Instability Type 3

[Anonymous]

Hi,

I have a small model with some Instabilities in the Rx direction. I have a series of planar trusses that are restrained not at every node in the lateral direction. The results make sense and I'm sure I can just ignore this instability, though it's never desireable to be running a model with Instabilities. 

Any tips to get rid of it?

Model is attached.

Ben.

[Artur.Kosakowski · Accepted solution]

I have selected model and run intersection. Lokking at the bars tabkle I noticed some very short bars. Looking at their nodes and the origibnal model I can see that you missed some snaps.

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[Artur.Kosakowski · Accepted solution]

Corrected model. I have used the detailed corerction to these planes.

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[fmproiect]

Can somebody please tell me why do i get instability. I have attached the structure. Thanks.

[Artur.Kosakowski]

There is too many releases and linear releases for easy detection of the cause of the instability. I have re-meshed your model to have more regular surface elements and deleted RX releases as well as checked for short bar elements and these are not the reasons for it. I think that you should look at the deformations of X bracings at the roof plane but apart of that at  the first glance I can't see any other strange looking results.

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[fmproiect]

I don't understand why "too many". It should be correct. It is precast concrete structure. So every beam is pinned-pinned and the floor si made out of Hollow core sla so pinned on edges.
Which Rx realese did u delete? I also don`t understand the deformation of the x bracing in the roof plan. From where that wierd deformation? Thank you a lot for trying to help me. I have this problem with instabilities from such a long time. I also usually use truss bars for the x bracing and the instability disapears but in this case it does not :).

[Artur.Kosakowski]

I wrote: There is too many releases and linear releases for easy detection of the cause of the instability and I did not wrote that there are too many of them so they cause the instability 

Which Rx realese did u delete?

I removed them from the releases labels you used in the project.

I also don`t understand the deformation of the x bracing in the roof plan. From where that wierd deformation?

What about the self weight for a bar with such span? See the attached picture.

If you want to search deeper you may delete all linear releases (no instability) and apply them in sequences on selected panels only. 

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[fmproiect]

Hi again. I did delete elements and in the end i got to this structure. I got a bigger error now.

[Artur.Kosakowski]

You should not delete them as you need them to reduce horizontal displacements of the structure but as they are fi25 mm bars they should neither be intended to transfer bending nor compression. In other word they should be defined as tension only bars.

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[Anonymous]

Hi

I am doing a structural analysis of an individual steel module which is used for modular building project. I modeled this module with all its elements (floor and ceiling joists, wall studs etc.), applied loads in Revit structure 2016 and exported it to Robot structure analysis 2017 for structural analysis purpose. But during the analysis, it gave me some warnings as shown in attached pictures. I also attached the robot file. It is really appreciates if you can help me. I want to solve these warnings but I do not know what I should do. Thanks in advance 

[Artur.Kosakowski]

Please watch the recordings of webinars 10, 1 and 2 from http://forums.autodesk.com/t5/robot-structural-analysis/robot-structural-analysis-webinars/td-p/5523...

I have corrected the model using the detailed correction to defined structural axes so that bars are in the planes of walls.

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[Anonymous]

Thank u so much for your help

Could u please tell me what you corrected in my model? Can I correct the model in Revit first and export it into Robot? I have another model that is a wooden structure which has the same issues. I attached the Robot file for you in this message. Could u please see my model and correct the issues like what you did for my previous model? Thank u so much and I look forward to hearing back from you soon about the steps that you did in my first model as well as the following wooden structure model. Thanks a lot

Regards

[Artur.Kosakowski]

Please watch the webinars I indicated first as they explain how to correct models in both Robot and Revit. If there is anything that needs additional explanation then let me know. 

[Anonymous]

Ok. Thank you so much again. I will let you know if I still have some problems and questions.

Regards

[Anonymous]

Dear Mr Kosakowski
Thank u so much for your helps. I watched the videos and tried to solve the problems of the second model (by correcting its analytical model). Because of that it is much more complex than the first one, I couldn't solve all issues. Then I decided to correct my initial first model (an individual steel module) that you corrected it for me. But again I couldn't solve the instability issues. Could you please explain me how we can solve the instability problems and how you did it on my module? Thank you so much for your time.
Regards

[Artur.Kosakowski]

In the model I corrected it was enough to move bar elements to the planes of walls and re-mesh the panels. 

[Anonymous]

Dear Sir
Could u please show me how to do it? (If it's possible for you by sending me a quick video of the steps that you did on my module). I am a beginner in Robot and your guidance will help me a lot in all my future models (Whole modular building, etc). Thank u so much 

[Artur.Kosakowski]

Here you are:

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[Anonymous]

Thank you so much for your helps and recording this video for me. I am working on the second model (wooden structure) which is more complex. Actually I followed the steps you did on my first model for my second model, but it has not been completely corrected. I will try to correct all issue, and I will ask you if I cant' solve it. Thank u again for your time