RE: Weld Design for HSS to HSS Member in Staad

You need to add the SELECT WELD command as shown in the example below

PARAMETER
CODE AISC
WELD ...
WSTR ...
...
SELECT WELD MEMB 1 TO 10

Having mentioned that, you should also take a look at the wiki below

communities.bentley.com/.../28130.weld-design-in-staad-pro