There are two options:

1) Go in for a Finite element analysis

2) Use the well known Kellog formula.

I don't think you will go in for option 1.

So far option 2 is concerned, if you have the M.W, Kellog book you can use the same. Else go in for www.engg-tips.com where in "search" you need to type the word "trunnion". You will find no. of answers where this expression taken from M.W, Kellog is used, with a note as to how to add stresses.

So far addition of stresses is concerned, use your own judmenet as the M.W. Kellod formula does not suggest anything on that. You can use the recommendations given in ASME Sec VIII Div 2 Appendix 4 for the stress summation part,by judiciously categorising the stresses.

Anindya Bhattacharya