3d Printed Spiral Staircase Structural Simulation I am an artist (I also am a EE PE so not a complete ENGR idiot) who is building a spiral staircase using 3d printed concrete forms for the center spire with mortises where the steps (2" by 3" square steel tubing) will anchor to. I constructed my own giant 3d printer to print out concrete formwork and I have the forms ready.

I have designed everything in Fusion 360 because it allows for complex 3d models that would be hard to draft in software for structural engineering. I have performed a few static simulations to see if using 6-#4 rebar will be sufficient but I do not trust Fusion 360's simulations that much because fusion 360 is geared to mechanical engineering/machining applications and not the compressive loads of larger structures. 

What structural simulation software can input STEP or DXF files so I could run simulations to check what size and quantity of bar I need? 

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Thanks!!