.8.3
TR
Q static wheel load for design, in kN; B.2
Q vertical component of the design load A (A load), in kN; B.2
A
Q vertical component of the design load B (B load), in kN; B.2
B
Y lateral component of the design load A (A load), in kN; B.2
A
Y lateral component of the design load B (B load), in kN; B.2
B
k total vertical stiffness per unit length, in kN/mm/m; B.2
v
k vertical stiffness of rail supporting structure, in kN/mm; B.2
SB
k total lateral stiffness per unit length, in kN/mm/m; 8.2
h
k lateral stiffness of rail supporting structure, in kN/mm; B.2
LB
W vertical component of the test load A (A load), in kN; B.2
A
W vertical component of the test load B (B load), in kN; B.2
B
H lateral component of the test load A (A load), in kN; B.2
A
H lateral component of the test load B (B load), in kN; B.2
B
A sleeper spacing, in m; B.2
EI vertical bending rigidity of normal rail, in kN∙m ; B.2
x
EI lateral bending rigidity of normal rail, in kN∙m ; B.2
y
φ rail tilting angle at the loading point for design load A, in radians; B.3
A
φ rail tilting angle at the loading point for design load B, in radians; B.3
B
M tilting moment of rail against the design load A, in kN∙m; B.3
A
M tilting moment of rail against the design load B, in kN∙m; B.3
B
C torsional rigidity of the normal rail, in kN∙mm /radian; B.3
e eccentricity of loading position from centre for normal rail, in mm; B.3
N
K’ torsional spring constant of the rail fastening system, in kN∙m/radian; B.3
K stiffness of rail pad, in kN/mm; B.3
K lower uplift stiffness of rail clip, in kN/mm; B.3
K higher uplift stiffness of rail clip, in kN/mm; B.3
P initial clamping force, in kN; B.3
P clamping force due to Q, Q or Q , in kN; B.3
1 A B
Symbol Description First appearance
P ’ clamping force on gauge side, in kN; B.3
P ’’ clamping force on field side, in kN; B.3
δ deflection of rail clip fastened on gauge side corresponding to (P ’−P ), in mm; B.3
1 0
d deformation of rail pad due to application of P , in mm; B.3
0 0
d deformation of rail pad due to application of Q, Q or Q , in mm; B.3
1 A B
b width of rail pad, in mm; B.3
b lateral distance between two clamping point, in mm; B.3
φ rail tilting angle at the loading point, in radians; B.3
φ rail tilting angle when clamping force is equal to initial clamping force, in radians; B.3
φ rail tilting angle when rail end begins to leave from rail pad, in radians; B.3
X width where bottom of the rail and the rail pad touch, in mm; B.3
Y deflection of rail bottom surface caused by increase in clamping force, in mm. B.3
5 Principle
Static and repeated loads of a constant amplitude are applied by a pair of actuators operating out of phase
with each other. This two directional loading testing is applicable when the fastening system is applied on
the railway track where out of phase lateral forces occur.
The test method for repeated loading is largely similar to the method defined in ISO 22074-4.
The test sequence is as shown in Figure 1.
First a normal rail is adopted for collecting data for calculating test loads.
Then a modified test rail is adopted in the two directional static load test and the repeated load test,
described in 8.8 and 8.9.
The test method cannot be applied to fastening systems which are based on web-supported rails nor to
embedded rails because they cannot be tested with modified test rails.

Figure 1 — Diagram of test sequence
6 Apparatus
6.1 General arrangement
The complete test procedure refers to several tests, for which specific test standards are applicable, which
define the specific test arrangements.
The arrangement for the two directional tests is described in 8.8 and 8.9.
6.2 Rail
All fastening assemblies used in the tests shall make use of a section of rail with a length of approximately
0,5 m and which shall be unlaminated and have neither loose rust on the surface nor be polished on the foot.

