modal analysis error

[gookki]

I want to make a model with infill walls and waist-height wall.
I have some problems with the infill wall element tool because of the interaction between the surface and truss element.
So, I just test one infill wall that don't interact with the truss. I make the model then merge the whole element. Then I have a minus value with eigen command. also, the post-process graphic that I got was horrible. I want to find what's wrong with it.


One more problem: During modeling, whenever truss or wall is merged, columns or beams disappeared. So I need to draw it again. I also want to know why this is so.

[STKO Team]

There were several errors in your model.
Here is a fixed version, check it after reading what I changed:

model_inele.zip

(223.03 KiB) Downloaded 295 times

Errors:

• 3 Lines around the infill were missing an ElementProperty, therefore your system was singular (negative eigenvalues)

  

  3_lines_with_no_elem.png (75.74 KiB) Viewed 5537 times

• Some nodes at the base were missing a fix

  

  2 cols no fix.png (87.62 KiB) Viewed 5537 times

• An extra node was wrongly fixed as master of the diaphragm

  

  extra_node_fixed.png (91.89 KiB) Viewed 5537 times

• Some columns were drawn from top-to-bottom. You declared the column load in local coordinates, so the Wx would follow the dir_x of the lines. But on those wrongly oriented columns, the load will point upward. I just changed the load from local to global

  

  wrong_col_orient.png (315.07 KiB) Viewed 5537 times

• With the above-mentioned fixed, your model runs, but it will have periods of 30 seconds... There is an error in the mass. You assume a mass density for concrete of about 2.35e-5, but this is a specific weight in N-mm (equal to 23.5 kN/m^3). Your mass density should be 2.35e-9. So I scaled all your masses by a factor of 1.0e-4. Keep in mind that in N-mm the acceleration of gravity is 9806 mm/s^2.
  With this, your periods lower to about 0.3 secs.
• Same for loads, I think they where 1e4 time larger.. so I scaled them by 1.0e-4.
• On trusses you cannot use eleLoad, I changed it to EdgeForce
• I replaced the old TCL script for modal analysis to the new modalProperties command that we added recently to OpenSees

[gookki]

Thanks for you help, a lot of progress has been made.
but I have still one more problem.
I want to make infill wall element inside of model.
when I draw the wall with interaction as shown in the figure, it will be triangle even I set quadra.

Is there a modeling method for this situation? Or should I add the tcl code myself?

[marafini.f]

Dear gokki,
The faces at the ground level of your structure are quadrangular but with 5 edges, and 5 vertices. If you assign size 1 to the edge seed you will never have a quadrangular mesh, because that additional node needs to be considered by your mesh.
If you want to model your infill as a truss, we made a webinar about it, number #11 https://asdeasoft.net/?webinar, you can check it out to learn how to use such elements. However, you will need to have square faces to apply the truss to simulate the infill walls, so you will need to either remove the diagonal element or divide your faces in two parts.
Let us know how it goes.
Best,
Francesca =)

[STKO Team]

Adding to what Francesca already said,
you have only 1 option to solve this issue if you still want to use the automation of the infill-wall element.

We recently added the ASDEmbeddedNodeElement under the Condition->MP models.

This condition can be used to force a node to be attached to an element, even if the two are not physically connected. It will be the topic of our next e-learning course (June).

If you attach your model we can show you how to use it.

[gookki]

Thank you for your answer.
In fact, I was considering adding elements directly to the code. However, I wonder how to use ASDembeddedNodeElement.
so I want you to briefly show me how the function is applied.
Thank you very much for your help.

[STKO Team]

Dear gookki,
I just realized that using the ASDEmbeddedNodeElement in this case would require too much work.
Instead I adopted the other solution:

• I detached the walls (Faces) from the frame (Edges). In this way the walls do not intersect with the diagonal low trusses, and therefore they can be meshed with a single quad element.
• I added an EDOF condition between the Frame and the Walls in all 6 DOFs to restore continuity
• I had to change the constraint handler to Penalty, because now the EDOF will be in conflict with the rigid diaphragm using the transformation method.
• For the same reason, I had to put a fake analysis (0 steps, without the wipeAnalysis) before the eigen, otherwise the eigen (by default) will choose the transformation method.

Please make sure I re-applied all masses and loads correctly after changing your model

test.zip

(259.28 KiB) Downloaded 303 times

[[email protected]]

Dear STKO team,
I want to perform a time history analysis on the Cold-formed steel 2-story building. The sections are built-up sections that are modeled as section fiber. The acceleration is applied and analysis is carried out in STKO but the results that I got from SAP2000 are not at all matching with STKO analysis.
To rectify the problem I tried to perform the Modal Analysis but, the first two-mode themselves are showing wrong results. The natural frequencies are as shown in the attachment which is wrong.
I am attaching the .scd file kindly help me through this.

Thank you!

[STKO Team]

There were 2 errors that lead to invalid eiegvalues (NAN):

• All your fiberSection have GJ = 0. This makes your model singular (almost because they add a very small value). I solved it by assigning to each section , GJ = G(steel)*J(of your cross sections)
• Since you split your rigid diaphragm in 3 per floor, there are some nodes that belong to multiple rigidDiaphragm, and this is not supported by the Transformation constraint handler. Since the eigen analysis by default uses the Transformation, I had to add a "fake" analysis (0 steps) with the Penalty method, and without the "wipeAnalysis" at the end.
• I moved the eigen command at the beginning, but feel free to put it back at the end.

trail_4.zip

(267.24 KiB) Downloaded 321 times