Rolling Stock Crashworthiness
in the Modern Age
Dr Jademond KiangSenior Consultant, Specialist Engineering, Australia
Rolling stock Crashworthiness in the Modern AgeRail
In the context of passenger rolling stock body shell
structures, Australian crashworthiness design
requirements and standards (and standards from
around the world) provide a good design basis for
achieving inherently crashworthy designs. However,
they do not necessarily cover some commonly
occurring scenarios applicable to the Australian rail
environment. For the scenarios that they do cover,
the design criteria do not necessarily reflect the
severity seen in practice.
In the Australian rail environment, which has level
crossings in regional areas along with increasing
popularity of mixed traffic light rail systems in urban
areas, the risk of impact by road vehicles onto the
side of rolling stock is elevating in recent times. This
raises the question of whether designing rolling stock
to meet the requirements of crashworthiness
standards alone can be considered sufficient due
diligence. Or would further due diligence be
warranted?
What is crashworthiness?
Crashworthiness can be described as how well a
piece of rolling stock performs in terms of its ability to
mitigate severity of consequences in a collision in a
controlled manner, and how well the passengers are
protected during such an event.
During a train collision, an enormous amount of
energy is involved. The forces involved would be in
the order or mega-Newtons and the energy levels
involved would be in the order of mega-Joules. Such
high levels of collision energy and forces need to be
managed appropriately in order to provide
Rolling Stock Crashworthiness
in the Modern Age
Rollingstock collisions are few and far in between. In the modern age, train protection systems in the rail
network are deployed to prevent trains from colliding. However, when a train crash does occur, the
consequences can potentially be catastrophic due to the magnitudes of energy involved, says Dr Jademond
Kiang, Senior Consultant – Specialist Engineering, SNC-Lavalin Atkins Australia.
passengers with a better chance of survival should
a collision is to occur.
Crashworthiness standards
There are various local and international standards
in relation to whole-consist crashworthiness
requirements. One of the most notable and
prevalent standard today is the European Standard
EN15227.
Examples of other international crashworthiness
standards from various regions around the world
are listed in Table 1 below:
Table 1 –Crashworthiness Standards from various
regions
The RISSB standard AS7520.3 applies to the
Australian rail industry. However, this standard
references EN15227 for crashworthiness
requirements for frontal crash requirements.
One notable requirement of EN15227 is that full
train-on-train head-on collision is required to be
assessed, which can involve impact speeds of up
to 36km/h depending on the type of rolling stock.
However for light rail vehicles, the impact speed for
crashworthiness assessment is only 15km/h.
Country of Origin Standard
UK, Europe, parts of Asia EN15227 [2]
Australia AS/RISSB7520.3 [3]
USA FRA 2010 [5]
NZ M3000 [4]
These standards almost exclusively address
frontal collision scenarios without regard to other
collision scenarios such as side-on impacts on
rolling stock.
Side impacts are not uncommon in the Australian
rail environment due to popularity prevalence of
level crossings in regional areas and mixed traffic
conditions in urban light rail systems.
Lateral inward strength of the side of the carbody
at sole bar and waist rail levels are considered by
AS7520.3, which are 180kN and 30kN static
loads respectively. However these loads are
intended to address rollover rather than side-on
impact.
Australian train crash statistics
A CRC research report [1] has summarised train
incident statistics over the period 1997-2010
published by the Australian Transport Safety
Bureau (ATSB). Some pertinent statistics
relevant for this discussion are:
1. On average, head-on collision speeds are
higher than defined in EN15227;
2. 62% of incidents involved kinetic energy of
less than 212MJ;
3. Majority of incidents were less than 40MJ ;
4. Kinetic energy of 220MJ was involved (on
average) for impacts between 0° and 45° on
the structure.
Rolling stock Crashworthiness in the Modern AgeRail
These statistics infer that the majority of incidents
(or on average) in Australia for the period 1997-
2010 involve speeds higher than crashworthiness
design speeds. Statistics for side-on impacts are not
available for discussion in this paper. However side-
on impacts are generally expected to be detrimental
to passenger survivability as the side walls of rail
vehicles inherently do not have sufficient space to
house energy-absorbing crumple zones.
According to these statistics, the majority of rail
incidents involve less than 40MJ of energy. For a
typical double decker passenger train, this
magnitude of energy translates to an incidentce
speed of approximately 48km/h. For a metro
train, this translates to 76km/h.
The maximum head-on impact scenario for
crashworthiness design in EN15227 is 36km/h.
With metro systems and light rail networks,
impact speed for crashworthiness design
reduces down to 25km/h and 15km/h
respectively.
In addition, average non head-on frontal impacts
(between 0° to 45°) involve a kinetic energy
magnitude of 220MJ. This translates to over
100km/h for typical heavy rail passenger vehicle
in Australia.
