Massively subtle bridge SUPERstructure differences

Alright guys, I was trying to come up with a good title to this posting because, to be honest, only nerdy structural engineers will appreciate this posting. 

I just created a video that discusses the subtle differences in railroad flat cars with raised side sills. These same concepts can be applied to flush deck railcars but we just happen to have several raised side sill railcars sitting around.

Selecting the correct railcar style is very important and ensuring a good, matching pair is critical when building a bridge. 

I prefer the triple WT railcar styles as they tend to be in better condition and are less prone to defects. However, a double U railcar can be perfectly fine so long as it is in good condition. 

One common question I get is in regards to a WT beam. First of all, lets get some nomenclature straight. The term "I-beam" is a very generic term that really doesn't mean anything specific anymore. There are several types of "I-beams" out there, including:

  • S-beams: Although these are called "standard" I-beams, they are not really "standard" any more as the W-beams are by far more least in our world. They range in size from 3" tall to 24" tall. I have had to order these before and they can, technically, be ordered as an "Ibeam", such as a I12X50, which is the heaviest 12" tall beam normally made weighing 50 lbs per linear foot.
  • J-beams: I actually just made "J-beams" up because I have actually never had to order one of these "junior" beams. I honestly do not know what these little guys are technically called. They are the least used. They range in size from 5" tall to 12" tall so they are not very small but they tend to be very thin. For example, the heaviest Jbeam, the J12X11.8, is only 11.8 lbs per linear foot. That's pretty light as compared to the heaviest comparable Wbeam, the W12X336, which comes in at 336 lbs per linear foot which is more than 28 times heavier than the heaviest J12 beam. 
  • W-beams: These are the "new standard". They come readily available in a HUGE variety of sizes and are used by far the most. These are considered a "wide flange i-beam" but the common term used in most fabrication shops is just "i-beam". Usually, the verbiage is something like "hey, have any i-beams been delivered today because I am expecting a 40' stick of W6X16". The biggest wide flange i-beam we have used is a W44X335 which came in a 40' stick weighing 13,400 lbs. That's a big beam!

Alright, now lets focus on W-beams. If you take a W-beams and split it in two you will get two "T's". That's kind of hard to explain so just watch this video that I found on YouTube: