Why is there no descending section of the skeleton curve when I do the cyclic analysis of the column?

Post Reply
jiayanghnu
Posts: 10
Joined: Wed Nov 29, 2023 9:56 am

Why is there no descending section of the skeleton curve when I do the cyclic analysis of the column?

Post by jiayanghnu » Fri Apr 19, 2024 2:34 pm

Hello, I am using STKO for the cycle analysis of a reinforced concrete column. I found that when I used ASDConcrete (6p) concrete material and steel02 material, my skeleton curve did not have a descending section. Could you please help me look at my model? Any help would be greatly appreciated!
Attachments
D.column-solid-ASConcrete3D.zip
(464.45 KiB) Downloaded 19 times
微信图片_20240419223239.png
微信图片_20240419223239.png (53.07 KiB) Viewed 166 times

kesavapraba
Posts: 301
Joined: Sat Mar 28, 2020 2:25 pm

Re: Why is there no descending section of the skeleton curve when I do the cyclic analysis of the column?

Post by kesavapraba » Fri Apr 19, 2024 7:41 pm

Hi, The response does not soften since the rebar material (steel02) continually increases when the strain increases. In actual case, there will be fracture at a certain strain value (here I assumed it to be 5%, you should play it to get a good match in your cyclic curve), and the stress response has to be zero after the fracture. So, you can set a MinMax and Parallel material for Steel02 to obtain proper softening response. Please check the revised SCD file attached here and modify it accordingly.
Attachments
softening.png
softening.png (114.92 KiB) Viewed 162 times
D.column-solid-ASConcrete3D_rev.scd.zip
(458.95 KiB) Downloaded 18 times
:: With best wishes ::
Prabakaran Kesavan

jiayanghnu
Posts: 10
Joined: Wed Nov 29, 2023 9:56 am

Re: Why is there no descending section of the skeleton curve when I do the cyclic analysis of the column?

Post by jiayanghnu » Sun Apr 21, 2024 4:58 pm

kesavapraba wrote:
Fri Apr 19, 2024 7:41 pm
Hi, The response does not soften since the rebar material (steel02) continually increases when the strain increases. In actual case, there will be fracture at a certain strain value (here I assumed it to be 5%, you should play it to get a good match in your cyclic curve), and the stress response has to be zero after the fracture. So, you can set a MinMax and Parallel material for Steel02 to obtain proper softening response. Please check the revised SCD file attached here and modify it accordingly.
In addition, in my simulation, I found that when ASDConcrete (9p) and DamageTC3D were used respectively for concrete's constitutive materials, even though their parameter values were the same, hysteresis curves were very different. When ASDConcrete (9p) is used, there is no falling section of hysteresis curve, and when DamageTC3D is used, the falling section is more obvious. Is this because ASDConcrete (9p) does not consider damage, while DamageTC does? Can you explain this phenomenon?
Attachments
hysteretic curve-DamageTC3D.png
hysteretic curve-DamageTC3D.png (135.27 KiB) Viewed 136 times
DamageTC3D.png
DamageTC3D.png (54.15 KiB) Viewed 136 times
hysteretic curve-ASDConcrete(9p).png
hysteretic curve-ASDConcrete(9p).png (162.41 KiB) Viewed 136 times
微信图片_20240422005251.png
微信图片_20240422005251.png (250.6 KiB) Viewed 136 times

STKO Team
Posts: 2258
Joined: Tue Oct 29, 2019 8:45 am

Re: Why is there no descending section of the skeleton curve when I do the cyclic analysis of the column?

Post by STKO Team » Mon Apr 22, 2024 8:53 am

In addition, in my simulation, I found that when ASDConcrete (9p) and DamageTC3D were used respectively for concrete's constitutive materials, even though their parameter values were the same,
The DamageTC3D tends to overestimate damage in cyclic analysis.

Note that the cyclic damage you see in the experimental test is due to multiple effects you may want to investigate.
First check steel slip and fracturing

Also, you should use a finer mesh for concrete. And the mesh for embedded rebars should be at least equal to the concrete or smaller, but not larger.

Finally, do not apply a displacement only on one edge, otherwise during the right-disp of the cycle it will pull your model, and since there you have nonlinear concrete, it may fracture in tension.
Apply a disp to the whole perimeter

Try first these modification with a monotonic test and then do the cyclic.

Post Reply