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TITLE: NOTE ON LIMITS ON AERODYNAMIC LOADS ON VEHICLES IN
TUNNELS
1.
Reasons for this note
At the GB Aerodynamics WG on 15th October 2014, it was concluded
that summaries of current requirements in the TSIs, Railway Group
Standards, and European standards regarding aerodynamic loads on
railway vehicles travelling through tunnels, would be useful. Of specific
interest is the potential for fatigue of railway vehicle structures resulting
from tunnel aerodynamic loads. This note gives a brief overview of the
requirements.
2.
Requirements in the TSIs coming into force in 2015
The CR INF and CR LOC&PAS TSIs come into force in January 2015.
There are no requirements relating to aerodynamic pressure loads
generated by trains travelling through tunnels.
Tunnels and trains are designed to ensure that passengers are not
exposed to a pressure change more than 10 kPa during the passage of
the train through the tunnel, under the assumption that there is no
attenuation of tunnel pressures through the train structure. The 10 kPa
limit is a medical health limit to mitigate the risk of damage to the
hearing of people on the train.
3.
Requirements in Railway Group Standards
There are several relevant references to aerodynamic loading of trains
in tunnels in Railway Group Standard GM/RT2100, which in issue 5 has
drawn together a number of requirements which were in different
standards previously.
GM/RT2100 Requirements for Rail Vehicle Structures
The following train structure components (among others) have to be
assessed for satisfactory performance when subjected to aerodynamic
loads in operation:
windscreens and windows, doors and gangways, canopies, fairings
or other mouldings attached to the bodyshell, equipment cases,
access hatches and panels, underframe skirts and coupler hatches.
For vehicles with maximum speeds of 125 mph or less, quasi-static
aerodynamic loads are covered by a requirement that all structural
elements or items of equipment attached to a vehicle have to resist, as
a proof load case, a uniform pressure load of 2.5 kPa without damage
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or significant permanent deformation. This load is considered to act
independently on either external or internal surfaces.
For vehicles designed to operate at speeds over 125 mph, or where the
vehicles are pressure sealed, an assessment of applicable quasi-static
aerodynamic pressure loads has to be undertaken and an equivalent
quasi-static pressure load derived. No methods to do this are provided.
The capability to withstand the quasi-static aerodynamic loads can be
demonstrated by testing, calculation, comparison with other vehicles, or
by a combination of these.
For transient aerodynamic pressure loads, there are also requirements
for vehicles with maximum speeds below 125 mph and for trains
designed for higher speeds.
For the former vehicles the capability to withstand the maximum
pressure loads, including the transient pressure loads, caused by a train
entering, passing through and exiting tunnels, has to be demonstrated
by testing, calculation, comparison with other vehicles, or by a
combination of these.
When determining transient pressure loads for vehicles with a
maximum speed in excess of 125 mph, any assessment has to include,
but is not limited to, the aerodynamic effects due to:
a) Train and formation length.
b) Train cross-section.
c) Leading and trailing end shape.
d) Tunnel cross section, including effects due to portal geometry on
entry and exit.
e) Tunnel length.
f) Ventilation shafts or cross-passages.
g) Single and double track tunnels.
h) Other train types likely to be encountered.
i) Relative entry times of trains entering a tunnel.
j) Operational speeds.
When determining the magnitude of transient loads, the degree of
pressure sealing of the vehicle has to be taken into account.
For vehicles with a maximum speed over 125 mph the effect of
aerodynamic transient pressure loads has to be included in the fatigue
life assessment of the vehicle and its components. Any operational
limitations or restrictions to limit aerodynamic transient pressure loads
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caused by these vehicles when operating alongside existing lower
speed rolling stock have to be identified.
4.
Requirements in European standards
There are only two relevant standards with relevant requirements, as
follows.
BS EN 12663-1:2010 Railway applications - Structural requirements of
railway vehicle bodies - Part 1: Locomotives and passenger rolling
stack
This standard only contains general requirements as follows:
“6.6.5 Aerodynamic loading
Significant aerodynamic loads arise in the following circumstances:
a) trains passing at high speed;
b) tunnel operations;
c) exposure to high cross winds.
The relevance of such loads shall be considered and a suitable
representation of the effects for analysis purposes shall be developed if
necessary.”
BS EN 14067-5:2006+A1:2010 Railway applications - Aerodynamics Part 5: Requirements and test procedures for aerodynamics in tunnels
In Section 5 and 6 of this standard, general descriptions are given of
how pressure loads are generated across the structures of unsealed
and sealed railway vehicles. Train lifetime estimates of tunnel crossings
are proposed. Also described are the way in which different amplitude
pressure loadings can be calculated for a given pressure time history
for a particular tunnel crossing scenario. In general, the information
provided is descriptive.
Revision of EN14067-5
This standard is under revision and Sections 5 and 6 will be rewritten to
include the methods determined from the AeroTRAIN Project. The
details of how these will be incorporated into the standard are not yet
clear. However, during the AeroTRAIN Project, a software tool was
developed which analyses a set of tunnels on a route and forms
pressure load collectives for trains using the route. It is likely that some
sort of load collective will be determined for a ‘typical’ European railway
route, which can then be used to characterise the potential fatigue loads
which should be sustained during the lifetime of a train.
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