I tried .stl but fixing .stl model is a big project in itself. One thing that I did is I took the solution and entered into a new analysis as below:

However, the beam elements twist when I entered the model from one analysis (Step 1) into another (Step 2):

first step:

2nd step:

the beam elements are connected to a few shell elements. the shell elements come to the 2nd step of the analysis very good but the beam elements twist and rotate.

Any solution?