TM 55-203
CHAPTER 5
UNDERFRAME ASSEMBLY
Section I. GENERAL
underframe over the car trucks through which the weight
5-1. Underframe Sills
of the underframe, super-structure (if any), and the
lading of the car carried by the longitudinal sills is
a. Center Sill. The center sill of a structural frame is
transmitted to the truck. The body bolster carries and
the built-up central, longitudinal structural member of
transmits its load through the mated body bolster and
the underframe of a car and forms the backbone of the
truck bolster center plates, the body bolster resting on
underframe. It transmits the buffing shocks from one
the truck bolster. A typical welded-steel underframe is
end to the other. It contains the couplers and draft
shown in figure 5-1
gears in pockets at either end.
5-3. Crossbearers and Crossties
b. Side Sill. The underframe side sill is the outside
longitudinal member of the underframe. In some cars,
Crossbearers are transverse structural members of the
especially flatcars, the side sills are strengthened. In
underframe placed between the bolsters. They act as a
other cars, such as gondolas and copper cars for
tie between the body side sills and the center sill
example, the entire side of the car may be designed as
anchorage and help to distribute the weight of the car
a deep plate girder or truss to carry much of the load to
and lading and to stiffen the structure. Crossbearers
the bolster. On hook-and-link equipped cars, it is
built as single units extend across the car from side sill
reinforced to withstand buffer shocks.
to side sill, usually with a filler between the center sills.
The term crosstie is commonly applied only to those
c. End Sill. The end sill of an underframe is the
members which tie together the side sill with the near-
tranverse member extending across the ends of the
side members of the center sill.
longitudinal center and side sills. This member may be
fabricated of rolled or pressed steel, with sill connections
5-4. Striking Plates or Castings
of either a bracket or gusset-plate type.
The striking plates or castings are a component part of
d. Floor Stringer. In steel car construction, the term
the coupler and draft gear arrangement. They are
floor stringer is applied to the longitudinal members
riveted or welded to the end sills and fitted around the
sometimes used to support floors. Longitudinal floor
opening for freight car couplers. They help prevent
stringers sometimes occupy positions similar to
damage to the center sill, as the coupler horn will strike
intermediate sills, but are not designed to act as sills.
when the draft gear is weak or defective.
5-2. Underframe Body Bolster
The body bolster is the transverse member of the
5-1
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