b. The side sills are outside longitudinal members running the entire length of the car, one on each side.
They are constructed so that a channel is formed by two flanges that extend toward the inside of the car and
have a flat surface on the outside. The cross-members, discussed in subsequent paragraphs, fit into the channel
of the side frames. On some cars, the side sills are thickened in the center to increase their strength, and, on
flatcars, stake pockets are cast, riveted, or welded on the flat, outside surface of the side sills.
c. The end sills are transverse members that extend across the ends of the longitudinal center and side sills,
one at each end of the car. They are channel beams with flanges and are considerably heavier than the side sills.
Angle bars and plates are riveted or welded to the end sills to connect them with the longitudinal members. An
opening in the center of each end sill provides access to the draft gear pockets in the center sill.
4.3. BODY BOLSTER
The next important parts of the underframe are the two body bolsters, the transverse or cross members of
the frame. In an earlier discussion of car trucks, it was pointed out that the truck bolster has a matching
counterpart that is a part of the car under-frame; this is the body bolster. As you probably remember, the truck
bolster has a center plate that matches and contacts the center plate of the body bolster. A center pin secures the
connection between the two plates, and the weight of the car and its lading is transmitted to the truck by the
contact and connection of these plates. Therefore, the body bolster must be a strong structural member of the
underframe because it is in the direct line of weight transmittal.
Body bolsters are located near each end of the underframe and are perpendicular and attached to the center
sill or backbone of the frame. Each consists of a center plate, top and bottom cover plates, and two side
bearings. The center plate has already been discussed. The top cover plate passes above the center sill, and the
bottom cover plate has the center plate and the two side bearings attached to it. Again, remember the truck
bolster side bearings that were discussed earlier (par. 3.3c). Their matching members are located on the bottom
of the body bolster, and together they prevent excessive sidesway of the car.