CBFEM for steel connections

About the development of the FEM module/workbench.

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ebrahim raeyat
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CBFEM for steel connections

Postby ebrahim raeyat » Sun Jan 12, 2020 9:14 pm

Hello every one and @bernd

I want to write a software for analyse and design of base plate in freecad. I searched almost of FEM topic in freecad forum. for concrete element, pre/post tension concrete, rebar, contact elements and so on, all so i model base plate with 3d element and shell element. recently i found that IDEA STATICA software use CBFEM method for analyse and design of steel connection. i want to know:
I must use CBFEM method or i can only use FEM method with shell element in freecad? and basically what is different between CBFEM and FEM?!

3d_baseplate.jpg
3d_baseplate.jpg (106.89 KiB) Viewed 589 times
2d_baseplate.jpg
2d_baseplate.jpg (95.49 KiB) Viewed 589 times
these are first model that i have been try to examine freecad mesh generation, in absence of concrete and anchor bolts or stiffeners.

this page describe the CBFEM element for analysing:

https://www.cbfem.com/about-cbfem

Code: Select all

CBFEM analysis model

Before the analysis starts, the connection CBFEM model is automatically generated. It consists of plates, bolts, anchors and welds. All plates are meshed with shell elements. Bolts and anchors are represented by special nonlinear springs and welds are discretized and modeled as special constrains enabling the stress redistribution due to their plastification.
thschrader
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Re: CBFEM for steel connections

Postby thschrader » Mon Jan 13, 2020 5:10 pm

ebrahim raeyat wrote:
Sun Jan 12, 2020 9:14 pm
I must use CBFEM method or i can only use FEM method with shell element in freecad? and basically what is different between CBFEM and FEM?!
We dont use the component method at work. It is only useful for simple 2D-connections, for 3D-joints it is too much work.
IDEA-statica mixed the analytical component method and FEM in the programm as described in your link.
We had the idea to buy it. But: idea-statica uses a plastic material curve, the limiting design factor of
a steel joint calculated with idea is the strain, not the stress (which never cant exceed the yield-stress per definition...)
But plastic deformation means remaining deformation, and thats not what we want.
So we still design our parts for acceptable stress. :)
Using 2D-elements is interesting, safes computation time.
Pic: flange with 2D-elemnts and 3D-output option.
flange.JPG
flange.JPG (32 KiB) Viewed 536 times
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ebrahim raeyat
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Re: CBFEM for steel connections

Postby ebrahim raeyat » Mon Jan 13, 2020 8:36 pm

thschrader wrote:
Mon Jan 13, 2020 5:10 pm
We dont use the component method at work. It is only useful for simple 2D-connections, for 3D-joints it is too much work.
IDEA-statica mixed the analytical component method and FEM in the programm as described in your link.
We had the idea to buy it. But: idea-statica uses a plastic material curve, the limiting design factor of
a steel joint calculated with idea is the strain, not the stress (which never cant exceed the yield-stress per definition...)
But plastic deformation means remaining deformation, and thats not what we want.
So we still design our parts for acceptable stress. :)
Using 2D-elements is interesting, safes computation time.
Thanks. but my question is that with witch element do you model all component:
1- Anchor bolts: with nonlinear springs
2- concrete: with winkler spring
3- how about for weld?

can you please provide your freecad file model?
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ebrahim raeyat
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Re: CBFEM for steel connections

Postby ebrahim raeyat » Mon Jan 13, 2020 8:48 pm

this book is useful for modelling steel connection. it describe CBFEM and how component must be modeled:

Benchmark cases for advanced design of structural steel connections

https://www.eiseko.com/public/mat/file/ ... ECTION.pdf
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Kunda1
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Re: CBFEM for steel connections

Postby Kunda1 » Mon Jan 13, 2020 11:58 pm

JFYI, there is a page on the wiki FEM Concrete with interesting links
Want to contribute back to FC? Checkout:
#lowhangingfruit | Use the Source, Luke. | How to Help FreeCAD | How to report FC bugs and features
thschrader
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Re: CBFEM for steel connections

Postby thschrader » Tue Jan 14, 2020 1:43 pm

ebrahim raeyat wrote:
Mon Jan 13, 2020 8:36 pm
Thanks. but my question is that with witch element do you model all component:
1- Anchor bolts: with nonlinear springs
2- concrete: with winkler spring
3- how about for weld?

can you please provide your freecad file model?
your questions 1-2-3:
All no, I use the FC-FEM gui straight forward, no editing of inp-file after case writing.
No special attention to the weld, because CAD-model gets too complicated.
Only a nice and easy old-fashioned linear elastic static analysis for steel parts.

Some files:
2d-flange from above, exercise only
flange_2D.FCStd
(57.78 KiB) Downloaded 8 times

Flange-segment with prestressed bolt and external loading (contact problem)
flange_segment_prestressed.FCStd
(44.19 KiB) Downloaded 12 times
The bolt is modelled "short" (zoom in) to simulate prestressing. Initial idea comes from user UR_.
Attention: use 1.order elements for meshing (see data-tab gmsh), for 2.order-elements the solver never stops.
This was a real-life problem, the controlling-engineer accepted the calculation :)

Fixing of 15-m antenna mast on concrete slab. Real life problem.
mast_fixing.FCStd
(211.7 KiB) Downloaded 10 times
I only calculated the steel-part, which was not done in the old statics.
Would be interesting to run a contact problem between plate/concrete.

comments welcome
Thomas

interesting problem done with "calculix-launcher":
https://www.youtube.com/watch?v=VA0eg0LWfWM
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bernd
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Re: CBFEM for steel connections

Postby bernd » Tue Jan 14, 2020 4:00 pm

I do go the same way as Thomas (thschrader) but sometime I use nonlinear material in FreeCAD anyway. I know there will be larger strain and thus larger deformations.

BTW: We do have one licence of idea-statica and most engineers use it. But I prefere FreeCAD FEM. It is just what I know best. Until now I could not convince other to use FreeCAD FEM. Neverless it is accected by the others for me to use it.

bernd
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ebrahim raeyat
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Re: CBFEM for steel connections

Postby ebrahim raeyat » Tue Jan 14, 2020 6:35 pm

Kunda1 wrote:
Mon Jan 13, 2020 11:58 pm
JFYI, there is a page on the wiki FEM Concrete with interesting links
yes @Kunda1, I have been study all of that link and sublinks!
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ebrahim raeyat
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Re: CBFEM for steel connections

Postby ebrahim raeyat » Tue Jan 14, 2020 7:12 pm

thschrader wrote:
Tue Jan 14, 2020 1:43 pm

comments welcome
Thomas

interesting problem done with "calculix-launcher":
https://www.youtube.com/watch?v=VA0eg0LWfWM
very thanks, I will review your useful files and this is great.
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ebrahim raeyat
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Re: CBFEM for steel connections

Postby ebrahim raeyat » Tue Jan 14, 2020 7:19 pm

bernd wrote:
Tue Jan 14, 2020 4:00 pm
I do go the same way as Thomas (thschrader) but sometime I use nonlinear material in FreeCAD anyway. I know there will be larger strain and thus larger deformations.

BTW: We do have one licence of idea-statica and most engineers use it. But I prefere FreeCAD FEM. It is just what I know best. Until now I could not convince other to use FreeCAD FEM. Neverless it is accected by the others for me to use it.

bernd
I enjoy your work, but i think in myself that who wrote the FEM workbench? are you alone @bernd?

now i understand your comment about OPENSEES solver along time ago, i think it is valuable FEM analysis software and probably i examine that for future.