im new in stress analysis field
i would like to know why in CAESAR code stress is not checked in operating condition.
also in 31.1 /31.3 codes do not consider the operating condition to be stress condition.

Ok so your question is basically why and how did the codes develop... I suggest you study and ponder on this in your own time by reading some of the many numerous text books available on the subject matter....

Look at the reading list on this web site as well as the newsletters... come back afterwards and then ask the question.... you should be absent a few years before coming back....

... and - this is a very common question. So common in fact that there is a post (permanently) near the top of this forum http://www.coade.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=9084&page=1#Post9084 that discusses this exact question.

You can also find the answer to many question by using the [Search] option, located just above the Calendar to the right. (Note, the [Search] option is only available if you're logged in.)