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

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balrobs
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[IFC Export] Problems with IFC (structural view) export/import

Postby balrobs » Tue Jan 12, 2021 6:42 pm

Hello everybody!
Today I tried to model a simple structure with FreeCad (latest Win-Conda build) and to export it as IFC (structural view) in order to after read it in with RFEM (proprietary structural analysis software) and process it further.
This is my test model:
Test_IFC_struc_export_01.jpg
Test_IFC_struc_export_01.jpg (55.73 KiB) Viewed 649 times
Test_IFC_struc_export_01.FCStd
(36.98 KiB) Downloaded 9 times
and this is my resulting IFC output file:
Test_IFC_struc_export_01.ifc
(4.24 KiB) Downloaded 8 times
Unfortunately importing this file to RFEM leads to a quite useless result:
Test_IFC_struc_export_02.jpg
Test_IFC_struc_export_02.jpg (51.47 KiB) Viewed 649 times
As you can see the wall is totaly missing, columns are recognized as members but have a *section type property*== unknown and there is no planar element for the slab but three non-closed members with also *section type property*== unknown.
Is this behavior due to the fact that the IFC exporter still needs to be improved or is it me who is doing something wrong?
Thanks in advance for your help!

PS:
I also tried to repair the broken model in RFEM, re-export to IFC and re-import to FreeCAD. Here is the result:
results.png
results.png (504.4 KiB) Viewed 649 times
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bernd
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Re: [IFC Export] Problems with IFC (structural view) export/import

Postby bernd » Tue Jan 12, 2021 6:59 pm

I do not know about the export out of FreeCAD. Never trid this. In IFC++ you can view structural analysis view to check the export.

As fir the import this should work, but I nevet got hands on a file exported from RFEM. Would you share this IFC?
balrobs
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Re: [IFC Export] Problems with IFC (structural view) export/import

Postby balrobs » Tue Jan 12, 2021 7:28 pm

bernd wrote:
Tue Jan 12, 2021 6:59 pm
I do not know about the export out of FreeCAD. Never trid this. In IFC++ you can view structural analysis view to check the export.

As fir the import this should work, but I nevet got hands on a file exported from RFEM. Would you share this IFC?
Thank you @Bernd for your answer.
In *Preferences->Import-Export->IFC-Export* you can choose *Export Type=Structural Analysis*. This should allow you to export IFC structural view of your structure ... at least that was my assumption.
Tomorrow back on my Windows machine I will try to open it in IFC++ and report back.
In the meantime here is the RFEM-generated IFC-file:
Test_IFC_struc_export_02.ifc
(21.12 KiB) Downloaded 8 times
Cheers!
balrobs
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Re: [IFC Export] Problems with IFC (structural view) export/import

Postby balrobs » Wed Jan 13, 2021 11:06 am

Importing Test_IFC_struc_export_01.ifc which was generated by Freecad with IFC++ gives a result similar to RFEM.
Test_IFC_struc_export_02a.jpg
Test_IFC_struc_export_02a.jpg (46.41 KiB) Viewed 561 times
I'm going to experiment a little with the export options in FreeCad but at first sight it seems like the export function doesn't work very well at this moment.
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bernd
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Re: [IFC Export] Problems with IFC (structural view) export/import

Postby bernd » Wed Jan 13, 2021 7:30 pm

You are right in the regard of export.

FYI:
import was implemented by me and I use it from time to time. It should work quite well for geometry and meshes. Export was implemented by yorik and I have not used it at all. May be once or twice for playing around.

export:
I might be wrong, but AFIK SurfaceMember are not yet supported. Means no shell elements like slabs and walls.
Furthermore you need to move the structural axis from the FreeCAD Arch object in a way the ends fit together. The stuctural axis is what is exported eventually.

