Strand 7 Model not converging

[space_structure98]

Hi Engg Community,

Hope everyone is well

I am very new here and I am new to strand 7 as well. So basically I am trying to analyze a gravity dam in strand7. I imported the 3D Model from Revit- converted it into a 2D plate mesh model. I have defined the attachments between the dam and the foundation so that the modal can act as one

I am just trying to analyze for a self Weight case to just see how the model responds, however no matter what I try and play with different property parameters the solver doesn't converge at all. I can't understand the results as well since the sub-stepping is relatively low and the results are not accurate.

Could anyone please go through the attached model and let me know what might be wrong with the model?

Thank you

 

[centondollar]

What is the non-linearity which requires "sub-stepping" (do you mean time-stepping or load-stepping?)? If it is a linear analysis, there shouldn't be an issue with solution of the global system of equations. Have you applied a sufficient amount of boundary conditions?

 

[JoshPlumSE]

I know next to nothing about Strand 7. But, I have debugged a lot of structural models in my time.

The basics are the following:

For a static analysis, the issues are always with load or stiffness. Either your load is too high or your stiffness is too low. That's it. Try applying a very very small load to your structure in only one direction at a time. Try 1 lb vertically. If that works then try 1 lb laterally. If the model cannot converge, then you have a stiffness issue. Maybe you didn't enter your boundary conditions correctly. Maybe your dimensions are wrong..... Like the column is 20,000 meters tall instead of 20,000 mm. Maybe your material properties were entered in psi when you meant to enter them in KSI.

For a dynamics model, usually the issue is with either MASS or stiffness. That's all it can be for a modal analysis. But, I won't go further because it sounded like you were probably dealing with a static solution rather than a dynamic one.

 

[space_structure98]

@centondollar and @JoshPlumSE

Thank you for your response

The sub stepping refers to the load stepping. Initially, I got an error when the load stepping interval was more, so I reduced the increment (sub-stepping) in STAAD to a favorable value.

All the boundary conditions have been set since the dam needs to get restrained for both translational and rotational components in the x-axis and that is not the problem( if it was the problem then I would have got an error stating my global stiffness matrix is singular).

As far as @JoshPlumSE questions are concerned - I haven't applied any loading. as I mentioned earlier the only load that I am considering is the self-weight since I need to see how the structure reacts under self-weight. Usually, STRAND does take into consideration a dynamic stiffness value while computing the result but I try to see whether an initial stiffness value works for this and keep you posted

 

[IDS]

If you set the plate boundary line colour to "Group" (right click the plate icon on the left of the display) it shows the blue plate boundaries more clearly, and you can see there is something wrong with the model. Point at a plate and press shift to highlight the plate edge and display element information.

I suggest fixing the plates, run Tools-Clean, then run a linear analysis with comments displayed.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[space_structure98]

Thank you

I saw the meshing is not proper and there is a slight gap between meshed elements. I tried to clean the model but unfortunately, It's not working. I tried to reexport the model from Revit by providing a 10mm gap between the surface of the Dam and the rock bed and tried to connect those surfaces through attachments (as shown in the attached pic)- this seems to be working for the moment. Hopefully that should sustain the other load configurations