Thank you Mr. Diehl.
As you pointed out, B31.3-2014 still requires the stress range to be calculated using Ea, as per paragraph 319.4.4 (a).
Going back to the paragraph 319.5, I still doubt that ;
if the purpose of code change was just to allow code users to have options to use Em, instead of Ea, then the code should have said that "Ea shall be used, but Em may be used". But, the code changed to say that "Em shall be used, but Ea may be used".
In most cases using Ea will give us more conservative results in calculating reactions than Em will, but the difference in calculated reactions between using Ea and using Em, sometimes seems to be excessive to be considered as just "conservatism".
I think to be "conservative" in designing reactions, it would be better to have a safety factor to calculated loads, not to use higher elastic modulus.
Thank you.