As suggested, "Hogging" "Hog backed" or "Hogged" are terms, used for wooden railroad cars (mostly flat cars, as the wall truss in box cars make them less susceptible) which have had their truss rods tightened too much.  As noted by others it comes from wooden ships, which would hog because the center of the hull was more buoyant than the ends.

Unlike modern flat semi trailers which are designed with a hog which flattens under load, a hogged railroad car was not desirable.  It generally was thought of as a worn out car, hogged as car inspectors tightened the truss rods as the wooden sills failed, and end beams crushed.  I suspect that a hogged car was more  likely to fail in train service, especially when unloaded, as the train bunched behind them.

I spent nearly 3 months researching how to tighten truss and tension rods for a restoration project.  I read every copy of National Car Builder, every issue of Railroad Gazette, every issue of Railroad Engineering, all the Master Car Builders proceedings, Voss and Kirkman.  There was nothing in writing about how tight a car's truss rods should be tightened, nothing on how to do it (do you jack and block the car straight or can you pull it straight by tightening the truss rods?)  I turned to wood truss bridges, particularly those being rebuilt in modern times with preservation studies... again nothing...  Apparently this was not how that knowledge was taught...  I did find information in interchange rules on how much a railroad could charge if they tightened truss rods or replaced a truss rod on the queen post if became unseated on an off road car,,,  The allowance for tightening as less than the minimum billable amount (but could be charged if other work was done).  resenting a truss rod was independently billable. 

Randy Hees