MOMENTS AND SHEARS IN SHEAR WALL

[allano89]

Dear STKO team
I´m working time history analysis, but in the shear walls I can´t get the same moment and shear like I get in the ETABS. In the Etabs in one pier i get 1051406708 N-mm (105 T-m) and in STKO just 158460000 N-mm (15 T-m). By the other hand in surface elements how to get the magnitude of shear?
Please your help because I´m searching about the variation of moments and shears in the beams, columns and shear walls considering the SSI (soil structure interaction)
Please your helpe
I´ve attached the model and diferences

[STKO Team]

I´m working time history analysis, but in the shear walls I can´t get the same moment and shear like I get in the ETABS. In the Etabs in one pier i get 1051406708 N-mm (105 T-m) and in STKO just 158460000 N-mm (15 T-m)

Before checking for differences in internal forces, make sure everything else match. I see some incosistencies in your model:

• Some analysis have a penalty = 1.0e12, others 1.0e18
• In the Rayleigh Damping, you used 1 Hz and 2 Hz as the frequencies of interest... are you sure? did you have a look at the modal report to understand what frequencies you should get?

Now, there can be many sources for differences.
First make sure the modal properties are similar (periods, modes of vibrations, total mass of the structure).

Then, check the global response in terms of displacement and acceleration.
If everything match, we will have a look at the forces.


Regarding how to obtain total internal forces from shell elements:
If you want to measure them at the base, where you have the fixities, you can simply check the reactions and sum them.
Otherwise you need to integrate the globalForce results at the elements' nodes. This is not easy, but we implemented in the new version of STKO we will release soon

[allano89]

Thanks a lot
I get better results but I can´t matching 100% specially the acceleration.
Please maybe you could give me some advice thanks.
Pd I´ve attached the mistakes and displacement and acceleration

[STKO Team]

We don't have ETABs here and we cannot check why there are differences. There can be many sources.
Starts by simple things:

Did you compare modal properties?

[allano89]

Dear STKO
Thanks a lot.
Please I´ve compared between ETABS and STKO the modal results and the values almost are the same. In fact, the base shear is almos the same but the moments it doesn´t match.
Please your coment.

[STKO Team]

The moment is different because, I think, you computed just by summing the Moment Reaction at each node, isn't it?
This is not enough. The total moment with respect to the center of the wall is:
SUM(MYi) + SUM(FZi * Di) (for each node "i").
I.e., you have to sum the moments and the couple given by the forces times the distance from the center of the wall.

This is not easy to do manually.
In the next STKO version (3.2.0) there will be a dedicated tool in the post-processor.

In the meantime, I prepared a "relatively" simple TCL script that allows you to do the "Section Cut" for integrating nodal forces and moments along a Linear Cut.
Note: For simplicity, it will work only in 3D models, only for 2-node beams and 4-node shells (like in your file).
Note: It works only if you use 1 partition (instead the integrated tool in version 3.2.0 will work for every element, and for any number of partitions)


Here's your modified file:

08-MODELO EMPOTRADO 2 PISOS.zip

(446.05 KiB) Downloaded 20 times

You can create selections sets for all the Edges where you want to compute Section Cuts:

Sets.png (104.2 KiB) Viewed 1017 times

For each selection set, you can create "Regions", in order to have a TCL list of nodes for each Section Cut.
After all regions, there is a script for the Section Cuts.
In the first lines, you have the User-Parameters (i.e. settings that you can change). Have a look at the descriptions, but it should be pretty easy to understand.

SectionCutScript.png (152.8 KiB) Viewed 1017 times

Pay attention to the "cut_sides". it should be +1 if the elements are on the +X direction of the cut, or -1 otherwise:

Signs and elements.png (47.89 KiB) Viewed 1017 times

This script will generate 6 files (for the 6 components N, Vy, Vz, My, Mz, T) for each section cut in a folder called "CutFiles".
These files have the same format of the Monitor Plots, so that if you have a monitor, you will be able to see them in real-time:

IntegratedResults.png (251.41 KiB) Viewed 1017 times

[allano89]

Thanks a lot. You are so kind.
It´s very helpful. I get the almos same moments.
Now I had another problem when I model more stories or basements the result again aren´t the same. I get almos the same period and frequiencies but the shears aren´t the same and the moments even worse. I belive that how I model disp.beam column I need more elements. Please your help.
Another question please, when I model basement I don´t get the backstay effect in the shear wall, how to get it? Maybe i need to input another stiffnes for the basement´s wall?
Pd: thanks a lot foy your patience and I´ve attaacher all the information.

[STKO Team]

Regarding the difference in the modal properties
There can be many reasons for 2 different software not to match. Especially in the nonlinear range. Note that you are doing an eigenvalue analysis after a gravity analysis with nonlinear materials.
Are you sure in ETABS you do the same? Are you sure ETABS considers the tangent stiffness when doing eigenvalues?

Try doing the eigen analysis before the gravity analysis. Do you see any change?

Regarding the backstay effect
Look at the results (not only the disp or acc time history, look at the whole model). You will soon realize why:

Immagine 2022-11-21 101725.png (220.58 KiB) Viewed 1003 times

[allano89]

Thanks a lot for your help
I really apreciate all your help and advices. Right now I get almost the same result that ETABS when I model whit out basements.
Just one last question how I get the backstay effects? Because now I get deformation in the basements but in the shear wall the shears are constant in all the height and I didn´t have the backstay effects of the building. Please your help.

[STKO Team]

I think there is something missing:

Shouldn't there be a backstay diaphragm? otherwise, the base walls will move independently: The axial stiffness of the connecting beam is not enough

backstay diaphragm.png (195.92 KiB) Viewed 989 times

Also, when you merged the base walls (correct), I think you lost property assignments on columns and beams. Or is it a continuous wall? Check it

no property.png (79.58 KiB) Viewed 989 times

You should also mesh the walls. One element per face is not enough

no mesh.png (105.09 KiB) Viewed 989 times