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Dennis Storzek <destorzek@...>
--- In STMFC@..., "laramielarry" <ostresh@...> wrote:
A brief history of the Z bar eave. All off the top of my head; anyone
who needs dates will have to research them himself.
In the beginning... House cars were framed like houses. The roof
carlines mounted to the top of the side plates, and the roof sheathing
overhung the side, where it was finished with a rather prominent
fascia, wich served to divert the water past the top of the side
sheathing. This continued when car frames went from wood to steel, as
the roof was usually still a wood sheathed affair, covered with thin
This overhanging fascia tended to make the eaves the widest part of
the carbody, and the tables in the ORER were set up to reflect this,
giving a single set of dimensions that located the corner of the roof.
With the advent of solid steel roofs, where the panels were a
structural part of the roof, this overhanging eave construction became
unnecessarily complex. Someone hit upon a very elegant solution;
replace the steel angle top plate of the side framing with a Z section
laying on its side. The lower flange now lapped over the side, doing a
nice job of shedding water away from the side construction, while the
roof panels could be fastened to the upward facing flange. Since the Z
bar was solid piece, it didn't leak, even though the roof no longer
overhung the side construction. The ARA thought this was such a
significant improvement that they purchased the rights to the design,
and made it available to their membership royalty free.
This construction can be (and was) used on any steel framed car, be it
double sheathed, singled sheathed, or steel sheathed, so that fact
that a car has "Z bar eave" construction can't answer that question.
The widespread adoption of Z bar eave construction presented the
publishers of the ORER with a problem, however. There were now two
corners at the top of the side where before there was only one. Since
the clearance diagram angles in at the upper corners, either one of
these corners had the potential to hit something, so both needed to be
dimensioned, especially after railroads and carbuilders pushed the
roof up the couple inches the notch in the corners made possible, so
the dual dimensions were included in the ORER, to more accurately
describe the clearances required to accommodate the car.