how to add the mass of those supports in model corrcetly

Dear all,

when model a piping ,i want to add the weight of those supports (such as clamp, stand) in to the model, in order to make the model more close to reality, not only in static analysis but also in dynamic analysis.

How to do it correctly?!

thanks

Best Regards,

Specify force Fy in the model at these locations and put the wts.Remember these are static loads.Some significant effect can be in the consideration of the spring hardware for springs on large diameter lines.

In the dynamic analysis model you can add lumped mass at these locations.

Regards

thank you!

what you have advised is a way to solve the problem,

I figout out another way: model a very short rigid element connect to the node which will set a clamp. the weight of the element is the weight of a clamp
so in dynamic analysis ,i need't add lumped mass.
dose this way ok?

Also i think Caesar II　can modify the software to make it more easy to attach mass to certain node ,furmore ,can input center of gravity　of the attached mass by input dx,dy,dz from the node.

The question is...
What kind of support do have ?

You have a short support with high stiffnes ?
Then the mass is not imported for the pipe.

Do you have long flexible supports in relation to the pipe,then this mass and stiffness will be have
a imported influence in dynamic calculation.

The accuratest way is then build the support with structure element and take Cnodes.

for example:
a horizontal piping: 10----20-----30-----40,
if i want to add the clamp weight on node 30, i input: 30-301 dy=2mm or -2mm , weight= 500N,and
on node 30, i set a +Y restraint,
i think ,thus, stiffness is not a problem.

need your comments, Ohliger,
thank you!

at first ,i misunderstand Ohliger,haw-haw.

In the static load case the reaction from the clampweight goes direct in the Y support.
The pipe see not a stress from this, if the support have a high stiffnes.
Only the support see this forces.
Right ?

my example may be not a good one, change the restrain at node 30 to a spring hanger maybe better, the main purpose to add the weight of clamp is to corrcetly choose spring.

I would prefer the very short rigid element with the appropriate weight specified over the applied force when dynamics are involved. C2 will include the rigid weight in the mass model, the force will not. Both models should produce similar results for static analysis as long as you include the force set in the load case. (C2 considers all applied forces F1-F9 as possibly occasional loads and does not include them in the recommended load cases.)

I use the short rigid element to make it easy to enter the weight. Hopefully, the stiffness modification will be insignificant.

If you use a force, then you will have to adjust the mass model by hand by re-entering the total mass at the appropriate nodes.

Hopefully, the stiffness modification will be insignificant.

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sir, what the above sentence mean? can you explain it more detaily.

thank you!

Well, if you insert an arbitrary rigid element between two pipes, it will affect the stiffness of the system, and yield inaccurate results. The correct way to do this is cantilever the rigid element off of a node, so it affects nothing.

Richard,

can you modify the software to make it more easy to attach mass to certain node ,furthmore ,can input center of gravity　of the attached mass by input dx,dy,dz from the node.

in this way ,we need not cantilever so many rigid element off of all these support/hanger node,

second,
my example:
a horizontal piping: 10----20-----30-----40,
if i want to add the clamp weight on node 30, i input: 30-301 dy=2mm or -2mm , weight= 500N,and
on node 30, i set a spring hanger,

this example mean i cantilever the rigid elemet off the node 30, rigid elemet 30-301's centerline are viertical but the pipe centerline is horizontal.

best regard,