Previously I've dealt with piping systems in relatively low seismic zones so horizontal acceleration by itself was considered. In a new project with much higher seismic values we'll be looking to combine the horizontal and vertical components. Based off the Caesar II user guide, the load cases (shortened/condensed here) are intended to be:
L1 = Operating
L2 = Operating + U1 (horizontal)
L3 = Operating + U2 (vertical)
L4 = Sustained
L5 = L2 - L1 (algebraic)
L6 = L3 - L1
L7 = L5 + L6 (SRSS)
L8 = L4 + L7 (abs or scalar)

My questions:
1) The Caesar II user guide has another example where the operating case as "Operating + U1 + 0.67U2". Is there any difference in stresses/restraint loads between this load case and the method shown above? If so, what drives the decision to use either method?
2) I assume the L7 SRSS case (combining U1 & U2 before adding to the sustained) is another intermediate case that can be suppressed in the output (no restraint forces, displacement, or stress values to review). Is this accurate?


Thanks,