## Plotting of Concrete Reinforcement Ratio

About the development of the FEM module/workbench.

Moderator: bernd

HarryvL
Posts: 1052
Joined: Sat Jan 06, 2018 7:38 pm

### Re: Plotting of Concrete Reinforcement Ratio

HarryvL wrote:
Thu May 24, 2018 4:55 am
HarryvL wrote:
Thu May 24, 2018 4:41 am
... Results look credible and in line with applied reinforcement.
Worth seeing how reinforcement ratio translates into required area of bars, but what is immediately clear from the first plot:

FreeCAD: Required Ratio_x top ~ 1.3 * Ratio_x_mid_span

Design: 4 Ø 12 at top vs. 3 Ø 12 at mid span, so indeed 1:1.3
An example of how the plots could help the designer...

Above the central support, the required reinforcement in x-direction follows from the following plot:

Thomas_Beam_Reinforcement_Central_Support.png (35.07 KiB) Viewed 430 times

The required area of steel per area of concrete (on x-section x=constant) varies over the height. This is of course not practical and the x-section needs to be divided in zones with a single reinforcement ratio. In some cases it may desirable to apply several layers of steel in such way, but in this practical example of a beam only a single layer is applied. So in this the case of one layer, the average steel area required is:

Code: Select all

``````As = Rho_av * Height_of_Zone * Width_of_Zone * Material_Factor = 0.5*0.012*200*200*1.15 = 276 mm^2

3 Ø 10 gives 237 mm^2 (insufficient)

3 Ø 12 give 340 mm^2 (sufficient)
``````
To be placed roughly near the center of gravity of the zone (~200/3 = 65mm from the top).

Similar considerations can be applied for the other locations and the other reinforcement ratios.

Again, I need to stress here that I am not a qualified concrete structural engineer, so please don't take this as professional advice, but an invitation for a discussion...
Posts: 1432
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

### Re: Plotting of Concrete Reinforcement Ratio

HarryvL wrote:
Sun May 27, 2018 9:19 pm
Again, I need to stress here that I am not a qualified concrete structural engineer, so please don't take this as professional advice, but an invitation for a discussion...
No problem.
When designing the reinforcement of concrete structures, there is no "perfect" solution.
For example, when I use my commercial software, I must define the concrete cover of the
reinforcement (which defines the position of the rebars) before running the calculation.
There are some other things to keep in mind:
German DIN manuals for concrete design uses a "gliding" safety factor between 1,75-2,1, depending on
the strain of the compressed concrete zone. And you can enable the options
"limit crack width" and/or "limit deflection", which has an influence on the total reinforcement.

Do you know the "integrate variables" filter in paraview? You can slice through the threshold plot
(positive Sxx-stresses) and use the integrate filter which gives the total force in the zone.
In my case it gives approx 120 kN. When calculating the total reinforcment including safety-factor of 1,75,
I get a total reinforcement of 4,2 cm^2. My software calculated 4,46 cm^2, fits very well.
slice.JPG (147.68 KiB) Viewed 412 times
integrate_variables.JPG (73.61 KiB) Viewed 412 times
HarryvL
Posts: 1052
Joined: Sat Jan 06, 2018 7:38 pm

### Re: Plotting of Concrete Reinforcement Ratio

Thanks Thomas. I did not apply a safety factor nor did I consider any of the other criteria you describe. I will have another look - also at the integrate filter, which sounds like a cool option.
HarryvL
Posts: 1052
Joined: Sat Jan 06, 2018 7:38 pm

### Re: Plotting of Concrete Reinforcement Ratio

Now with SF=1.75 instead of Material Factor = 1.15:

Code: Select all

``````As = Rho_av * Height_of_Zone * Width_of_Zone * Safety_Factor = 0.5*0.012*200*200*1.75 = 420 mm^2

3 Ø 12 gives 340 mm^2 (insufficient)

4 Ø 12 give 452  mm^2 (sufficient)
``````
I guess the real advantage of using FreeCAD and reinforcement ratios only becomes apparent for more complex geometries (e.g. compound shapes, floors/walls with penetrations, complex support arrangements, massive 3D, etc.) and loads (e.g. temperature loading in massive bodies, earth quake, support subsidence, etc.)
FATHI RAMMAH
Posts: 70
Joined: Sun Jul 09, 2017 7:38 pm
Contact:

