Panel cuts in walls for moment and shear force

[Anonymous]

Hi, all,

I'm in need of help with regards to obtaining correct moments and shear forces in shear walls in a building I'm modeling. The aim is to compare with my manual calculations.

1) I define panel cuts with "Between 2 points, parallel to axis" and use axis Y. 

I then use "Local direction" and Moments M - Myy. 

This does not seem to yield the correct (integral) values. Neither does xx or xy. Any idea why? 

2) The second alternative I learned from Rafael and probably just as good is to use the reduced forces and moments. These numbers does not seem too far off from my hand calculations. Certainly a deviation, but in the ballpark.

I do however notice that there's some issues with the sign convention. Is this because these moments are balancing the outer moments? Could I simply ignore the sign convention here?

3) Is it possible to create a diagram similar to the one I'm attaching for both shear and moments?

Thanks very much in advance! 🙂

[Mohammed_Ata]

Kindly, attach us the model file.

[Anonymous]

Hi, Mohammed,

Appreciate it, but the model file is 150 mb. I think that makes it hard?

Alternatively, I'd had to create a new similar and simplified model with only one load case. 

[Mohammed_Ata]

If your file is too large! you can take the following steps to save it in few megabytes

1- Analysis >> meshing >> local mesh deleting 

2- File >> save as >> *rtd without results

I have tried more and more and convert 100mb to 2mb, try it and attach us the model, if possible

[Rafacascudo]

1_ Yes you can have shear and moment diagrams like that . You just have to set the stories (Geometry/stories) and then which panels form the core wall (Geometry/additional atributes/Core walls) . Results for core walls on Results/diagrams for buildings.

You will get intermediate values if you divide it on more stories/panels

2- As I said in another thread , you will not get in-plane moments for a panel through the "integral" value of the panel cut . But you can get the out of plane moment for that cut using "local direction of the cut" and Mxx integral value .

   For shear , good news . You can get in-plane and out of plane values through the integral value.

For out of plane shear use "local direction of the cut " and Qxx integral value.

For in-plane shear also use "local direction of the cut " and Nxy integral value

Easiest way , without having to bother with directions of the cut and which force to choose is to get the results through "Reduced forces" and "Reduced moments" on panel cuts dialog window ,cuts tab.

But, important , Result values (Fxyz , Mxyz) will always be in relation to global coordinate system!!!!!

So ,Easiest , Yes , but only if your panels lay on main global planes XY ,YZ or XZ.

[Artur.Kosakowski]

Thank you Rafael

[Anonymous]

Rafael,

You're a saint! Thank you very much for this. I'm learning a lot. Will try to implement it in a short bit.

Finally, could you give a comment on the sign convention that I asked about?

Also, why do I get moments on the top cut? Is it a moment due to the slab/wall connection? I think I modeled a release there, if not, I suppose I need to? I expect shear force at the top cut, but not moments. At least not that much. 

But maybe my poor statics skills are haunting me... 🙂 

[Rafacascudo]

I don´t really bother about sign convention .If I´m in doubt ,I usually check the deformations. But it seems that for Reduced results it is according to global coordinates axis directions.

What moments in top cut? Show us

[Anonymous]

Hi,

Thanks.

I think I figured out the sign convention upon seeing the moment diagram. I just don't quite understand why it is so. My slabs are supposed to be pinned, so I wouldn't expect moments there. My hand calculations show zero moments on the top floor as per the picture attached earlier.

I tried comparing the core wall values as shown in the diagram with the panel cut values. There seem to be some small differences. Probably due to some difference in calculation and mass center in the core walls? Please see attached picture.

The easiest thing would probably be to find forces directly from the moment diagram. Then I won't have to spend time on defining cuts. But not sure which values would be most correct of the panel cuts or core walls result?

Regards and thanks.

EDIT: Is there also some easy way to hide structural elements to obtain ONLY moment/shear diagrams? I tried now using deformations and turning off panel interiors. That seemed to work. But I still got the supports. I'm sure there's some other way.

[Rafacascudo]

1-Hard to say without having your model but if you have a slab attached along the top edge of the highest panel then that small moment is correct. The pinned release would be efective for the out of plane moment. But what is shown in your figure is the in plane moment of the core wall.
If the shear between the top core wall panel and the slab is not released ( and it shouldn't !) Then this connection would be enough to prevent free rotation of the top panel top edge and then that small moment would be correct.
But again, that's without seeing your model.

2-I think moments and forces for the core walls and panel cuts are achieved in the same way , through integration. But maybe for core walls integration is done in a position slightly different from the ones of panel cuts. Maybe Artur ,Rafal or Pawel can clarify this difference.
Probably if you refine the core wall mesh the differences will be smaller

3- for better visualization , select what you need and open in another window. You can turn the support symbols on View/display

[Anonymous]

Hi, Rafael,

Thanks.

I applied a linear release on top wall between the wall panel and top slab. Rx release. It did seem to reduce the moment slightly and added an instability, but the moment is still there. 

Showing the model in a picture with lateral wind loads applied. Also showing my hand calculated moment diagram for a side by side comparison. As you can see, I have zero moment on top and a continuous tensile side.

In Robot, I get compression on the upper top. For all I know, this might be more correct. That, or I have some model error in Robot.

Thanks for those other tips. It helped. 🙂

Best regards.

[Anonymous]

With regards to panel cuts.

Ain't it easier to simply use 

Results --> Advanced --> Reduced results for panels

?

Is there any difference between these cuts and panel cuts? 

On the last cut at floor level the values are similar on the walls shown earlier, but I seem to get different values on panel cuts at a higher height. 

[Rafacascudo]

the difference is that you get only 3 cuts in one direction for each panel . 2 on the edges and one in the middle

[Anonymous]

Yes. 

And those cuts are fine with me.

But the results should be the same?

[Rafacascudo]

should be if you manage to set your cut in the exact same position as Robot , which I don´t know where it is

[Artur.Kosakowski]

Very close to the panel edge but I don't remember the exact distance 

[Anonymous]

Panel cuts VS Reduced results for panels.

There does seem to be differences. The bottom moment at the foundation is basically the same, but there are differences at higher levels.

Attaching a picture.

[Artur.Kosakowski · Accepted solution]

The answer for this post is available in this topic:

https://forums.autodesk.com/t5/robot-structural-analysis-forum/reduced-results-for-panels-vs-manual-...