We've run seismic analyses where we have included in the model displacements to account for building drift. These displacements were "large" - say 4" to 6" - so it's easy to accept the fact that they need to be accounted for in CAESAR. However, we now have a structural steel pipe bridge which the structural folks say will deflect 1-1/2" down under load. So our usual assumption that the support steel is "fixed" is not valid. We either stiffen the steel to get to something acceptable, whatever that is, or model the steel in CAESAR and see what happens. Are there any guidelines to indicate when the support steel can be assumed fixed and when its deflection needs to be accounted for?

What is the reply for this post?? anyone...??I have the same query..
My piping is running between two buildings of different height..Seismic movements can be 150 mm each building..worst case possible, the buildings can move in opposite direction with 300 mm relative movement..how to give this in CAESAR???

In the Dynamic Input for the "Spectrum Load Cases", you would enter these displacement values in the far right column (Anchor Movement).

Dear richard,

why we do not put this seismic displacements as displacement boundary condition in CII with out go to dynamic analysis.

best regards

Because those displacements are really only applicable to dynamic spectrum analysis.

When we do a static seismic analysis, we put construction nodes on the restraints and apply the building displacements as vectors on those C-nodes. We just have to make sure to catch all the restraints on the building section moving. Usually we do 2-4 orthogonal directions depending on the pipe routing (lateral to piping axis and into/away from pipe axis). For tank nozzles I resolve the tank motion to the axes of the nozzle (which rarely matches the piping coordinate system).

And if you don't mind, how you consider the displacements? primary or secondary?

Regards,