I am using AISC code. How can I have STAAD do deflection check for service cases and do strength check for ultimate cases ?

For AISC 360-10, the design routine can do deflection checks based on SERVICEABILITY LOAD ENVELOPES and strength checks based on STRENGTH LOAD ENVELOPES as part of the same design cycle. One needs to define serviceability envelope and strength envelope first consisting of the appropriate cases and then define a LOAD LIST ENV command  for the design to consider these as explained below.

For example if you have a strength load case 10 and a serviceability case 11, you can set up the design as shown next

…

DEFINE ENVELOPE

11 ENVELOPE 1 TYPE SERVICEABILITY

10 ENVELOPE 2 TYPE STRENGTH

END DEFINE ENVELOPE

LOAD LIST ENVELOPE 1 2

PARAMETER

CODE AISC UNIFIED 2010

METHOD ASD

*specify all design parameters here including DFF, DJ1, DJ2

CHECK CODE ALL

…

The software would then use the Load case 11 for deflection check and load case 10 for strength checks.