I modelled a fuselage using QUAD4's for Skin, CShear for frames and rods for the inner chord, outer chord and stringers. When i run a modal analysis, i get a fatal error and i see all the cshear nodes failing in 1,4,5,6 directions. The static analysis did run fine but i get the following out of plane displacement at the frames. There are no free edges no duplicate nodes as well. Please let me know if i am missing something.
Have you included the flange of the frames using CROD elements that will give the shear panel out of plane stiffness? - is that your chords?
Also, see image below detailing interesting comment on using CSHEAR:
Thank you for your valuable inputs. I found the mistake. A few of the nodes on both of the frames were out of plane by 0.1 inch and that was the primary reason. I corrected it and now the deflection is quite normal.