SACS Model - I-Beam inside a Box Beam

Hi all

I have a loading scenario where an I-beam is put through two parallel box beams (not rigidly fixed or welded, just slid inside the box beam, to simplify for understanding) in a frame structure to act as a hang-off feature (the I-beam acts as "arms" to support the frame). This is my most critical load for the frame, as it is expected to support close to 450kips.

Does anyone have a good method to evaluate this situation? I have tried to combine member properties of the box beam and I-beam but it did not behave as I would expect. I have tried various other methods sharing nodes and overlapping beams but everything does not seem correct to do in the SACS world. I have around 7 years use with the program but mostly simple structural work and no complex loading scenarios as such.

Thank you