Re: Howe & Pratt truss boxcars


Tom Gloger
 

Richard Stallworth wrote:
Can somebody tell me the differences between Howe and Pratt truss
boxcars?
then John Nehrich <nehrij@rpi.edu> wrote:
Richard - A Howe has the diagonals pointing to the bottom of the
door, the Pratt has them pointing to the top. I think of a hammock,
a sort of "V" shape, where the fabric is in tension, for a Howe. A
Pratt is like the cross section of a sawhorse, like an "A". The legs
are in compression. On a box car (or bridge) there are times the
members have their stresses reversed, and a box car has to also
withstand bulging pressures.
At one time, I used to classify single-sheathed box cars as "M"
or "W" for the orientation of the diagonals, but then found that not
everyone saw the letters the same way, and their "M" was my "W".
So let me see if I got this right:

If you were to continue the diagonal lines of a PRATT truss, the
lines from each side would meet above the car. The beams would
form an A shape, like the A in PRATT.

If you were to continue the diagonal lines of a HOWE truss, the
lines from each side would meet below the car. (And "Howe" would
the beams ever meet, below ground like that?)

If I got that memory device backward, please let me know quickly!

- Tom "Spring ahead, Fall back" Gloger


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