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Hysteresis loop's shape not matching (Abaqus output vs Experiment)

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compe_ad

Civil/Environmental
Apr 20, 2022
71
Hi everyone!

I am working on ABAQUS model which consists of a reinforced concrete wall and has a cantilevered W-shaped steel beam embedded (see attached picture). In order to make it computationally efficient, I am modeling just half of the full-size specimen. The steel beam is subjected to a cyclic shear loading whereas the wall has its base fixed. I have built the model and am trying to match the output with the experimental results. The stiffness of the connection is more or less matching, but the shape of hysteresis loop is quite different. The connection is failing at the same loading stage as that observed in the experiment. In summary, every other thing looks good but just hysteresis loops are different. When I looked more in detail, I found that results from loading and unloading branches are crossing for some cycles. I don't know what the reason for this might be. CDP is used for concrete and combined hardening is used for steel for defining plasticity.

I am defining cohesive interaction between steel beam and concrete. (Parameters for cohesive interaction that I am using are: Knn=0, Kss=Kst=32 kips/in2, nominal stress along normal direction=0, along shear1 and shear 2= 0.42 ksi, plastic displacement = 0.1 in.).

Can you please suggest me what may be the reason and where should I focus to fix these things?

Thank you in advance.

PS - I have attached pictures of model and plots.
SingleLoopComparison_wrelor.jpg
Forcevsdisplacement_qvz72g.jpg
model_lmhqde.jpg
 
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Typically that means you've got friction or clearances in your model (that plastic number?), but I am not familiar with non linear FEA models.

So, is this a quick run? Or does it take forever? If the latter build a simple model using the same damping/friction/whatever parameters and play around with them.

Although it looks odd these crossings can happen in reality, but your real result looks much more like normal damping, no friction (which tends to cause square ends). The 'softening' on centre is also typical of real systems.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
More to the point it is often sufficient to match the area in the loop=work done, rather than fine details of the wiggliness of the curves. In your case you don't have enough damping.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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