You might search the forum. There are less than ten topics about these structural axis.
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johnwang
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Re: [IFC Export] Problems with IFC (structural view) export/import

Postby johnwang » Wed Jan 13, 2021 9:44 pm

hfc series CAE workbenches for FreeCAD (hfcNastran95, hfcMystran, hfcFrame3DD, hfcSU2 and more)
balrobs
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Re: [IFC Export] Problems with IFC (structural view) export/import

Postby balrobs » Thu Jan 14, 2021 10:43 am

Thank you @johnwang for the link :D
bernd wrote:
Wed Jan 13, 2021 7:30 pm
export:
I might be wrong, but AFIK SurfaceMember are not yet supported. Means no shell elements like slabs and walls.
Furthermore you need to move the structural axis from the FreeCAD Arch object in a way the ends fit together. The stuctural axis is what is exported eventually.
You are right. 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 :cry:
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.

Edit:
PS: Just noticed that the StructuralCurveMember generated for slabs aren't on the structural mid plane but at the lower surface (maybe the plane of the slab BaseObject?).
Test_IFC_3_storeys.jpg
Test_IFC_3_storeys.jpg (185.17 KiB) Viewed 367 times
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yorik
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Re: [IFC Export] Problems with IFC (structural view) export/import

Postby yorik » Thu Jan 14, 2021 12:49 pm

I see two problems here: 1) the slabs loops are open and 2) sometimes wrongly placed.

Basically any Arch Structural object in FreeCAD has a Nodes property (that you can show in the 3D view). That is what is exported to structural IFC.
This Nodes property is a simple sequence of 3D vectors. For a column or beam, it's just two points for start and end. For slabs, they define the points of a polyline. When editing a structural element, you have a couple of simple tools to edit those nodes, but it should be extended more.

In any case I would try 1) to set the nodes property manually, just to see if by doing so your file gets correctly exported, and 2) maybe identify what kind of UI tools would be useful to work better with those nodes
balrobs
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Re: [IFC Export] Problems with IFC (structural view) export/import

Postby balrobs » Thu Jan 14, 2021 2:36 pm

yorik wrote:
Thu Jan 14, 2021 12:49 pm
I see two problems here: 1) the slabs loops are open and 2) sometimes wrongly placed.

Basically any Arch Structural object in FreeCAD has a Nodes property (that you can show in the 3D view). That is what is exported to structural IFC.
This Nodes property is a simple sequence of 3D vectors. For a column or beam, it's just two points for start and end. For slabs, they define the points of a polyline. When editing a structural element, you have a couple of simple tools to edit those nodes, but it should be extended more.

In any case I would try 1) to set the nodes property manually, just to see if by doing so your file gets correctly exported, and 2) maybe identify what kind of UI tools would be useful to work better with those nodes
Thanks @yorik for your appreciated reply and your detailed explanation. Now everything makes a lot more sense :D
Following your advice I set the node properties manually this way
  • for the slabs I used the parameter *NodesOffset* to bring nodes on the structural mid plane. This operation is straight forward an therfore I see no need for an aditional GUI tool here.
  • as a workaround for the open slab loops I added another node with equal coordinates to the first one. IMO this operation is very tedious and the IFC exporter should be made smart enough to avoid the need of this action.
  • to manipulate the node coordinates of the single columns I changed their start and end values column after column. This is a very repetitive action and could be accelerated a lot with an adition GUI tool. Maybe by selecting multiple columns and then be able to give their start or end nodes the same z-values.
So I managed to come to this result:
Test_IFC_3_storeys_01.jpg
Test_IFC_3_storeys_01.jpg (258.6 KiB) Viewed 311 times
Being able in the future to export additionally member section properties and materials would be a wonderfull thing.
Thank you all again for such a great software!
balrobs
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Re: [IFC Export] Problems with IFC (structural view) export/import

Postby balrobs » Thu Jan 14, 2021 3:12 pm

yorik wrote:
Thu Jan 14, 2021 12:49 pm
Basically any Arch Structural object in FreeCAD has a Nodes property (that you can show in the 3D view). That is what is exported to structural IFC.
I can't find this Nodes property for Arch Walls. Could this be the reason why for Walls the IFC-Exporter don't work :?: