[IFC Export] Problems with IFC (structural view) export

[johnwang]

So I managed to come to this result:

This is cool.

Could you share a simple ifc file, I want to try to import it into Mystran/Nastran95. Thanks.

[balrobs]

So I managed to come to this result:

This is cool.

Could you share a simple ifc file, I want to try to import it into Mystran/Nastran95. Thanks.

Of course!
Here is the ifc file exported from FreeCad. Be aware that it comes with the limitation described in previously posts:

Test_IFC_3_storeys_01.ifc

(16.93 KiB) Downloaded 67 times

And here the ifc files exported from RFEM after the import and a simple structural analysis (self weight):

Test_IFC_3_storeys_02.ifc

(48.15 KiB) Downloaded 70 times

Have fun with it

[yorik]

I can't find this Nodes property for Arch Walls. Could this be the reason why for Walls the IFC-Exporter don't work

Yes. Indeed walls don't have that property. You should either model walls using the Structure tool (change their IFC type to Wall afterwards), or use the wall tool, then use the structure tool on top of it to convert it to structure (then change the IFC type). But indeed it would be useful to add the Nodes system to walls too. I'll take care of that.

I'll also fix the end vertex for slabs. Indeed that seems obvious.

About the rest, how to manipulate things... Indeed the best way would be to be able to select the nodes and move them around like any other geometry. Maybe an interesting workflow could be this:

1) You can model node lines manually, using lines and polylines
2) You can attach such a line or polyline to a structural object, for ex. a NodeObject property. If such property is set, the struct object derives its nodes from the attached object and not automatically anymore
3) You can move, trim, edit, rotate... the lines/polylines, the nodes will be automatically adjusted

About section properties and materials, that is already done actually, if you export a hybrid model with both the IFC product (beam, column...) and IFC structural element. But not sure how many softwares out there can use that... Maybe there is some better way?

[bernd]

None I know of. ATM materials an cros sections should be included in the structural analysis ifc.

[balrobs]

I can't find this Nodes property for Arch Walls. Could this be the reason why for Walls the IFC-Exporter don't work

Yes. Indeed walls don't have that property. You should either model walls using the Structure tool (change their IFC type to Wall afterwards), or use the wall tool, then use the structure tool on top of it to convert it to structure (then change the IFC type). But indeed it would be useful to add the Nodes system to walls too. I'll take care of that.

Thank you so much @yorik for taking care of this issue. It would be wonderfull if walls could have a Nodes system too.

I'll also fix the end vertex for slabs. Indeed that seems obvious.

Awesome! That would mean that this step would no longer be necessary in the further processing software.
BTW while you are on it ... what do you think about not creating IFCSTRUCTURALCURVEMEMBER's on the slab loop but instead a IFCSTRUCTURALSURFACEMEMBER for it. IMHO this shouldn't be too difficult and would be very helpfull for further structural analysis.
I took a look at some FreeCad generated IFC file and the IFC specifications trying to understand the changes required in this regard:

Current approach: now for every edge on the slab loop:

• create IFCEDGE
• create IFCTOPOLOGYREPRESENTATION for IFCEDGE
• create IFCPRODUCTDEFINITIONSHAPE for IFCTOPOLOGYREPRESENTATION
• create IFCSTRUCTURALCURVEMEMBER for IFCPRODUCTDEFINITIONSHAPE

Proposed approach: for every slab (hopefully correct ):

• create IFCEDGE for every edge on the slab loop (already done by now)
• create IFCORIENTEDEDGE(*,*,#IFCEDGE,.T.); for every edge on the slab loop
• create IFCEDGELOOP((list of IFCORIENTEDEDGE on the slab loop));
• create IFCFACEBOUND(#IFCEDGELOOP,.T.)
• create IFCPLANE (already done by now)
• create IFCFACESURFACE((#IFCFACEBOUND),#IFCPLANE,.T.);
• create IFCTOPOLOGYREPRESENTATION(#...,$,'Face',(#IFCFACESURFACE))
  
• create IFCPRODUCTDEFINITIONSHAPE($,$,(#IFCTOPOLOGYREPRESENTATION))
  
• create IFCSTRUCTURALSURFACEMEMBER('...',#...,'Slab',$,$,#..,#IFCPRODUCTDEFINITIONSHAPE,.SHELL,SLABTHICKNESS)

As an example I modeled a simple rectangular slab in FreeCad, exported the IFC file with the current approach and then modified it by hand accordingly to my proposed approach.

Screenshot.PNG (138.21 KiB) Viewed 2908 times

Rect_Slab.FCStd

(14.23 KiB) Downloaded 54 times

Rect_Slab_current_approach.ifc

(3.18 KiB) Downloaded 49 times

Rect_Slab_proposed_approach.ifc

(4.24 KiB) Downloaded 75 times

About the rest, how to manipulate things... Indeed the best way would be to be able to select the nodes and move them around like any other geometry. Maybe an interesting workflow could be this:

1) You can model node lines manually, using lines and polylines
2) You can attach such a line or polyline to a structural object, for ex. a NodeObject property. If such property is set, the struct object derives its nodes from the attached object and not automatically anymore
3) You can move, trim, edit, rotate... the lines/polylines, the nodes will be automatically adjusted

Indeed, this could be a way to go. If I understand you correctly, an advantage of this approach would be that e.g. slabs with circular borders could also be transferred to IFC. Am I right?

None I know of. ATM materials an cros sections should be included in the structural analysis ifc.

I will investigate further and will be back here when I found something useful!

Edit1: Corrections in proposed approach and appending sample files for a simple rectangular slab

[bernd]

None I know of. ATM materials an cros sections should be included in the structural analysis ifc.

I will investigate further and will be back here when I found something useful!

something to start with ... https://github.com/berndhahnebach/Ifc_S ... .ifc#L1615 and https://github.com/berndhahnebach/Ifc_S ... t.ifc#L211 there should be a surface member as well.

[balrobs]

...
something to start with ... https://github.com/berndhahnebach/Ifc_S ... .ifc#L1615 and https://github.com/berndhahnebach/Ifc_S ... t.ifc#L211 there should be a surface member as well.

Thank you @Bernd for the Links!

[balrobs]

According to my understandig StructuralSurfaceMember are not yet supported and the StructuralCurveMember generated instead on the contour are missing the contour closing member. That's too bad
Hopefully there will be someone with the necessary skills willing to pick up this issue and improve the IFC export. IMO this feature would be extremely important for collaborations in the BIM process.

I tried to learn some Python basics and to understand the IFC export and just submitted this pull request https://github.com/FreeCAD/FreeCAD/pull/4799. to improve the IFC export for slabs.
Certainly not perfect but seems to work

ifc_export_test.jpg (163.62 KiB) Viewed 2577 times

[paullee]

I tried to learn some Python basics and to understand the IFC export and just submitted this pull request https://github.com/FreeCAD/FreeCAD/pull/4799. to improve the IFC export for slabs.
Certainly not perfect but seems to work

Wow! Impressive progress !

I have not much idea about IFC at the moment. Look forward to your coming contribution !

[bernd]

you are a offical FreeCAD developer, welcome to the party https://github.com/FreeCAD/FreeCAD/comm ... or=balrobs

git commit 8ac722c1e89e