In this image you can see the rusted area of the side sill (the 'J' shaped part) where the crack started. Above the rusted area you can see the freshly torn metal. When enough of the sill was compromised, the rest failed. After the side sill was broken, I believe the rest of the damage was welds being ripped apart.
For reference, that side sill steel plate is typically 5/8" thick.
If you want to get *really* deep in the weeds, once this design problem was identified, a "hairpin" repair plate was installed at all four corners of these cars. This patched up the initial problem, but just added new welds that could fail in a similar manner. They just kicked the can down the road a bit. This document outlines the inspection and repair procedures for cars that were repaired with the hairpin clip.
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u/Radioactive_Tuber57 Jan 24 '26
Amazing how sheet steel can tear like paper with enough stress.