Dear all,

Rigid strut and Rigid hanger rods by assembly & configuration are two different kind of supports. But modelling philisophy in CAESAR II is same i.e. +Y rod.

What are the factors we need to be considered to differentiate the same while modelling in CAESAR II??

Reagrds,

The only thing is that you have to remember that hanger rods are not appropiate for compression loads. For +YRod, check the actual load, if is sign plus, mean that you have to change something.

Thanks.

"For +YRod, check the actual load, if is sign plus, mean that you have to change something." - why such thing should happen ? Is the any error in "+YRod" modelling in Caesar-II ?
reg,
sam

No error. Referencing only Y (vertical) here:

In CAESAR II you have +YROD & -YROD. These indicate the position of the pivot point of the rod: +YROD pivots above the pipe and -YROD rotates about a point below the pipe. If you enter YROD, the program will change that to a +YROD. There is no lift off of these supports, the nonlinearity is that the pipe is constrained to follow an arc rather than stay in a plane (e.g., +Y).

What Dan says is that you should review the direction of the support load (pull or push) to determine if the rod is in tension or compression. If tension - all is OK; if compression, there may be liftoff or even buckling.

Indeed.

With reference at your query regarding the use of horizontal rod near a pump nozzle (that you edit it and deleted), this is different. But this is interesting.

Caesar have + or - xrod or zrod. Treat them as rigid struts. And yes, there are huge differences if you use +xrod or x or -xrod near the pump. But this is because is not recommended to use a support very close to an anchor point (pump nozzle). Remember Archimede. Any small influence from outside will have big impact on the other side.
Placing a support nearby an nozzle "in order to protect" a nozzle will have a different effect.

Regards,

From Dave & Dan Sirs clarification, are we to understand that YROD and + YROD are same and have zero stiffness in +Y direction, so it can lift or buckle which a rigid strut can not!
Reg,
Sam

No.

If you enter YROD, the program will change that to a +YROD.

This will mean that support is placed above the pipe.
+YROD do not have zero stiffness in +Y direction. Caesar makes no difference between Rigid strut or a hanger rod. It is your responsibility to check that if you use a real hanger rod you do not have upward forces.

I hope that now is clear.

Regards,

Sorry to bother you again! If +YROD is similar to Y .. I can use +Y for strut in vertical direction. If not and +YROD is like +Y .. one with high rotation provision and other with small rotation provision, then +YROD is reLly a rod hanger, not a strut. For large rotation rigid strut in Y direction, is there any restraint in CAESAR II stable ?
Reg,
Sam

No bother.
See the attached file at node no 30, 1030 and 2030 and study the differences.

Now study the other file.

Aside -
If you wish to have a +YROD model that can actually lift off (disengage), you can CNode that +YROD and define a +Y restraint for the CNode and lock down that CNode from horizontal translation (e.g., either 0 displacements in X & Z or provide restraints in X & Z).

The reason for my query whether large rotation rod assumption is right for indiscriminate use for rigid Struts in piping in a high seismic zone near sensitive equipment nozzles!
Can we model the same rigid strut having large rotation by any other way in CAESAR II?
We are dealing with pipes here ..not like truss in structures. So far I remember there is caution in application guide against over use of this restraint!
Are our forum members using large rotation rods or x,y,z for rigid Struts .. if so, why not large rotation rods as suggested in this discussion ?

Reg,
Sam
I am sorry for cautious approach as we are from nuke era of questioning till we get satisfied!

Can rigid strut be made by joining the pivot node with pipe node with a rigid pipe by having xyz translation stopped both at pipe node and pivot node, but keeping rotational xyz free?
I need to chk large rotation rod effect by some independent simulation in CAESAR II to use for rigid struts!
Reg,

why not?

you can refine further you model, for example insert a rigid from pipe centerline to outside the pipe, or you may apply a rotational restraint in one direction in one side and perpendicular another one on the other side. It's up to you how refined you want to model this rod.

The people that use simple X or Z restraints may tell you that they do not need further refinement of the model.

Regards,

As solution results vary with rod increment and rod tolerance in Caesar ii config for rod restraints, I am a bit sceptical about the accuracy, if done on a regular basis. Otherwise, approach of this is well established since long as shown in nov87 of men publication of Caesar ii.


Reg,sam