STAAD is a software that's capable of running both first order and second order analysis. Second order analysis accounts for small and big delta. You can go to
Note, Staad 2007 doesn't have small delta effect turned on by default, but I think it does for STAAD.Pro V8i. Try the command PDELTA n ANALYSIS SMALLDELTA, where you replace [n] usually by a number greater than 15. If you need more help on the Staad Pro, it would be helpful to visit
Thanks ISCK. These links are really helpful.May I ask more question?
What are the difference in the design between 2D frame and 3D frame analysis? Does 3D frame is used in actual analysis and design of the structural members? Are the beams will be also be design using the moment from PDelta Analysis?