Re: boxcar design evolution


Pieter Roos
 

It would seem that some 1920's cars were built with the USRA type pressed frame members, but many were not. PRR added reinforcing "boots" on the ends of the framing on many X26 USRA designed cars, and IIRC D&H and some others actually replaced the original framing with 'Z' section material during rebuilding. The WWII "War Emergency" designs also seem to have reverted to standard steel shapes. These events could suggest that the USRA type members were not wholly successful. At least by the 1940's it would appear that standard shapes had won out.

OTOH, hoppers and gondolas, both composite and all steel, continued to use more specialized shapes in their framing. The early PRR single sheathed designs (R7 and X23) also used special pressed members, so USRA was clearly not the first.

The USRA single sheathed design would appear to have been a step forward in height, as the 1920's ARA standard called for scaling the IH back by 6 inches, with the original USRA size as an option.

Pieter Roos
Connecticut

--- In STMFC@..., "soolinehistory" <destorzek@...> wrote:
<SNIP>
Where are you saying these fit in the evolutionary chain, Rob? The first steel frame boxcars used stock mill shapes, either Z, C, or L section, while some of the last single sheathed composite cars did likewise. The cars with the pressed framing fit in the middle, a good idea that came... and went.

The argument for purpose designed pressings is they make more efficient use of material, although I don't think the car designs that made use of them were appreciably lighter.

The argument against purpose designed pressings was that they were difficult to repair; the railroad would have to make custom pressing dies to make replacement parts, whereas mill shapes were available off the shelf, so to speak. Late in the cars lives it was found that the pressings trapped water and tended to rust out near the bottom, but I don't think this happened fast enough to really have any impact on the debate; the cars lasted through a reasonable service life without major problems. Anyway, cars with Z section framing also could have problems with cracking of the posts and braces due to repeated stress reversals in the truss members.

It appears that the two design philosophies coexisted for years without either proving to be truly superior.

Dennis

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