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

Sarunac and Zeolla 91
STRUCTURAL STRENGTH OVERVIEW
As the LFE concept has been popular in Europe exclusively, the structural characteristics and
crashworthiness of the LFE need to be reviewed thoroughly to account for the differing design
philosophies between Europe and North America. In North America, traditionally a 2-g load
(two times vehicle ready-to-run weight) has been required, in some cases by law (California
CPUC).
In Europe, the compression strength is typically specified according to the vehicle type,
category, or rail service and not necessarily according to the tare or ready-to-run weight only.
For instance, in Europe, the typical compression strength of an LFE LRV is in the range of
40,000-100,000 lbs; however, the requirements for North American LRVs are in the range of
140,000-200,000 lbs. Caution must be used when comparing requirements for European LRVs
with their North American counterparts, particularly for structures and crashworthiness, because
the operating speeds in North America tend to be higher, even though the classification or label
of “LRV” is used in both regions.
CRASHWORTHINESS—STANDARDS AND INDUSTRY PRACTICE
In the past, the crashworthiness of LRVs was mostly defined by their buff load. A high buff load
was seen as the most straightforward path to ensuring that the vehicle structure did not suffer
large-scale collapse in collision, hence providing protection to passengers. Traditionally a 2-g
buff load has been required for LRVs in locations such as Baltimore, Maryland; San Francisco,
Santa Clara, San Diego, and Los Angeles, California; Denver, Colorado; St. Louis, Missouri;
Pittsburgh, Pennsylvania; and Boston, Massachusetts. The exception is New Jersey, where 1.0 to
1.1 g was specified. The Parsons Brinckerhoff study for NJ Transit’s LRV revealed that the
working team could not determine the technical rationale behind the 2-g buff load. The 1-g
requirement could not be explained convincingly either. Furthermore, specifying a minimum
buff load does not necessarily limit the peak loads and accelerations experienced during a
collision because the collapse load of the structure is often higher than the static buff load.
Today, the industry is considering an alternative approach. The strength-based
crashworthiness approach is augmented with energy-based crashworthiness requirements; the
ultimate goal is to reduce passenger deceleration rates during a collision while controlling the
absorption of collision energy to minimize loss of space in the occupied volume of the vehicle.
The strength-based philosophy is currently the most widely used approach to ensure some
level of rail vehicle crashworthiness. Under this approach, vehicle specifications typically limit
the various strength requirements of the structure. The most significant strength requirement is
the buff strength. Ultimately, the strength requirement does not consider the energy-absorbing
capability of the vehicle structure. If the structure were designed not to crush by utilizing very
high strength, then the load and decelerations would also reach very high values during an
accident. Depending on the design, collision energy might be dissipated as fracture, derailment,
or override—all of which are generally uncontrolled and undesirable outcomes.
The energy-based crashworthiness (or CEM) philosophy is based on providing protection
against one or more specific collision scenarios. These scenarios are used to determine, by
considering the physics of collisions, an estimate of the energy that must be absorbed and the
structural components that must be used to absorb the energy. Selection of specific collision