Figure 1 – Waterfall train disaster
Rolling stock Crashworthiness in the Modern AgeRail
As discussed previously, side-on impacts on rolling
stock are not directly addressed in EN15227 or
AS7520.3, not even for mixed traffic environments
such urban light rail vehicles.
It is up to the individual owners, purchasers or
operators to exercise voluntary due diligence to
mitigate risks associated with side-on impacts or
any other collision scenarios not covered by the
design standards. This often involves undertaking
engineering investigation by first-principles involving
FEA or physical testing.
Engineering assessment of crash
scenarios
Regardless of mandatory or voluntary nature of the
crashworthiness requirements, they need to be
assessed by sound engineering methodologies.
One way to address modern crashworthiness
requirements is by physical testing of various
designs and/or modifications in an effort to assess
or determine the most appropriate design.
Another way to address crashworthiness
considerations is by virtual crash testing. In other
words, crashing trains in a computer by undertaking
FEA to assess structural performance.
Method 1 - Physical Crash Testing
The most direct method of verifying crashworthiness
performance is physical testing of the car body
structure or sub-components of the structure. Whilst
physical testing can theoretically be done, it has a
lot of undesirable attributes in practice. These
include:
• Monetary cost associated with the preparation of
the full-scale test article;
• Monetary cost in relation to test facility;
• Long timeframe between test cycles leading to
an inefficient design process;
• Variance between as-built test specimen and
actual production article leading to test results
not reflective of actual performance;
• Safety risks associated with large collision
energy magnitudes (in the order of mega-
Joules);
• OH&S and insurance complications associated
with full-scale physical testing.
Method 2 - Virtual Crash Testing
A lot of the undesirable attributes associated with
full-scale physical crash tests would no longer be
applicable if the process is performed virtually:
• Cost of preparing test articles and facility (FEA
models) will be significantly reduced;
• Timeframe between ‘test’ cycles will be
significantly compressed;
• No OH&S and insurance complications;
• And most important of all, there would be no
safety risks.
Mathematical Theory of Virtual Crash Testing
As described earlier, virtual crash testing involves
the use of FEA technology. This section provides a
high level summary of the mathematics behind the
finite element method.
Crash scenarios are dynamic events. Therefore, the
effects of mass, stiffness, inertia, acceleration/
deceleration, velocity and damping all need to be
taken into consideration.
In a dynamic system, the system of differential
equation is as follows:
[m]{a}+[c]{v}+[k]{x}={F} (1)
where:
[m] is the mass matrix;
{a} is the acceleration vector;
[c] is the damping matrix;
{v} is the velocity vector.
For crashworthiness work, the differential equation
is solved by re-arranging it into the following format
and solving for acceleration directly (damping is
removed for simplicity of discussion):
{a}=[m]-1({F}-[k]{x}) (2)
This is often referred to as ‘explicit’ FEA because all
quantities on the right-hand-side of the equation are
explicitly known.
Rolling stock Crashworthiness in the Modern AgeRail
Assessing impact scenarios not covered by
design standards
As aforementioned, one pertinent crash scenario not
covered by design standards is side-on impact.
To demonstrate the consequence of a side-on
impact, the scenario is simulated for a typical metro
rail car using explicit FEA software LS-Dyna. The
model setup is shown in Figure 2.
The objective of this assessment is to investigate the
difference in response from the various impact
masses and speeds that are conceivable in the
Australian rail environment.
Structural response of the system (such as velocity,
acceleration, stress and strain distributions) can
then be calculated from the acceleration vector at
each time step.
The type of effects the explicit scheme can capture
efficiently include (but not limited to) the following:
• Large plastic strains and geometry changes;
• Post-yield and material fracture;
• Stress wave propagation;
• Pre and post buckling response;
• Surface-to-surface contact and associated
friction.
Further technical details relating to the finite element
method can readily be found in FEA literature such
as [6-10].
The explicit FEA scheme is a widely accepted
method of virtually assessing train crash scenarios
reliably and accurately. This method is widely used
to design and optimise rolling stock fleets in detail
before production of the first physical prototype. For
this reason, this process is sometimes referred to as
virtual prototyping.
Assessing impact speeds higher than
stipulated in design standards
It may be impractical to mandate head-on crash
scenarios at higher impacts speeds than currently
stipulated in the standards.
Crash energy (kinetic energy) is proportional to the
square of the impact speed a shown in Equation (3)
below.
Kinetic energy (KE) is calculated as follows:
KE=mv2/2 (3)
In the rolling stock consulting environment, there are
occasional requests from clients to assess head-on
collisions at higher speeds (approximately 30km/h
compared to 25km/h stipulated in EN15227). The
impact energy increases by a sizeable 44% from
the design requirement for a 5km/h increase in
impact speed (refer to Equation (3)).
Therefore, designing a structural system to
accommodate higher impact energies associated
with small increases in impact speed may render
the structure uneconomical to manufacture and
operate.
