I know there is no calculation of leteral tee's SIF in b31.3. however when I saw output, Caesar 5.0 calculated SIF of leteral tee. Thanks to your answer, soon.
The only piping Code that provided a computation for lateral tees was (the French) CODETI. If any other piping Code is in use, and you saw an SIF other than "1.0", then it was manually entered by the user.
I believe CII will give you a WARNING that the lateral modeled (specified as a Tee) does not geometrically constitute a header and branch. The WARNING then explains how the SIFs are calculated by CII.