Timely discussion. I was just today arguing with my team about combining SUS+U+D for code compliance. My position is that the piping maximum acceleration will be roughly concurrent with peak displacement for a restrained piping system so SUS + U + D is the correct combo for code. This matches up with Itchy's post I think. Restraints would be OPER + U + D.

Just last week I finally had a loud enough argument with my structural guys to get clarification that their "ASD" design = real world force reactions. Per Mariog's last note, this would work out to 0.7 x ASCE acceleration (Fp/WP as used in ASCE 7-05 EQ 13.3-1). My structural people are still non-committal on reducing their SAM displacements which is blowing out my current piping analysis.

With regards to mitalia2009's question about ASCE spectrum - I'm taking the R value reduction noted in the CAESAR help file (~3.5 R value per ASCE tables in chapter 12) which brought the spectrum response down around the ASCE equation 13.3-1 accelerations. Would be interested to hear the Integraph guru's discuss that a bit since those chpt 12 tables are for building structures as opposed to the Rp reductions in chapter 13.

If I was going to use an LRFD/Ultimate/MCE design earthquake similar to recent Sendai magnitude, I would take the additional stress allowances in B31E 3.4(vaguely similar to Section III Class D piping in my limited understanding) to approach/allow some plastic deformation which is beyond 31.1/B31.3 occasional allowables (1.5Sy >> 1.2x or 1.33x Sa respectively).