The software you've mentioned has no support for Ubuntu. You will need to use a 3rd party application which emulates Windows environment in order to run/install the application.
The software that can help you is called Wine and it runs Staad very well. To install this application, open Terminal and type : sudo apt-get install Wine. You should wait a little because the downloading will take some time. Then you will find your application in the Applications folder in the Main Start menu.
From its main interface you can add the executable package for the Staad Pro. Basically you can proceed and use this method for all CAD software but the problem resides in the compatibility between Operating System -> Wine -> Cad Software.
