Beam-to-Solid-Bar-Slip

cqf_2232
Posts: 64
Joined: Fri Dec 10, 2021 1:00 am

Re: Beam-to-Solid-Bar-Slip

Post by cqf_2232 » Thu Mar 03, 2022 11:09 am

Some theoretical knowledge is not clear, is the fracture energy of concrete in DamageTC3D the fracture energy of plain concrete or reinforced concrete under tensile load? You said that the larger diameter of the steel bar leads to the increase of the concrete crack size and the increase of the fracture energy. Does this fracture energy refer to the fracture energy of my entire model under tensile load?

Horace Horsecollar
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Joined: Mon Mar 22, 2021 11:42 am

Re: Beam-to-Solid-Bar-Slip

Post by Horace Horsecollar » Thu Mar 03, 2022 3:53 pm

What STKO team meant is different.
The bond behavior of smooth rebars is completely different from that of ribbed rebars. If you like to model the micromechanical behavior of the ribbed rebars you need to model all the details.
Look at the picture attached. The bond of the ribbed bars is ensured with a mechanical bond thanks to the ribs. The reaction forces are inclined, while in the smooth rebars the shear reactions are parallel to the rebars and the bond is chemical.
Thus, either you change the fracture energy to simulate this mechanical bond (note the concrete is partially in compression because of the inclined reactions) or you model all the ribs and the micromechanics of the problem.
I hope this clarifies this issue, it is an interesting problem, you need to investigate the literature of the bond mechanical transfer.
Attachments
bond.png
bond.png (173.82 KiB) Viewed 886 times

cqf_2232
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Joined: Fri Dec 10, 2021 1:00 am

Re: Beam-to-Solid-Bar-Slip

Post by cqf_2232 » Fri Mar 04, 2022 1:13 am

I understand the failure mechanism of ribbed and smooth rebars. My bond-slip constitutive uses ribbed rebars in the FIP model. Shouldn’t this constitutive have already taken into account the mechanical interaction between rebar ribs and concrete?
Attachments
Column4.png
Column4.png (61.52 KiB) Viewed 884 times

Lucy2012
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Joined: Tue May 11, 2021 4:28 pm

Re: Beam-to-Solid-Bar-Slip

Post by Lucy2012 » Fri Mar 04, 2022 6:47 am

No because the fracture energy of the concrete around the rebars is modified by the ribs. In addition if you look at the picture the bond surface is larger and the reaction forces are inclined. You are not considering this in your model. In other words the concrete around the rebars is stronger and more ductile due to the ribs and the transversal confinement. If you think the confinement is increasing the effect of the mechanical bond changing the direction of the reaction forces which tend to realign parallel to the rebar and therefore more or less orthogonal to the ribs. Thus the bond law is correct, the problem is the concrete surrounding the rebar. If you set it elastic or much stronger and ductile you will see that the model works
Regards

STKO Team
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Re: Beam-to-Solid-Bar-Slip

Post by STKO Team » Fri Mar 04, 2022 9:31 am

Adding to what Lucy2021 correctly said, you are misunderstanding a basic concept:

If you create a bond-slip behavior in the interface between the beam and the concrete, you are lumping all the nonlinearity in that interface. It's fine but the concrete should be elastic (as you did with the TruncatedDP).

If instead you use a nonlinear material for concrete, and its shear strength/ductility is lower than that of the bond-slip interface, the bond-slip interface will remain elastic, while the concrete will fail before... they are like 2 springs in series, the weakest fails first.

Lucy2012
Posts: 42
Joined: Tue May 11, 2021 4:28 pm

Re: Beam-to-Solid-Bar-Slip

Post by Lucy2012 » Fri Mar 04, 2022 11:23 am

Lucy2012 not 2021!

cqf_2232
Posts: 64
Joined: Fri Dec 10, 2021 1:00 am

Re: Beam-to-Solid-Bar-Slip

Post by cqf_2232 » Sun Mar 06, 2022 10:41 am

Ok, I want to ask how to extract the stress of zero-length element after using Beam-to-Solid-Bar-Slip, I want to get the bond stress of each point. I saw on the opensees official website that Element force needs to be selected in the recorder, but I did not see zero-length elements displayed in the STKO post-processing interface. How should I do it?

Lucy2012
Posts: 42
Joined: Tue May 11, 2021 4:28 pm

Re: Beam-to-Solid-Bar-Slip

Post by Lucy2012 » Sun Mar 06, 2022 8:46 pm

Select the gauss points and plot them

cqf_2232
Posts: 64
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Re: Beam-to-Solid-Bar-Slip

Post by cqf_2232 » Mon Mar 07, 2022 9:30 am

Thank you! I want to extract the bond stress (shear stress along the global Z axis) for a zero length element. After plotting a Gauss point plot, should I choose material stress-lines or material stress-volumes? If material stress-volumes is selected, how should the stress components be selected?
Attachments
Gauss Point.png
Gauss Point.png (822.79 KiB) Viewed 871 times

STKO Team
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Re: Beam-to-Solid-Bar-Slip

Post by STKO Team » Mon Mar 07, 2022 9:34 am

want to ask how to extract the stress of zero-length element after using Beam-to-Solid-Bar-Slip
In the MPCO Recorder, ask for material.strain and material.stress

Note:
material.stress will give you the output of the Parallel material wrapper, so it will be a Force (stress * tributary area). This is because, STKO automatically puts your material (MultiLinear, stress-slip) into a Parallel material, whose factor is the tributary area of the zerolength, so we obtain the force-slip behavior.
If instead, you want the stress output, you need to ask it to the MultiLinear material inside the Parallel wrapper:
material.material.1.stress
The first material keyword if for the zeroLength. It means: record all the materials in the zero length
The second material is for the parallel material, it means: record the stress of the material inside the Paralle material
1 Is for the 1st material in the Parallel wrapper (remember that a parallel wrapper can have more than 1 materials inside). In your case, it's just 1 material.
material stress parallel.png
material stress parallel.png (53.07 KiB) Viewed 871 times

Then, in the STKO Post processor do what Lucy said:
Select the gauss points and plot them
slip gauss.png
slip gauss.png (271.54 KiB) Viewed 871 times

Finally, with the Extract chart data, you can extract data to create a Chart, or just to copy paste the Table with values...
slip data.png
slip data.png (274.94 KiB) Viewed 871 times

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