Coupled shear walls with diagonal reinforcement

[farisuwais]

hi team

i have decided to utilize STKO as FE software to carry out my thesis study titled "Investigation of seismic performance
for ductile coupled shear walls". i have some questions related to modelling the shear walls and coupling beam in between.
before jumping to model the coupled shear walls, i am starting with model verification and validation by matching STKO result with experimental results. so i have chosen two specimens of coupling beams tested by Galano and vignoli as shown in the attached figure.

i need guidance whether to model the specimens as 3D solid element or as a shell element.
also for the diagonal reinforcements and the stirrups around them which approach do you recommend to use for modelling in STKO?

[STKO Team]

If you want to save time you can model it with shells.
Regarding the reinforcements, you can choose to model them as equivalent smeared layers, or physically embed them into the shell (The second option can be more accurate)
Check our webinars on RC shear walls.

Then you can choose which approach to follow based on how large are your models, and based on the level of accuracy you want.
For example, if you just need to simulate the detailed response of a specimen, you can go with embedding rebars as fiber-beam elements inside the shell.
If instead you need to model whole buildings you may want to use the simplified (smeared) apporach

[farisuwais]

Dear team

i have decided to model it as solids but i am facing convergence problems. please support as i have tried repeatedly to change the solver, mesh, elements,..etc. but i am reaching a dead end.

Coupling beam.zip

(6.74 MiB) Downloaded 5 times

[STKO Team]

There are some mistakes in your model. Let's try to fix them one by one.

• You have several floating vertices (for example geometry 125, 126, etc...). They are not attached to anything so they will generate a singular stiffness matrix. Probably they come from your CAD drawing, but if a geometry will not be used in OpenSees, delete it.
• Steel plates are not attached to the concrete volume. Again, it will generate a singularity. Please merge them, or provide an interaction between them and the concrete
• Pay attention to the unit system you are using! From the material I can see you are using N and mm, but the self weight is wrong

[farisuwais]

thanks for the reply.

after complying with the given comments, the model ran.

now i am applying the bar slip command but the analysis is not converging after the 15% progress. i tried changing the k (penalty) factor order, it had some effects on the convergence but still the model did not converge. i separated the interaction depending on the rebar size to add two bar slip conditions based on the size of rebar but the model did not run at all.

also, the analysis plot during the analysis does not show any graph. please advise.

[STKO Team]

Just move the monitor before the analysis and you will see the results.
It stops converging simply because it's failing.

[farisuwais]

thanks for the reply
i have questions related to data extraction in the post processor:
-i am trying to extract the rotation of the beam at certain points (refer to attached picture). while selecting the points and extracting the data chart, rotation will come as zeros throughout the steps. please provide the methodology to extract the rotation at the points shown in figure.

- how to extract the shear force in the beam throughout the steps?

i need to plot the rotation Vs shear force in the beam to compare the results with experiment.

[STKO Team]

1. You cannot see Rotations directly in the DOF of solids because they don't have rotation DOFs. You need to do your math.
   Compute the delta vertical displacements and use the length to compute the (infinitesimal) rotation
2. you can get shear force from the reactions

[farisuwais]

i would like to thank you for the support you have been providing me.

i failed to match STKO results with experiment so i decided to try modelling the coupling beam with 2D shell element instead of 3D solid element. i have been watching the tutorials on you website and YouTube and in all shear walls the 2d shell element models were modelled using smeered layers of concrete and rebars. i am afraid the smeared model approach won't give accurate results specially that I have diagonal reinforcements with stirrups.

the modelling approach that i am planning to consider is to model the shell elements in triangular and trapezoidal shapes to have the diagonal reinforcement edges as boundary elements and model the conventional reinforcements as smeared layers

sketch1.jpg (90.03 KiB) Viewed 297 times

i am not sure if this is the best way to have accurate results or maybe you can suggest a better way to model the reinforcements such that i will be having accurate results.

[STKO Team]

Actually, now you can "embed" rebars (made with beam elements) into solids or shells.
At the bottom of our webinar page there is a short course on RC shear walls (https://asdea.eu/software/advanced-e-learning-courses/):

embedd.png (42.48 KiB) Viewed 191 times