## Robot Structural Analysis

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# Substructure concept

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Dear All,

Please refer to attached picture, what type of method should I apply in RSA, if I want to simplify the model. For example shown purlins in picture are consuming so much effort of RSA solver engine whereas I think they can be eliminated and can be assumed to be represented as load transfering objects in overall mechanisms. If those purlins can be simplified with sub-structuring also I will appreciate any step by step guide, because RSA manual doesn't help me a lot.

If there was any other more robust or effective method in RSA that I'm not conversant please mention it.

Regards,

Solved! Go to Solution.

# Re: Substructure concept

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I'm not sure if I understand you correctly but you can define the purlins in one model and calculate the reactions which you can then convert into nodal loads for another model where purlins are e.g. replaced by horizontal supports along the rafters.

See also:

*If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.*

**Artur Kosakowski**

# Re: Substructure concept

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Artur.Kosakowski wrote:I'm not sure if I understand you correctly but you can define the purlins in one model and calculate the reactions which you can then convert into nodal loads for another model where purlins are e.g. replaced by horizontal supports along the rafters.

Yes, this is another alternative to find the solution but if you have too much load cases then that task may not be a trivial. Because for each single load case you have to find the nodal forces and must apply it to the original system, actually I was looking for more automatic way in RSA.

I thought that substructuring mechanism was developed only for that purposes. But I have no clue on how it really operates or how can be used to simplify the original model. Can you elaborate that a bit further ?

Regards,

# Re: Substructure concept

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Yes, this is another alternative to find the solution but if you have too much load cases then that task may not be a trivial. Because for each single load case you have to find the nodal forces and must apply it to the original system, actually I was looking for more automatic way in RSA.

The Rafal's macro is intended to make this process automatic provided the numbers assigned to supported nodes in one model are the same as numbers of nodes to which the load converted from values of reactions are to be applied.

I thought that substructuring mechanism was developed only for that purposes. But I have no clue on how it really operates or how can be used to simplify the original model. Can you elaborate that a bit further ?

The substructure concept is a bit different. Having a large model with huge amount of results you can decide on selection a part of it and save it as a substructure. Then you can explore the results for this part only which should be faster as the amount f data is reduced.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

**Artur Kosakowski**

# Re: Substructure concept

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Artur.Kosakowski wrote:

The substructure concept is a bit different. Having a large model with huge amount of results you can decide on selection a part of it and save it as a substructure. Then you can explore the results for this part only which should be faster as the amount f data is reduced.

Thanks in advance,

So this substructuring concept differs from those which defined in FEM methodology. In FEM substructuring is used as preliminary step or steps to solve huge problems which depends on substructure results.

But in RSA its more like a for end-user convenience when dealing with huge problems. Please confirm ?

Regards,

# Re: Substructure concept

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I think you may say that in this way but you can also use this small part of the model for analysis too (e.g. selected slab of a multi story building with columns and walls replaced by supports).

**Artur Kosakowski**