Use one of load application arrangement of the test rail shown in Figure 2. The test rail used in the two
directional tests, as described in 8.8 and 8.9, has the following features:
— The test rail with modified rail head (to accommodate the load application head) and shortened rail web
shall be as shown in Figure 2 a). The curve radius at the load application point is 15 mm unless otherwise
specified. The eccentricity of loading position from rail centre, e , is 30 mm unless otherwise specified.
T
— The test rail with partially removed rail web shall be as shown in Figure 2 b). The value X is the difference
between the height of loading position for the normal rail, h , and that for the test rail, h .
N T
— The foot of the test rail shall be identical to the foot of the normal rail used in service.
— The height of the loading position for test rail, h is obtained using the process of calculation described
T,
in Annex B.
NOTE A normal rail is the rail for which the fastening assembly is designed.
a) Modified rail head and shortened rail web b)  Partially removed rail web
Key
1 height of loading position for test rail, h
T
2 eccentricity of loading position from rail centre, e
T
3 curve radius at loading position
4 centre of gauge corner radius
5 point of load application
6 part of web removed
Figure 2 — Test rails
6.3 Actuator
Specifications for the actuators used in each of the tests described in 8.3, 8.4, 8.5 and 8.6 shall be taken from
the test standards referenced in these subclauses.
The two actuators used in the two directional tests, as described in 8.8 and 8.9, have the following features:
— They shall each be capable of applying a force of up to 160 kN static as well as dynamic in a cyclical
manner at a frequency of 5,5 Hz. Hydraulic control of actuators shall be done so that the resultant vertical
components of load applied to the fastening assembly decreases to nearly 0 kN.
— The actuator equipment shall be able to apply the test load on the test loading angle with a tolerance of
+/− 1,0 degrees. In other words, the actuator shall have a hinge to meet the required test loading angle.

6.4 Load application head
The load application head used in the two directional tests, as described in 8.8 and 8.9, shall be as described
in ISO 22074-4:2022, 5.2.3.
6.5 Displacement measuring instruments
6.5.1 Calibration procedure
The calibration procedure for the displacement measuring instruments in the two directional tests, as
described in 8.8 and 8.9, shall be as described in ISO 22074-4:2022, 5.2.4.1.
6.5.2 Calibration requirement
The calibration requirement for the displacement measuring instruments in the two directional tests, as
described in 8.8 and 8.9, shall be as described in ISO 22074-4:2022, 5.2.4.2.
6.5.3 Fixtures for mounting displacement measuring instruments
The fixtures for mounting the displacement measuring instruments in the two directional tests, as described
in 8.8 and 8.9, shall be as described in ISO 22074-4:2022, 5.2.4.3.
6.6 Force measuring instruments
6.6.1 Instruments
The force measuring instruments in the two directional tests, as described in 8.8 and 8.9, shall be as
described in ISO 22074-4:2022, 5.2.5.1.
6.6.2 Verification of calibration
The verification of calibration in the two directional tests, as described in 8.8 and 8.9, shall be as described
in ISO 22074-4:2022, 5.2.5.2.
6.7 Strain gauges for rail clips
The use of strain gauges for rail clips in the two directional tests, as described in 8.8 and 8.9, is optional, and
may be required by the purchaser.
When a rail clip stress assessment is performed, one or more strain gauges are applied to obtain the principal
strain on a surface of a rail clip. The measured strain is converted into stress.
A single-axis strain gauge is acceptable if the principal stress direction is clear prior to testing. Otherwise,
an appropriate type of strain gauge, such as the three-element rosette strain gauge, is selected to obtain the
principal strain and its direction simultaneously.
7 Test specimens
For all tests, the fastening assemblies used in the tests shall be mounted on a sleeper or other rail support,
which shall be set on a horizontal bed directly or an inclined bed in order to be able to apply loads using the
actuators.
Specifications for the test specimen used in each of the tests shall be taken from the referenced test
standards.
The test specimen used in the two directional tests, as described in 8.8 and 8.9, shall have the following
features:
— sleeper or other rail support shall be as described in ISO 22074-4:2022, 5.3.1.
— fastening assembly shall be as described in ISO 22074-4:2022, 5.3.2.
8 Test procedure
8.1 General
The following procedure corresponds to tests where a single fastening assembly is fixed to one sleeper or
other rail support.
8.2 Preparation for test
The tests are performed using a set of fastenings fixed to a short length of rail fixed to one rail seat using the
fastening components as assembled in track.
8.3 Clamping force and uplift stiffness
Perform the test as described in ISO 22074-7.
The clamping force, P , shall be reported as the mean result of the second and third loading sequence during
a series of three loading sequences.
The uplift stiffness shall be reported as the mean result of the second and third loading sequence during a
series of three loading sequences.
The clamping force and the uplift stiffness are required for the calculation of the test loads described in
Annex B.
8.4 Longitudinal rail restraint
Perform the test as described in ISO 22074-2.
The longitudinal rail restraint, F, shall be reported as the maximum axial load on the rail without non-elastic
displacement occurring, as mean results of the second, third and fourth loading sequence.
The longitudinal rail restraint is not required for the calculation of the test loads described in Annex B.
8.5 Vertical stiffness
Perform the test as described in ISO 22074-8:2022, Clause 7.
Prior to performing the test, define the following values:
— the lower limit of force for determining the static stiffness, F ;
SA1
— the reference force for measurement of static stiffness, F .
SA max
Unless otherwise specified, 1 kN shall apply for F and 62,5 kN shall apply for F .
SA1 SA max
The vertical static stiffness of the fastening assembly, k , is required for the calculation of the test loads
SA
described in Annex B.
8.6 Lateral stiffness
Perform the test as described in Annex A.

