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Linear releases and material orthotropy

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Message 1 of 4
robertkettleborough
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Linear releases and material orthotropy

We are modelling an existing 9 storey RC building from as built drawings in order to model potential changes being made to the building. The building has slabs that are 2-way spanning or 1-way spanning in both the x and y direction. The slabs are effectively pinned to the supporting beams in some perimeter locations (in many internal locations the slab spans continuously over the supporting beams).

 

The below image is an example section (within a much larger building) of what we are trying to achieve. It shows the various slab directions with the red lines showing the linear releases we are trying to input. 

 

Diagram.png

 

To model the 1-way spanning slabs we have applied material orthotropy using 1/0.01 n factors. Where there is no slab continuity we need to apply linear releases in order to prevent moment transfer into the supporting beam. However, when applying orthotropy and linear releases together we are having some problems with type 3 instability errors occurring. The nodes referenced in these errors are often at the calculation point nodes created by the linear releases rather than actual modelling nodes. As a result we are unable to get all the releases we want into model without instability errors.

 

Could anyone provide any advice on why these errors might be occurring, and any way we can get around the issue? Is using material orthotropy and linear releases for different span directions on adjacent panels causing too big a difference in values in the stiffness matrix? When we have released all 4 sides of a panel we have already applied the Rz support in the panel centre as per previous posts so we don’t think that is the issue.

 

We have attached the model below if anyone has chance to have a look.

http://www.filemail.com/d/jsjzfocijpnlfmy

 

Thanks for any help you can provide.

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Message 2 of 4

When we have released all 4 sides of a panel we have already applied the Rz support in the panel centre as per previous posts so we don’t think that is the issue.

 

THis is correct approach in this case.

 

The other instability is mathematical instability and can be neglected.

The way how to check it below:

 

rx11.jpg



Rafal Gaweda
Message 3 of 4

Thanks for your help with that.

Could you clarify whether this also applies to calculation nodes with similar instabilities if we chaeck that the results are zero in the results table?

Many thanks in advance.

Message 4 of 4

If understood you correctly the answer is yes.


Rafal Gaweda

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