Virtual load cases are used in Express for deflection limit optimizations. They are required for the adjoint solution. More detail on the theory can be found in 'Kyung K. Choi, Nam H. Kim: Structural Sensitivity Analysis and Optimization 1'. In most cases, the proper virtual load cases will be generated automatically (simply by defining a deflection limit).
In particular cases, users might want to manually create virtual load cases. Load cases flagged 'virtual' on import can be paired with 'actual' load cases in the stiffness deflection limit definition. Virtual load cases will NOT be accounted for in the strength sizing routine.
