I currently have this issue, I have 2 railway tracks going down a hill that are mounted to a C-channel frame sitting in between a I-Beam. I need to lift the track by 12" as shown in red so I have to have a opening under the rails as shown in yellow. I would have to attach a new structure as shown in green I am not a structural engineer so could someone please give me some ideas. I'm guessing I cant just use 2 pieces of C-channel on each end since that would cause a moment load at the top of the new c-channel. I can mount new parts on the current I-beam or c-channel.
See picture attached.
I would be VERY concerned about any side loads leading to parallelogram type failure. You really should have an engineer that understands mechanical analysis look at this. You never mentioned the amount or type of loading.
This is a hill at about 35 deg incline, no turns just up and down. The load that is originally on the rails is a 2000lb rail car going up and down, the load would be the same, just shifted up by 12".
I would prefer to see heavy wall square or rectangular tubing. The symmetrical cross section creates even loading and stress. I would also include gusset plates where you can to stiffen the angular reactions.