Hi....dear all

I only have a vague figure about LOAD CASE including seismic load.
Is there anyone who can help me get the clear picture of that?

I know that general load case including seismic load is ;

case 1 W1+T1+P1(OPE)
case 2 w1+P1(SUS)
case 3 W1+T1+P1+U1(OPE)
case 4 L1-L2(EXP)
case 5 L3-L1(OCC)
case 6 L2+L5(OCC)

I've already read the Technical reference manual.
but still I'm not confident.

Question 1 :
Why should I use "the load case 5" to get the seismic effect on the piping in the operating condition. Why is "load case 3" unavailable?

Question 2 :
When I make an analysis of an operating condition which is concurrent with seismic effect, Can I use the "LOAD CASE 7 L1+L5"?

Question 3 :
In technical reference chapter 6 page 23, It says the Load case 6 is "code stress for occasional load".
What does "code stress" mean here.

I deeply appreciate your help in advance.

thank you.

Answer 1: The code wants you to combine the Sustained Stresses with the Occasional Stresses. Case 2 gives you the Sustained stresses. How do you get the Occasional stresses?

In a perfectly linear system, you could setup a load case with just U1, and combine those stresses with case 2. However, for the general (non-linear) case, this won't work because you have not considered the status of the non-linear restraints. This is why you need case 5. Case 5 yields the effects of the seismic event, considering the non-linear restraint positions.

Answer 2: I wouldn't suggest that, use case 3 instead. Case 3 is important for displacement and restraint considerations (and it is needed to obtain the occasional stresses as discussed above).

Answer 3: The various piping codes typically consider a number of different load conditions: Sustained, Expansion, and Occasional. Each of these conditions causes a stress in the pipe, which must be computed according to an equation defined by the Code. This stress, computed as per a Code Equation is referred to as a Code Stress.