Re: Pratt vs. Howe boxcar trusses


Andy Carlson
 

I think that the Howe truss designed car was familiar with the RR's back when cars were mostly of all wood construction. The engineering of wood trusses takes advantage of the greater strength of compression for wood- hence the Howe truss. Later, when steel underframes and SS cars became popular, basic familiarity with Howe trusses caused a lot of steel framed boxcars to be built with the Howe truss with it's structural members in compression. As early engineering students quickly learn, steel is much stronger in tension, and bridge trusses take advantage of this property to keep the amount of steel used to the minimum. The enlightened RR engineering departments recognized this when the Pratt truss was selected with it's structural members taking advantage of steel's tensile strength. Not all RR engineering departments were so enlightened- hence the large numbers of Howe steel trussed cars being made.
-Andy Carlson
Ojai CA

Denny Anspach <danspach@...> wrote: Although I seem to know that in bridge engineering a Pratt truss is
inherently lighter than a Howe, and thus in practice, the Howe is
relatively rare, how does this play out in boxcar design? Does the
engineering of the door openings, or the weight and strength of the
underframe have something to do with it?

Denny
--
Denny S. Anspach, MD
Okoboji, Iowa

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