CBFEM for steel connections

About the development of the FEM module/workbench.

Moderator: bernd

User avatar
ebrahim raeyat
Posts: 619
Joined: Sun Sep 09, 2018 7:00 pm
Location: Iran
Contact:

CBFEM for steel connections

Post by ebrahim raeyat »

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 2316 times
2d_baseplate.jpg
2d_baseplate.jpg (95.49 KiB) Viewed 2316 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
Veteran
Posts: 3129
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: CBFEM for steel connections

Post by thschrader »

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 2263 times
User avatar
ebrahim raeyat
Posts: 619
Joined: Sun Sep 09, 2018 7:00 pm
Location: Iran
Contact:

Re: CBFEM for steel connections

Post by ebrahim raeyat »

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?
User avatar
ebrahim raeyat
Posts: 619
Joined: Sun Sep 09, 2018 7:00 pm
Location: Iran
Contact:

Re: CBFEM for steel connections

Post by ebrahim raeyat »

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
User avatar
Kunda1
Veteran
Posts: 13434
Joined: Thu Jan 05, 2017 9:03 pm

Re: CBFEM for steel connections

Post by Kunda1 »

JFYI, there is a page on the wiki FEM Concrete with interesting links
Alone you go faster. Together we go farther
Please mark thread [Solved]
Want to contribute back to FC? Checkout:
'good first issues' | Open TODOs and FIXMEs | How to Help FreeCAD | How to report Bugs
thschrader
Veteran
Posts: 3129
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: CBFEM for steel connections

Post by thschrader »

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 52 times

Flange-segment with prestressed bolt and external loading (contact problem)
flange_segment_prestressed.FCStd
(44.19 KiB) Downloaded 64 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 47 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
User avatar
bernd
Veteran
Posts: 12849
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland
Contact:

Re: CBFEM for steel connections

Post by bernd »

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
User avatar
ebrahim raeyat
Posts: 619
Joined: Sun Sep 09, 2018 7:00 pm
Location: Iran
Contact:

Re: CBFEM for steel connections

Post by ebrahim raeyat »

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!
User avatar
ebrahim raeyat
Posts: 619
Joined: Sun Sep 09, 2018 7:00 pm
Location: Iran
Contact:

Re: CBFEM for steel connections

Post by ebrahim raeyat »

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.
User avatar
ebrahim raeyat
Posts: 619
Joined: Sun Sep 09, 2018 7:00 pm
Location: Iran
Contact:

Re: CBFEM for steel connections

Post by ebrahim raeyat »

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.
Post Reply