Hi, I have a pipe line with external forces acting on it. Could you tell me if these load cases are correct to satisfy B31.3 code?

1 (OPE) W+D+T+P+F
2 (SUS) W+P+F
3 (EXP) L1-L2

Force F is vertical and I added it to simulate weight of another line (let's say it's a boundary condition).

Hi Ferex
I think you are right.
If F is just a additional vertical weight, you can add a rigid body at that location of piping & put rigid weight.

Regards

Habib

Yes but be sure to add that F1 in the load cases. CAESAR II will not recommend F's.

Shr why should I use rigid body? Isn't right to add a vertical force and then configure the load cases as suggested by mr. Diehl?

Assuming this "force" represents an actual "part" of the system, and is therefore a "primary (weight)" load, then there are a number of reasons to opt for the "rigid element" technique rather than the "Fn" technique:

1) By using a "rigid element" of the appropriate weight, this weight will always be included in the system analysis when the load case contains either "W" or "WNC". There is no chance that you'll forget to include "Fn" when you setup a new load case.

2) Should you ever need to perform dynamic analysis on the system (maybe not you, but someone else a few years from now), the mass of the "rigid element" would be automatically included in the system mass matrix. The "Fn" on the other hand would not be included, and to "correct" the dynamic model you would have to include a "lumped mass" in the dynamic input. This is because we don't know what the "Fn" vector means - is it a mass (i.e. part of the system), or some type of load?

Set things up to be "simple", "obvious", and in a manner that hopefully prevents you from "shooting yourself in the foot" sometime in the future. I'd use the "rigid element". Just make it 1" long with the appropriate weight, and attach it to the node where you would have applied the force.

Many thanks.
If I am right in case L3 force F should not be taken into account by the software but I noticed that friction acts as the vertical force (which of course generates friction) is still present... this sound a little strange to me.

Case 3 is the "difference" between Cases 1 and 2. So there could be "effects" of load redistribution in Case 3, which if you have friciton defined, would also contribute to the results.

So finite element calculation is taken only on case 1 and 2, and for case 3 Caesar does only algebric sum, right??

Yes.

Hi Richard

Just one clarification, caesar follow finite element method or structural beam theory for calculation.

Regards

Habib

FEA using the "3D Beam Element".

Thanks Richard


Habib