### Re: Plotting of Concrete Reinforcement Ratio

HarryvL wrote:
Mon May 28, 2018 9:31 am
Now with SF=1.75 instead of Material Factor = 1.15:

Code: Select all

``````As = Rho_av * Height_of_Zone * Width_of_Zone * Safety_Factor = 0.5*0.012*200*200*1.75 = 420 mm^2

3 Ø 12 gives 340 mm^2 (insufficient)

4 Ø 12 give 452  mm^2 (sufficient)
``````
I guess the real advantage of using FreeCAD and reinforcement ratios only becomes apparent for more complex geometries (e.g. compound shapes, floors/walls with penetrations, complex support arrangements, massive 3D, etc.) and loads (e.g. temperature loading in massive bodies, earth quake, support subsidence, etc.)
hello Harryvl
what is the standard reinforcement design code do you use to calculate the reinforcement ratio....thanks?
HarryvL
Posts: 1052
Joined: Sat Jan 06, 2018 7:38 pm

### Re: Plotting of Concrete Reinforcement Ratio

I use this:

http://heronjournal.nl/53-4/3.pdf

It's not related to any specific code.
FATHI RAMMAH
Posts: 70
Joined: Sun Jul 09, 2017 7:38 pm
Contact:

### Re: Plotting of Concrete Reinforcement Ratio

HarryvL wrote:
Tue May 29, 2018 11:58 am
I use this:

http://heronjournal.nl/53-4/3.pdf

It's not related to any specific code.
HarryvL
Posts: 1052
Joined: Sat Jan 06, 2018 7:38 pm

### Re: Plotting of Concrete Reinforcement Ratio

For those who want to know more about this approach in design, the following is worth reading:

https://www.researchgate.net/profile/El ... ethods.pdf
HarryvL
Posts: 1052
Joined: Sat Jan 06, 2018 7:38 pm

### Re: Plotting of Concrete Reinforcement Ratio

bernd wrote:
Fri May 25, 2018 9:55 am
try this ...

Code: Select all

``````import femmesh.meshtools
non_concrete_nodes = []

for obj in FreeCAD.ActiveDocument.Objects:
if obj.isDerivedFrom('App::MaterialObjectPython'):
if obj.Material.get('Name') != "CONCRETE":
print("NOT CONCRETE")
for ref in obj.References:
non_concrete_nodes = femmesh.meshtools.get_femnodes_by_refshape(result_mesh, ref)
else:
print("CONCRETE")
#

print(non_concrete_nodes)
``````

Code: Select all

``result_mesh = FreeCAD.ActiveDocument.Result_mesh``
is the document object but you need to pass the FemMesh and not the document object. Thus:

Code: Select all

``result_mesh = FreeCAD.ActiveDocument.Result_mesh.FemMesh``
I thought I had this issue solved, but running another test today on a mesh with a total of 113 nodes results in a list of 761 concrete nodes, i.e. femmesh.meshtools.get_femnodes_by_refshape(result_mesh, ref) == 761. Regenerating the mesh with more or less nodes makes no difference.

CON_NONCON.png (21.18 KiB) Viewed 242 times
HarryvL
Posts: 1052
Joined: Sat Jan 06, 2018 7:38 pm

### Re: Plotting of Concrete Reinforcement Ratio

I started from scratch and now get 100 concrete nodes.

By the way, I forgot to mention that 1 block is made of steel and 1 made of concrete. The interface between the two blocks contains 13 nodes and the grand total is 113. So I would expect "non_concrete_nodes = femmesh.meshtools.get_femnodes_by_refshape(result_mesh, ref)" to result in a list of 50 or 63 nodes, depending on whether or not the interface counts as steel or concrete. But it actually returns nodes 1..100.

The search continues ...