The lateral stiffness of the fastening assembly, k , shall be reported as the stiffness calculated by dividing
LA
the lateral load on the rail foot by the average displacement of two measuring points lateral on the rail foot.
The lateral stiffness of the fastening assembly is required for the calculation of the test loads described in
Annex B.
8.7 Calculation of test loads and test loading angles
The calculation method of test loads and test loading angles is described in Annex B. This calculation method
requires clamping force and uplift stiffness (8.3), vertical static stiffness (8.5) and lateral stiffness (8.6).
Other parameters required are provided by the purchaser or manufacturer considering the railway track
and the vehicle conditions as designed.
Optionally, purchaser and manufacturer specify the test loads and the test loading angles without making
use of Annex B.
The test loads and the test loading angles shall be reported separately as “A load” and “B load” conditions.
8.8 Two directional static load test
8.8.1 Preparation for the static load test
Set up the test arrangement as shown in Figure 3 by using the modified test rail, the rail support (sleeper or
other rail support) and the fastening system components as assembled in track.
The load application strut shall have a width parallel to the longitudinal axis of the rail of not less than
90 mm to prevent the rotation of test rail in a plane parallel to the base of the rail.
The displacement of the test rail shall be measured at four points on the rail foot for vertical displacement
and two points on the rail head and two points on the rail foot for lateral displacement as shown in Figure 4.
The measuring points of vertical displacement shall be located on either side of the rail foot equidistant
from the loading point to each other in the longitudinal direction of the rail.
A pair of actuators shall be set according to the calculated or specified loading angles as shown in Figure 5.
Apply strain gauges on both rail clips if required by the purchaser.

Key
1 load application heads attached to actuators
2 modified test rail
3 sleeper or other rail support
4 rail clip
Figure 3 — Test setup
Key
1 modified test rail
2 measuring points of lateral displacement of rail head in field side or gauge side
3 measuring points of lateral displacement of rail foot in field side or gauge side
4 measuring points of vertical displacement of rail
5 loading points on the test rail in gauge side
6 loading points on the test rail in field side
Figure 4 — Displacement measuring points

a) Modified rail head and shortened rail web b)  Partially removed rail web
Key
1 height of loading position for test rail, h
T
2 eccentricity of loading position from rail centre, e
T
3 test loading angle applied from gauge side, θ
A
4 test loading angle applied from field side, θ
B
5 line of load application from gauge side
6 line of load application from field side
7 centre of gauge corn
...