Figure 2 – Impact of truck analogue into side
of a typical metro rail car
In this assessment, 20t and 40t truck analogues
impact the side of a typical metro rail car. The truck
has a frontal footprint of 2.6m by 3.5m.
ScenarioMass
(t)
Impact
speed
(km/h)
Kinetic
Energy
(MJ)
1 (semi) 20 25 0.48
2 (road train) 40 25 0.96
3 (road train) 40 50 3.80
Table 2 – Truck impact speeds and
associated kinetic energy
The impact energy is linearly proportional to the
mass of the truck and proportional to the square of
the impact speed (refer Equation (3)). Therefore,
increasing the impacting mass from 20t to 40t
doubles the kinetic energy of the impact whilst
increasing the impact speed from 25km/h to 50km/h
(same mass) results in a four-fold increase in
energy.
The results of the various collision scenarios are
shown in Figure 3 through Figure 5.
Rolling stock Crashworthiness in the Modern AgeRail
Under Scenario 1 (which can be considered as a
moderately sized truck found in regional areas
impacting at a moderate speed), where the kinetic
energy is halved further, the intrusion of occupancy
space is significantly reduced, albeit not
insignificant.
As a comparison, the peak dynamic impact force
acting on the sidewall in Scenario 1 (obtained from
FEA) is over 1MN, which is well in excess of the
static loads stipulated by AS7520.3. The static
lateral inward loads defined in AS7520.3 are 180kN
and 30kN for sole bar and waistrail, respectively.
However, these lateral inward loads are intended for
rollover strength assessment rather than side-on
impact (there are no other load cases in AS7520.3
that address side wall lateral inward loads).
The dynamic impact forces are greater still for the
higher impact mass and speeds such as in Scenario
2 and 3.
It should be noted that these scenarios are not
meant to be photorealistic. Trucks, in reality, would
have their own crumple zones thus some of the
impact energy would be absorbed by plastic
deformation at the front of the trucks. The
simulations presented in this paper serve to
demonstrate the susceptibility of typical rail cars in a
conceivable side-on impact in the Australian rail
environment.
The simulation results presented also demonstrate
the discrepancy between the impact forces obtained
from dynamic simulations compared to the static
design loads stipulated by AS7520.3. The
discrepancy between simulation and design
standard widens further for more onerous impacts
such as that in Scenario 3.
Therefore, it may be necessary for rolling stock
designers to consider the side-on impact scenario
as an out-of-standard requirement. Indeed, some
Australian light rail procurement projects in modern
times include the side-on impact scenario to be
assessed by dynamic simulation (explicit FEA).
In these out-of-standard assessments, the
acceptance criteria are usually set and agreed
between the supplier and purchaser rather than by
design standards.
Figure 3 – deformation from 20t truck
impacting at 25km/h
Figure 4 – deformation from 40t truck
impacting at 25km/h
The results illustrate that a typical metro rail car
would be deformed significantly under Scenario 3. It
is however unreasonable to expect a rail car to
accommodate the impact of a 40t truck (analogous
to a road train) travelling at 50km/h without significant
deformation.
If the same truck us travelling at half the speed
(Scenario 2), the kinetic energy is reduced by 75%.
Under this scenario, there is still significant intrusion
of occupancy space.
Figure 5 – deformation from 40t truck
impacting at 50km/h
Rolling stock Crashworthiness in the Modern AgeRail
Is the Australian rolling stock industry industry
enhance its awareness aware of to the risks
associated with rollingstock collisions by simply
following the design standards? Should these risks
be mitigated by considering the performance of
rollingstock in collision scenarios that are outside of
standard?
Dr Jademond Kiang is the Senior Consultant – Specialist
Engineering at SNC-Lavalin’s Atkins business, now one of
the world’s largest consultancies with more than 55,000
people employed globally of which 5,000 are specialist rail
consultants. We offer clients a complete end-to-end
range of services, unique breadth of capability, and a
resource base that enables us to deliver all scales of rail
projects globally. We combine traditional engineering with
the latest techniques to deliver safe, reliable and
sustainable outcomes, transforming rail networks and
shaping the future of transport.
Conclusions
The passenger rolling stock crashworthiness design
standard used in the Australian rail industry
(AS7520.3) is similar in scope and stringency to
those from other parts of the world. In fact the
crashworthiness requirements in AS7520.3
stipulates the use of European Standard EN15227,
which is a widely used and accepted international
standard.
However, these standards do not necessarily cover
all conceivable impact scenarios found in the
Australian rail environment. Some scenarios may be
indirectly addressed by simplified methods of
assessment such as static structural analysis.
As demonstrated in this paper, this simplification
may not necessarily reflect the realities of a dynamic
event that is a collision scenario.
Meeting the requirements of the design standards
alone do not guarantee a train that is crashworthy in
all conceivable circumstances.
However, following and meeting the requirements of
the standards would likely provide a solid foundation
and good design practice that will be engineered
into the rolling stock, thus increasing inherent
crashworthiness in out-of-standard crash scenarios.
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