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

Sarunac and Zeolla 97
to evaluate a specific design, but rather to compare vehicle design philosophies and how they
might influence the design loads for the LFE. In order to limit the number of permutations in the
analysis, the LFE buff strength was selected based on a reasonable maximum value given
consideration for weight limitations.
The weight for the LFE using CEM on the existing vehicle was estimated using the unit
weight of the existing vehicle: 1,100 lbs/ft. This value is assumed to include the weight from
structures added for the CEM zone. The unit weight estimate is somewhat conservative because
it includes the weight of subsystems, such as propulsion inverters, that will not be present on the
LFE. For this study, it has been assumed that the collapse strength of the LFE is equal to the buff
strength, which is a very conservative assumption. In reality, collapse strength or ultimate
strength is typically higher than the static buff strength.
Additionally, models with CEM zones require the maximum length of crush to be
specifically defined in order to properly simulate the difference between CEM and the passenger
compartment collapse. The following lengths were used:
• Crush zone length for Simulation 1 is 21 in. (this value was selected as a base point).
The zone is assumed to begin at the back of the anticlimber, extending 21 in. into the cab area.
• Crush zone length for Simulation 2 is 30 in., extending from the back of the
anticlimber inwards.
The springs that represent the passenger compartments and the LFE structure have been
modeled with sufficient length to capture the full dynamic response of the system; therefore, the
maximum crush can be estimated. In other words, a crush length was specified for CEM zones
only.
Generation of Characteristic Force Deflection Curve for the Vehicles
The individual structural characteristics and the crush zone lengths noted in the previous section
were combined in the models to represent the response of the structure under different collision
scenarios. The simulation depicts the response of the vehicle as a whole and of the separate
“cars” or modules (such as the leading car or LFE). To achieve this, the idealized forcedeflection
curves were generated using the strength characteristics. The curves represent the
average force generated as the coupler and structure collapse over distance. These curves are
idealized to simplify the calculation; they are estimations with sufficient accuracy for a
preliminary study. In reality, a rail car structure collapsing under dynamic loading displays
highly varying force deflection curves with many peaks, although an average level is typically
maintained.
The force versus deflection curves used in the simulations represent
• The existing vehicle, including the couplers;
• The end cars of a vehicle with CEM zones designed to 200,000 lbs buff strength;
• The end cars of a vehicle designed to a 2-g (based on total weight of end cars and the
LFE) buff strength;
• The LFE module designed to the 200,000 lbs buff strength; and
• The LFE designed to 2-g (based on total weight).