Re: from 40' 6' to 50' 6" box cars

Anthony Thompson <thompson@...>

AL Kresse wrote:
I agree on the Lt Wt issue. They experimented with 0.075" thk HSLA steels just prior to the war and then re-upped the ga. again. HSLA (then called high tensile) steel was used in side-sheets but at the older std thicknesses.
This is a subtle point. The stronger steel is no STIFFER, so making it thinner makes it prone to buckling, and that's what happened to some box cars with thinner side sheets: wrinkling, etc. This can be solved by adding intermediate posts between the regular side posts (that's the so-called "Alternate Center Riveting" or ACR box car design), but then the weight of the extra posts offsets the weight saving of the thinner steel.
This emphasizes that much of structural design, including box cars, is based on stiffness and not on strength. The best illustration of that is the dreadnaught end. It is trivially STRONGER than a flat end, but greatly STIFFER. The same goes for underframes, sides and roofs.

Anthony Thompson
Dept. of Materials Science & Engineering
University of California, Berkeley

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