Dear Mr. Akila,

I also had the same doubt earlier, one additional information is that, Case-2 gives a very less value compared to case-3 and case-4.

Secondly,Case-3 and Case-4 gives equal value, and finally as per Coade example problem, SN-Fail, Coade followed the Case-3, which is giving more value and is equal to case-4.

So for time-history analysis the force combination is still puzzle.

I request Mr.Richard Ay and Mr.Dave to clarify this...