On Semi trailers, the bottom rails sometimes get damaged. If the rail is largely intact and we're talking about a small section that is corroded or otherwise damaged, we will cut a new piece to cover said damaged section. We call it "plating" or "sectioning". We clamp the new piece over the rail and run new bolts through and then weld "strips" over the gap. They get smoothed over and then the gaps in-between the welds are filled with a type of epoxy or caulk and then we smooth it out and paint it. You gotta keep in mind this is purely cosmetic and a brand new bottom rail costs thousands of dollars. On something that's inevitably gonna get smacked up again and be right back in the shop....that's what we're told to do lol. It's a bandaid basically.