Modelling Solid with Bars

[mgaafar]

Hi, I am trying to model a precast slab with prestressed tandons inside. I was able to create the geometry, but when I started meshing, RSA does not mesh the solid with the Bars inside (no common nodes between the bars and solid blocks).

is that common or I should do something to force RSA to feel the Bars inside the solid volumn?

Thanks

[Artur.Kosakowski]

I would try the following approach:

1. Define 'cross section' of the slab as a face of a solid

2. Define nodes at the locations of tendons in the previously defined 'cross section'

3. Mesh the 'cross section' (mesh should adapt to the defined nodes

4. Use extrude to create meshed solids

5. Select the tendon nodes in the 'cross section'

6. Use translation with drag option marked to create tendons along the slab

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[mgaafar]

Thanks Artur, it worked but if you can please clarify my findings below plus other new questions just to confirm I did it right:

1-when meshing the face, it does not show any mesh, so I assume it does that internally.

2- in order to induce prestressing force in the tendons, I applied relative dilation on bars(tendons) with negative value as it wants to shorten the beam.

3- will this method works if I start using object combinations so that it becomes complex solid with complex meshing?

Thanks

[Artur.Kosakowski · Accepted solution]

1-when meshing the face, it does not show any mesh, so I assume it does that internally.

Correct. You may create a panel instead of a face to see the meshing and then extrude it into solid

2- in order to induce prestressing force in the tendons, I applied relative dilation on bars(tendons) with negative value as it wants to shorten the beam.

I think this is correct (or apply TX temperature load to bars)

3- will this method works if I start using object combinations so that it becomes complex solid with complex meshing?

No as the combination of objects will influence meshing of the final solid. In such cases the decision how to create the model will strongly depend on the shape of the solid itself.

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[mgaafar]

Thanks again Artur, now I am facing another problem, after creating the precast slab and was able to make RSA mesh at the tendons, the model meshed nicely and ran the analysis properly. but I had to create a notch in the slab (thats what happened on site) and I wanted to see the stress concentration around the notch. I created a 3D box at the notch location and subtracted the main slab from the box and it worked fine. but  now when I meshed the solid, it took very long to mesh and the mesh is so bad and full of error.

is there a better way to properly mesh the slab? please note that the notch is now very close to the tendon and I only modeled half the slab to reduce the model size.

Thanks. 

[Artur.Kosakowski · Accepted solution]

I would do this in the following way:

1. Definition of two faces (the orange and and the grey above it)

2. Meshing of faces

3. Extrusion in 3 steps (the vertical orange line define the distances)

4. Meshing and mesh freeze

5. Deleting of the 'excessive' solid mesh elements

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[mgaafar]

So, Now the client wants to thicken the slab in a local area with a pyramid shape with some openenings  as per attached photo. It is easy to create the solid shape but it has been trying to mesh for more than 24 hours now and I do not know if the mesh will be ok or I will have to go through itterations. also Bar elements has to join to meshed nodes properly.

is there an easy/faster way to the solid meshing? Like doing it in AUTOCAD and then import it to RSA? I created the model in CAD saved it to IGS, dxf and .SAT and tried to import it hoping the solid will be meshed as per Artur post in this thread but it did not work:

https://forums.autodesk.com/t5/Autodesk-Robot-Structural/Autocad-dwg-files-import/m-p/3181550/highli...

Time is not on my side, I need an effecient and fast way to do this..please help. 

http://www.screencast.com/t/DueMivbnb

[Rafal.Gaweda]

First run with ACIS - attached

Now waiting for refined mesh.

[Rafal.Gaweda]

After some time of meshing (a few hours 😞 )  ~347000 FEs

file here: http://www.4shared.com/zip/nGFUZNqj/PC_SLAB_MODEL-test_ACIS2.html

[mgaafar]

Thanks Rafal, just for curiosity, how powerful is your computer?

and If I want to model bars inside the concrete mass (Solid) and ensure that RSA will connect the mesh noddes to the bars, is it straight forward or there is a tweek around it?

Thank you very much again for your help, much appreciated

[Rafal.Gaweda]

Thanks Rafal, just for curiosity, how powerful is your computer?

and If I want to model bars inside the concrete mass (Solid) and ensure that RSA will connect the mesh noddes to the bars, is it straight forward or there is a tweek around it?

It should work, check on first model - it has been meshed in 2 minutes ; the big one - 4h 😞

[mgaafar]

Thanks again, So it seems that the mesh snaps to the bar which is good, now last question, is there a way for this model say to refine the mesh around the notch in the slab so I can use coarse mesh else where and very find mesh around the cut in the slab to reduce the mesh time?

Thanks

[Rafal.Gaweda · Accepted solution]

Thanks again, So it seems that the mesh snaps to the bar which is good, 

I am afraid it will not 😞 You have to connect it somehow by your own - maybe rigid links.

[mgaafar]

So I increased the mesh size from 50mm to 20mm, and the computer is still meshing since Friday afternoon (4 continuous days until now) and the screen is white and saying "not responding" does this means that the program crashed or still running in the back ground. (knowing that when I open task manager, the CPU is at 13% and memory at 4,283,272k for ROBOT)?

[Rafal.Gaweda · Accepted solution]

So I guess thsi is the solution :

http://www.autodesk.com/products/autodesk-simulation-family/features/simulation-mechanical

[mgaafar]

Rafal, I downloaded the trial version and it meshed the whole slab with 20mm mesh size in less than a minute!!!!!

I really think the solid meshing engine of RSA or whatever causing this to be that slow should be fixed.

Thanks anyway for your help on that topic. really appreciate it.