Implement IFCStructuralLoadLinearForce and IFCStructuralPlanarForce in the BIM module

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l_pereztato
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Implement IFCStructuralLoadLinearForce and IFCStructuralPlanarForce in the BIM module

Post by l_pereztato »

Hi.

I'm using the FreeCAD BIM module to create FEM models and import them to XC. I've no problems defining the model geometry, but when trying to define loads I've noticed that IFCStructuralLoadLinearForce and IFCStructuralPlanarForce are not implemented yet.

Could you put me in the right direction to implement those IFC entities in the BIM module?

Thanks a lot for your work.
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bernd
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Re: Implement IFCStructuralLoadLinearForce and IFCStructuralPlanarForce in the BIM module

Post by bernd »

Hi Luis,

should we really implement it in the BIM-Module ... ?

A slab has constant distributed load, but mostly is modeled by more the one geometrical element.

It might be better to implement it not inside the FreeCAD BIM objects as Attributes, because we would need to flood the objects with attributes. Might be better to create own load objects which have the slab objects they belong to as a PropertyLink. Every load type gets its own object. One slab live load object could even have links to all slabs from all floors with this load.

Similar to FEM load object in FreeCAD.

This information from the new object we could export to structural ifc, oder directly use to create FreeCAD FEM analysis.
l_pereztato
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Re: Implement IFCStructuralLoadLinearForce and IFCStructuralPlanarForce in the BIM module

Post by l_pereztato »

Hi, Bernd! Thanks for your reply.

Maybe I'm wrong, but I don't think that those attributes are intended to be used on the geometrical objects used to define the structural element. I think they must be used with the corresponding IfcStructuralSurfaceAction which can contain an IfcFaceSurface that defines the loaded part of the model. This way you can define loaded surfaces that are not directly related to structural elements, and you can use any shape as a loaded surface. I think this is also compatible with the case you described in your reply.

I don't know if it's better to implement this outside the BIM module, but I think that the implementation I've roughly described above doesn't need to extend the attributes of the existing entities; you define the IfcStructuralSurfaceAction and the corresponding surface and IfcStructuralPlanarForce (or the corresponding linear or punctual counterparts). Then, it's the preprocessor of the finite element program which computes which elements must be loaded.

What do you think?
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yorik
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Re: Implement IFCStructuralLoadLinearForce and IFCStructuralPlanarForce in the BIM module

Post by yorik »

I always wanted to somehow reuse in BIM the forces system used in FEM... But there are many way something like that could be done (is it FEM forces that could be applied on non-FEM objects? Or is that another kind of object that could be used in FEM to generate FEM forces automatically?)

In any case the idea is interesting... Indeed it seems possible to have a fully rigged structural model in IFC, with forces and everything. And some of them could even be deduced automatically (for ex the weight of a beam from its volume * mass) in FreeCAD, there is a vast field to explore there
l_pereztato
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Re: Implement IFCStructuralLoadLinearForce and IFCStructuralPlanarForce in the BIM module

Post by l_pereztato »

Hi.

I'm trying to get a better understanding about IFC load definition, and I'll return with my thoughts. Nevertheless, I think that the model must be as «FEM agnostic» as possible, namely, you define the geometry, the materials and the loads (the geometry and the values of the loads) and then it is the analysis program responsibility (finite element or not) to deal with the model.
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bernd
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Re: Implement IFCStructuralLoadLinearForce and IFCStructuralPlanarForce in the BIM module

Post by bernd »

FreeCAD FEM has lots of examples in menue utilities. They may help to see how it works in FreeCAD FEM.

You can apply loads to any Arch object even a stair or a covering. The Arch object type does not matter at all in this case because the underlying geometry is used directly. More a problem will be the arch object is a volume geometry but the load should be applied not to one of the geometry faces but on the structural axis face instead.
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yorik
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Re: Implement IFCStructuralLoadLinearForce and IFCStructuralPlanarForce in the BIM module

Post by yorik »

Can you apply FEM forces to a wire or edge?
The axis of an arch structure could become an actual edge...
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Re: Implement IFCStructuralLoadLinearForce and IFCStructuralPlanarForce in the BIM module

Post by bernd »

sure.
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