Dear Forum Members,
I am working on a piping system which is partially buried and partially above ground.Refer attached snapshot.I am using Earthquake(Spectrum) module of Caesar II. I am using client defined Spectrum @ 0.2% damping.

The set of vectors I have used is as follow.
X=1.0
Y=0.7
Z=1.0

The load case for Dynamic is as follow
D1 (Combination#1)
D1 + (W+P1) (Combination#2)
D1+(W+T1+P1) (Combination#3)

The method I follow to evaluate liftoff at dynamic is as follow:
Compare the loads at Static case [W+T1+P1] in +Y support(always negative) with loads at Y support(always absolute) for Dynamic Combination#3
[ D1+(W+T1+P1)]. If the load in static case
( say - 1000N) is less than that of dynamic case (say 1100N), then the support tend to lift off.
The question I want to ask is as follow:

(1)Is my approach toward liftoff correct?
(2 How do caesar II react in Earthquake Spectrum to a line which is
partially buried and connected to a above ground line.
(3)Is is Justfied to create a lift off case in static case for the support
that lift in dynamic case by removing those +Y support and comparing
sustain stresses with Sh?

Thanks in advance
Alkesh Bhati

Anindya sir, richard or Dave, please post your valuable comments on this topic. I am stuck up in issuing this system.

For selecting the load case for NON LINEAR RESTRAINT status which will then be "linearized" by the program, it is , in my opinion,best to take the operating case.Design case may make it very conservative. This is valid if you have +Y ( and other unidirectional supports). However if your supports are bi-directional like Y , excluding friction, linear and non linear status will be same.Remember, CAESAR II dynamic module is based on linear analysis.

Buried pipe will not be subjected to seismic inertia forces as inertia forces are based on absolute accelearation.The effect of seismic activities on buried pipes is something you cannot simulate in CAESAR II.To properly understand what you need to consider , refer an American Lifeline alliance document on the subject.

I don't hany any problem with your load cases.

Regards

In my opinion loads for dynamic combination#3 always would be grearer than loads for static case W+T1+P1 so my recommendation is comparing D1 with that static case would be better and if D1 is greater than W+P1+T1 it will make sure liftoff.

Thank you Anindya sir and Nioosha for your valuable reply. I will confirm this with american alliance book and will post its relevant page here if possible.