Thank you. I took more time to do further reading and for the code stress calcs Ec is required and for simple systems 119.10 may be used to calculate Rh and Rc.
I am moving forward with Ec load cases for 31.1 compliance and Eh for support and equipment load calcs.
I am currently working with B31.1-2018 in CII v.12, project started before 2020 took effect and C2 isn't current w/B31.1-2020 as yet.
I understand flexibility calculations per B31.1 Para. 119.6.4 and 104.8.3 eq. 17 require Ec, but what about 104.8.1 Eq. 15 and 104.8.2 Eq. 16, or calculating...