RSSB
INS & RST Delivery Unit
TITLE: BASIS OF THE 1.44KPA CRITERION FOR THE TRAIN PASSING
PRESSURE PULSE
1.
Reason for this note
This topic concerns the pressure pulse produced by one train on another being
passed on an adjacent line. There has been uncertainty expressed regarding
the origin of the requirements in standards.
3.4
m
X
min X
2.
Background
In the diagram above, the train on the left is considered as moving, that on the
right is stationary. The passing pressure change generate by the moving train is
measured on the stationary train. Pressures are now usually measured at the
minimum gap between the trains and at mid-window height, (shown as red
dots).
GB passing train pressures are limited in Railway Group Standard GM/RT2100,
Issue 4, “Requirements for Railway Vehicle Structures”, (December 2010). The
requirement is:
Trains, with a maximum speed of greater than 80 mile/h, shall not generate a
peak to peak pressure pulse from any part of the train, (including nose to nose
connections), greater than 1.44kPa, (measured in the open air on a calm day at
height of maximum body width on the side of a stationary train on a straight
stretch of adjacent track).
Although not stated above, it has been established that the track spacing shall
be the GB standard value of 3.4 m, (or a correction applied for actual track
spacing to standard track spacing).
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INS & RST Delivery Unit
3.
Origin of the requirement
Although studies of this phenomenon had been undertaken for research and
development purposes during the 1970s, a need to quantify the magnitude of
the effect for existing and future high speed service routes arose in the late
1980s due to adverse comments from train users. The comments were
relatively rare, but mainly centred around passengers being startled by the
banging of doors, (particularly of external sliding doors used on some types of
multiple unit), and windows (particularly hopper windows), when passed by
other trains at high speeds. In addition, coffee and other drinks resting on tables
on the side adjacent to the Fast line, mainly in other HSTs, were regularly spilt
by passing HSTs. This was caused by a rapid displacement of the coach wall
against which the tables rested.
Although the events could not be called serious, it was evident that a criterion
was needed for the design of new trains for the:
i)
Door and window mounts and for the structural side-wall stiffness of
vehicles likely to be operating on high speed routes
ii)
Future high speed train nose shapes, (as it was known that it was the
aerodynamic shaping, as well as speed, of the source train that sized the pulse
magnitude).
Subsequently, tests were undertaken by the Research Division of BRB in 1988
to assess the magnitude of the largest pressure pulses produced by service
trains at that time. Tests were undertaken on ECML with a test vehicle being
passed, during both static and moving tests, by a number of service trains. Of
particular interest was the HST, as it was often the offending train and was
operating at speeds up to 125 mi/h on tracks at a nominal spacing of 3.4 m. In
some places, track spacing was known to be less than this and, of course,
considerably more than this in other places.
In addition, the Class 91 loco was being produced and it was necessary to
choose a criterion, bearing in mind future operation of the IC225 train (also on
ECML). In that event, it was decided during discussions between the senior
managements of the Research Division and the IC225 Project Team that IC225
operation at 225 km/h should form the limiting condition for defining the pulse
limit. At that time, prior to tests being undertaken with Class 91, it had been
assumed that the pressure pulse characteristics generated by the nose shape
of the Class 91 would be similar to HST, and therefore that a criterion based on
an HST result scaled up from 125 mi/h to 225 km/h should be adopted.
Results from the tests produced a mean value, (taken over several passes at
different track spacings and speeds of both trains), for the HST normalised to
3.4 m nominal track interval, which was given by the non-dimensional
parameter, CP = 0.6. At 225 km/h, this equated to a 1.44 kPa peak-to-peak
pressure amplitude.
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INS & RST Delivery Unit
Subsequent tests with IC225 showed the Class 91 to have slightly better
characteristics than HST, but the 1.44 kPa value was adopted for future project
design purposes.
Further, BR Research advised that, for practical purposes during track tests,
compliance with the criterion was to be checked against a measurement taken
at mid—window height on a stationary observing train on straight track on a
windless day. The result then was to be corrected to nominal 3.4 m track
spacing.
4.
Observations
In the same way as for the original tests and for the nominal service condition
chosen by Research and DM&EE management, there will be circumstances
now when 1.44 kPa is exceeded. For example, movement of the observing
train, the presence of cross-winds, reduced track spacing and track curvature
can all increase the pulse amplitude. Thus, it is important to adopt this
specification of the reference set of conditions under which the criterion is to be
met.
Note that the above implies that rolling stock operating on high speed routes
should be structurally designed to a criterion in excess of l.44 kPa for the train
passing pressure pulse case. For the proof load case of unsealed trains, this
will usually be covered by the +2.5 kPa specification for vehicle body structures
(see GM/RT2100). Sealed trains will be covered by their own more stringent
limits. However, fatigue load cases particularly for unsealed trains may need to
incorporate higher values associated with regular exceedances of 1.44 kPa.
Although the origin of the requirement appears rather trivial, as stated above the
more important need for such a requirement is to limit pressures applied to
other trains and structures passed by trains. As such there are requirements in
EN14067-41 and in TSIs to limit train passing pressures. The primary concern of
European railways is to ensure that trackside structures do not experience
fatigue damage from the cumulative effects of cyclic pressure loads caused by
passing trains. DB has reported such damage to wind and acoustic barriers
placed at trackside.
5.
Acknowledgement
The above note is extensively based on a separate note prepared by Roger
Gawthorpe and thanks are given to him for the information.
Terry Johnson
Aerodynamics Engineer
1
‘Railway applications – Aerodynamics – Part 4: Requirements and test procedures for
aerodynamics on open track’, EN14067-4.
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