When I model earthquake as uniform load, (static analysis), I have to activate the "uniform loads in G's" option in special execution parameters tab, and then put in uniform loads section the ground acceleration value (0.24 in my case).

Is that correct?

Yes.

Yes, you will see the units in the Help (F1) and the tool tip fly-out will show "g" rather than the "load/length" units.

Remember that these uniform loads are not automatically included in the program-recommended load cases. You'll have to build them in yourself.

If your system has only linear boundary conditions, you can collect your occasional stresses from the uniform load (U) analyzed by itself. Otherwise, we suggest you run operating+U and then subtract the operating response from the operating+U response to collect those stresses.

And when combining sustained and occasional stresses, use "Scalar" rather than "Algebraic" summation (set on the Load Case Options tab).

As I know, even +Y Restrains are not linear (practically All piping Systems)

Thank You.

Hello!

I would have one question regarding your reply:
What if I'm using for the occasional load the cold sustained (W+P1+U1 for example)? Even with non-linear restraints. That is not considering the thermal influence, except for the sustained allowables...right?

I have attached 2 files in which I have tested the difference between the 2 ways of defining the occasional loads:
a)L5 W+P1+U1 (OCC)

b)L1 W+P1+T1
L2 W+P1+T1+U1
L3 L2-L1
L4 SUS + L3 (OCC)

And I find there are differences in between the results
Can you please point out the right way of doing things? And why?

Thanks

Method (B) is the recommended procedure because it accounts for the change in non-linear boundary conditions. Method (A) does not.

Hello, everybody!

One more argument in favour to Mr. Ay's response:

Case (a) does not meet entirely ASME B31 Piping Codes provisions related to Occasional Stresses checking/limitation.

So, ASME B31.3 stipulates at par. 302.3.6(a) that "...the sum of the longitudinal STRESSES SL due to sustained loads, such as pressure and weight, AND OF THE STRESSES produced by Occasional loads, such as wind or earthquake, may be as much as 1.33 times the basic allowable...".
Therefore, the absolute values of SUStained stresses and Occasional stresses should be summed, as Caesar II performs when scalar summation is correctly prescribed by the user for (b)L4 case (which should be anyway corrected by replacing "SUS" with the suitable sustained loading case W+P1 that must be previously defined).

The same principle is employed in eq. (12) from par. 104.8.2 of B31.1 Code.

So, method (b) corresponds to the most usual piping design codes principles.

Regards,

Your question has also another component "[…] put in uniform loads section the ground acceleration value”, (0.24 in my case). Is that correct?"

Yes or No--It depends on the specification you must follow. If there’s one to follow.
You may download the Coade Mechanical Engineering News Oct 2002, which include an excellent article by Mr. Dave Diehl. "Current approach to Defining Ground Motion".

The "Closing" section shall give you some additional question marks on which acceleration you must consider...

Regards,

Hello Everybody...

For Mr. Ay's and Mr.Dave i have a question:
What about if i have three (3) cases of OPERATING to check in Non-linear boundary condition, Which OPERATING case should i add to the Seismic Acceleration (U1,U2,U3)?
Could you give an examle set of case?
And for all this time i always Sum SUS+OCC use ABSOLUTE, is it wrong?

There has been a code interpretation handed down by B31.1 and B31.3 in this matter... in essence it says All must be considered (with the idea in mind that the worst case is taken care of)

I wrote the requests to both committees helped answer one of them and that is the essence of the matter.

Follow method (b) above...