What might be reason for Check value not being zero

[nany717]

Hi

I have modeled a simple container configuration, in which i have to test for the reactions when subjected to accelerations. When I solve the model, i can see the sum of reactions is not equal to the sum of forces. 

What might be the reasons for this mismatch !? can someone point out, where I went wrong !

I have attached the model for reference. 

[Artur.Kosakowski · Accepted solution]

Ignored instability due to wrong material properties.

BTW: check if RECT_1 section is defined correctly (values should be in mm or cm)?

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[nany717]

Yes Artur, 

I intentionally created a dummy material without any properties, or very very less values for all the properties. 

How else can I model a container (of 25 ton weight) sitting on beams (HEB300), which are fastened to the deck/floor by welding ? 

The problem arises only with Y+/Y- acceleration cases, for the rest of the cases, it is giving the results as expected. Also, when I change the support spring stiffness even by 1kN/m value, the error is getting bigger and bigger. Please guide. 

[Artur.Kosakowski]

As a nodal mass in its center of gravity with rigid links to connect it to the beams?

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[nany717]

Yes, like that...

[nany717]

Also, Artur

Is there any problem in using Spring supports instead of Pinned/Fixed. I am seeing some odd reactions.

Will there be any internal reactions generated because of the springs ?!

[Artur.Kosakowski]

Should not be. Any instability reported?

[nany717]

No instability reported. 

I have attached the file. 

See case2: HP Pump Weight. Check the reactions in Y direction. Strange!

This is the dead weight sitting on two beams, from your earlier suggestions, I am using good material properties.

[Artur.Kosakowski]

I'd define the rigid link in a different way.

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[nany717]

I can see that the unwanted reactions got reduced.

but still, why am I getting those reaction forces in Y when I am applying Z acceleration on added mass ?!

 

[Artur.Kosakowski]

Due to the small bending of dummy bars at the locations with no rigid links which could not be defined as you already defined other rigid links there. If this is a concern you can replace one group of them with rigid bar elements.

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