Thank you all for your generous informative replies! I had a suspicion it was weight reduction like on a plane superstructure.
If termites start eating steel, the world is in deep trouble! -Rob
ndbprr I doubt the removal of the steel on your car would amount to much weight savings.
Still, it seems to be a priority to remove excess weight for a variety of reasons:
https://www.railjournal.com/freight/rail-cargo-wagon-shows-new-modular-wagon-prototype/
It seems weight reduction is a "thing".
https://www.gwrr.co.uk/news/the-first-of-freightliners-new-ffa-g-wagons-arrive-in-the-uk/
ndbprr I believe those large ovals are for visibility for the fork lift operators to confirm they are loading or unliading the bundles in order.
I simply grabbed a centerbeam car as an example. There are others (the Gradall boom in Overmod's reply) or examples of excess weight reduction by removal of material without compromising integrity. The end bracing of cylindrical hoppers come to mind.
Good Luck, Ed
Here's a discussion with many additional pictures:
https://hotraincollector.com/unusual-all-door-boxcars/
Note in particular the 3/4 view of the side-sill construction; these cars had Hydra-Cushion center sill construction for load bearing, and comparable 'all-door' sliding-door cars for McCloud River later had conventional deep side sills without lightening holes.
Both Ed and Eda are correct.
The main reason is to reduce Tare Weight = Increase Loading Weight.
Secondly; Better access for easy minor maintenance.
David
To the world you are someone. To someone you are the world
I cannot afford the luxury of a negative thought
Termites
If the side sills are 1/4" thick (not saying they ARE), and one square foot, then the weight saved for the car is 260 pounds.
Other possible reasons:
'Cause it looks cool
'Cause it makes the designer look more "high tech" and "with it"
Better access
Easier visual inspection
Ed
Some background info. Car gross weight is based on the weight the trucks can carry and is expressed as weight per axle. I doubt many loads are so close to weight limits as to require removal of car weight but it does add that benefit. The lumber catrs shown require removal of wood bundles alternately from each side of the car or the car will tip over if one side only is removed. I believe those large ovals are for visibility for the fork lift operators to confirm they are loading or unliading the bundles in order. I doubt the removal of the steel on your car would amount to much weight savings. Steel is around 1100# per cubic foot. I doubt there is much more than that in volume of removed material but it is what it is.
Ed's right; they're lightening holes. All-door cars with roll-up doors the whole length require very stiff sill framing, both against sag at the outside of the frame and against racking/twisting, and the tare weight is measurably lessened by the holes.
Same principle as the telescoping boom on these:
https://live.staticflickr.com/2852/12731215894_79412a5337_c.jpg
Perhaps the same reason this one does?
Reduced tare weight = increased loading weight.
D-B_Wagon by Edmund, on Flickr
This is a Bachmann boxcar I restored. There's a row of holes along the bottom of each side. Anybody know what they were for? -Rob