Answer to Statement 1: I have checked the INACTIVE ELEMENTS COMMAND and it seems to be working well. I think your statement comes from the fact of encountering an error while coming out of the editor. There appears to be an issue with the GUI not recognizing this command, which why that error is thrown. However, the engine does not have problems processing this command and the file would run without any problems with this command being used. Yes, the INACTIVE MEMBERS command will work as well.
Answer to Statement 2: These warning messages relate to ORPHAN NODES and ZERO STIFFNESS are thrown simultaneously as the geometry and the stiffness matrix is processed. Hence, these messages will show up even if the elements attached to these nodes are activated in the next step.
Answer to Statement 3: Where are you looking for the stress results? Post-Porcessing? In that case it would be worth noting that the results shown there will always be the results from the last analysis - which in your case means when all the plates are activated.
It would also be worth mentioning, that in STAAD we do not have a way of assessing the construction sequence loading, as we do not have a way of modeling the inactive parts on the initial deflected structure.
Answer to Statement 2: These warning messages relate to ORPHAN NODES and ZERO STIFFNESS are thrown simultaneously as the geometry and the stiffness matrix is processed. Hence, these messages will show up even if the elements attached to these nodes are activated in the next step.
Answer to Statement 3: Where are you looking for the stress results? Post-Porcessing? In that case it would be worth noting that the results shown there will always be the results from the last analysis - which in your case means when all the plates are activated.
It would also be worth mentioning, that in STAAD we do not have a way of assessing the construction sequence loading, as we do not have a way of modeling the inactive parts on the initial deflected structure.