Dear All,

is it correct that dynamic- seismic analysis fot the above ground piping on piperack without adding the structural support file. ( +Y SUPPORT consider on piping input file)

i believe that earthquake may affect piperack first

please clarify in this regards.


regards

You are correct. The system "sees" the seismic event through the restraints. Applying the ground spectra to the pipe supports up in the rack isn't accurate, since the rack's stiffness comes into play (and in actual fact it is the rack supports that see the seismic event, not the pipe supports on the rack).

Either model the rack (and put the pipe on the rack), or impose a modified spectrum on the pipe supports.

Hi PipeHawk, if your interest is the Piping, and not the piperack, You haven't any problem, only is that your Desing Spectrum table,(Determined at the ground) Will be applied directly to the piping, without the "help" That the mass contribution of the piperack or other structures, can give to the dynamic event damping the efect and in consecuence the displacements, Mr. Ay opinion is Ok, The "accurate" for the support is wrong, but this is a "conservative" situation and not a omition input, but if your result are not ok, start to add these mass.

Regards

I think direct applying ground motion on piping is not the correct way. as pipe rack is having a finite stiffness and damping ratio which can be amplyfy the motion.
The best way is to talk with structural group if they are ready to give you the response of ground motion (earthquake Response spectrum)at particular elevation of pipe rack (Piping support elevation).

In the vertical direction, the same spectrum can be used ( as with the portion of the piping on the ground). For the horizontal direction, as Raju Soni points out structural group has to provide the information on response sectrum at that level. This has to be done using time history method, details of which can be found in Nuclear Regulatory Guide 1.122.Provide this document to structural group if they need it.

Regards