Thank you for posting this idea. There has been discussions in the past to extend the analysis methods in order to support an ability to define multiple analytical models in STAAD which are derived from a single analytical model. The effects from all the analysis sets used in part or fully in the design routines. This is very much at the heart of the ongoing physical model development.

As per many codes, particularly IS 1893 part-2 and IS 3370 part-2, the RCC elevated/underground water retaining structure should be analyse and design in "TANK ENPTY" and "TANK FULL" both of the conditions, but staad pro seismic definition wheather it is static /dynamic, analyse and design the RCC tank only for any one of condition in seismic case,either empty or full tank condition, both condtion one after other isn't support by staad, how to tackle this situation? There is one option that, we can make two stad files in two different folders one for empty and other for full condition, but here the governing load combination can not be identified, for reinforcement, crack width and other checks...