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 » Tue Mar 22, 2022 9:11 am

By increasing the fracture energy and compressive fracture energy of concrete by 10 times, I found that the obtained F-S curve does not match the test, and the change is not obvious after a large value increase. How should the parameters be adjusted appropriately?
Attachments
initial model.rar
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01.jpg
01.jpg (82.36 KiB) Viewed 1099 times

STKO Team
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Joined: Tue Oct 29, 2019 8:45 am

Re: Beam-to-Solid-Bar-Slip

Post by STKO Team » Tue Mar 22, 2022 10:01 am

Unfortunately, you are trying to simulate a very complex problem with a simplified model.

Here's the issue:
You are using a homogenous continuum model (you are assuming the concrete as a perfect homogenous material) while doing an analysis of something that requires the details of the microstructure.

The ribs will generate micro-cracks whose size is comparable to those of the aggregates in concrete. But those aggregates are not modeled.

A crude trick can be to use a mesh (in the cohesive part near the rebar) that in the X-Y plane has a larger size, something like 2x the size of aggregates.
I'm not sure it will work, but probably it should smear the crack on a larger zone.

Also, try to use hexahedral elements in that area

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

Re: Beam-to-Solid-Bar-Slip

Post by cqf_2232 » Wed Mar 23, 2022 2:15 am

Do you mean to set a larger grid size in the bond area? In addition, I made a few auxiliary lines, but I still can't generate hexahedral elements in the cylinder, how to do it?
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mesh.png
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STKO Team
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Re: Beam-to-Solid-Bar-Slip

Post by STKO Team » Mon Mar 28, 2022 10:39 am

Here you can find your model with hexa meshing:
model-DamageTC3D_hexa.zip
(517.05 KiB) Downloaded 40 times

the central part has a modified damage model with Gt and Gc increased by a factor of 6.
Here's what I obtained:
slip_hexa.png
slip_hexa.png (58.88 KiB) Viewed 1070 times

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

Re: Beam-to-Solid-Bar-Slip

Post by cqf_2232 » Sat Apr 02, 2022 4:10 am

I noticed that you replaced MultiLinear with Elastic. With the MultiLinear material, even a 20-fold increase in fracture energy did not reach the test peak. In the elastic material, only one maximum bond stress can be entered to simulate the constitutive curve similar to the test. Why is this happening?
Attachments
elastic.png
elastic.png (10.38 KiB) Viewed 1059 times
MultiLinear20x.png
MultiLinear20x.png (27.99 KiB) Viewed 1059 times

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

Post by STKO Team » Tue Apr 05, 2022 2:43 pm

I noticed that you replaced MultiLinear with Elastic.
I replaced the MultiLinear with a Linear material with the same initial stiffness because the fracture happens in the concrete. The multilinear makes sense when you use an elastic material for concrete, and you concentrate all the nonlinearities in the interface.

I think the main difference was the finite element I used. The Hexa works better here. While the Tetra was failing too earlier due to a poor stress prediction
Last edited by STKO Team on Tue Apr 19, 2022 7:38 am, edited 1 time in total.

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

Re: Beam-to-Solid-Bar-Slip

Post by cqf_2232 » Fri Apr 15, 2022 9:33 am

Hello, my rebar used fiber section. I want to extract the stress at different positions of the rebar shown in Figure 1. I extract Gauss points through fiber color map(Fig. 2). Is the operation correct?
Attachments
Fig. 1.png
Fig. 1.png (68.25 KiB) Viewed 1025 times
Fig. 2.png
Fig. 2.png (228.3 KiB) Viewed 1025 times

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

Re: Beam-to-Solid-Bar-Slip

Post by Lucy2012 » Sat Apr 16, 2022 6:09 pm

Yes "sub gauss points" from fiber plot, this is correct

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

Re: Beam-to-Solid-Bar-Slip

Post by cqf_2232 » Thu Apr 28, 2022 1:15 pm

Thank you. I still have a few questions, hope you can help me. Regarding the material damage in the post-processing interface, d+ represents tensile damage, and d- represents compressive damage. Where are the boundaries of damage display defined? In other words, when will the material be damaged?
In the two models of the 'webinar_october_interactions' course, the concrete damage of the model with rigid link develops downwards from the plastic hinge area, while the concrete of the model considering bond-slip develops upwards from the end of the steel anchorage?
Attachments
material damage.png
material damage.png (23.23 KiB) Viewed 897 times
rigid-slip.png
rigid-slip.png (733.88 KiB) Viewed 897 times

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

Post by STKO Team » Thu Apr 28, 2022 4:01 pm

Where are the boundaries of damage display defined? In other words, when will the material be damaged?
I don't understand what you mean for "boundaries of damage"
the concrete damage of the model with rigid link develops downwards from the plastic hinge area, while the concrete of the model considering bond-slip develops upwards from the end of the steel anchorage?
It makes sense. In the "perfect adherence" model, the bar in the crack at the intersection column-foot is perfectly anchored, and the crack opening pulls the bar, and the maximum stress is on top.

On the contrary, with the bar-slip, the bar in the crack slips, so the maximum stress is not there anymore. It instead concentrates at the bottom anchor, which in fact is what the anchor is supposed to do.

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