TR Circular E-C058_9th LRT Conference_2003.pdf - Florida ...

124 Transportation Research Circular E-C058: 9th National Light Rail Transit Conference
Derailment Investigation Approach
The wheel to rail interface was exhaustively investigated, and complex mathematical models
were developed to simulate the behavior of the vehicle on measured Green Line track geometry
and irregularities. The aim of this investigation was to isolate the detailed mechanics of the
derailment, and to identify appropriate corrective action strategies.
Initial work focused on addressing the derailments using the simple Nadal theory as a
safety limit (Figure 2). This limit remains a conservative one; although, for an independent
wheel, more accurate approaches can be employed when full details of the wheel-to-rail interface
are available. Initial efforts were focused on increasing the Nadal limiting value by addressing
the most controllable variable—the effective flange angle. The original wheel profile design
employed a 63-degree flange angle, driven by the fact that all other vehicles on the Green Line
use such a profile. Analysis quickly showed that a change to a more modern 75° flange angle
was feasible and should deliver significant increases in the derailment safety margin by
increasing the Nadal limit. Considered simply, for a constant vertical load, the tolerable lateral
force between wheel and rail could be increased by 53% by changing the flange angle. In order
to confirm the validity of this premise, an extensive investigation was launched.
The conceptual approach followed during the investigation is shown in Figure 3. This
approach was followed to develop, refine, and validate an accurate dynamic model of the vehicle
Vertical Load – V
Nadal’s limit:
Lateral
Force – L
L
V
Tan δ − µ
=
1+
Tan δ
Where µ is the coefficient of friction
between wheel and rail
Effective Flange Angle δ
FIGURE 2 Nadal’s derailment theory.