Etabs | Import Rhino 3D Model 1

[bookowski]

I know there's an Etabs forum but it's a ghost town over there.

Has anyone had any luck with a procedure to get a Rhino model into Etabs? I've got a very complex geometry building with lots of varying concrete walls and projections. It is fully modeled in Rhino (from the architect). I'm looking for a way to get the Rhino into Etabs rather than rebuild it from scractch. The concrete is all modeled in Rhino as open polysurface. I think etabs will only take in a dxf 3d polyface, so I'd need a way to collapse all the polysurfaces to a centerline polyface for import (I think).

Long shot but has anyone done this? @JoshPlum able to offer any insider csi tips?

 

[EZBuilding]

Every time I have tried to import any Revit model into Etabs - no matter how small - I end up spending more time chasing through instabilities due to modeling errors than if I had just built the model from scratch.

Last I looked Thorton Tomasetti's had created Konstru and it looked somewhat promising. It may be a good starting point for you.

https://konstru.com/

 

[Brad805]

The use of Rhino suggests to me there will be many complex solid volumes in the model. This will be challenging unless Rhino includes an option to create the analysis model like Tekla does.

 

[JoshPlumSE]

Long shot but has anyone done this? @JoshPlum able to offer any insider csi tips?

I have never used Rhino myself. But, I have a friend who used to do structural design of pools for a living. Occasionally, he would model the 3D surface of the pool in Rhino like you have done. Then he used a tool in Rhino itself to take that 3D surface and break it into a 3D mesh of quad elements. My recollection is that he did this because Rhino did a much better job of this than any 3D FEM package he could find. Once he did this, he would export it to DXF and then import the DXF into his FEM program.

I haven't talked to him in a few months, but if this information isn't enough let me know. I'll shoot him a text message or e-mail asking more about what his procedure in Rhino was. There might be some key words that he can give to help you figure it out more quickly.

 

[bookowski]

Last I looked Thorton Tomasetti's had created Konstru and it looked somewhat promising

Thanks. I saw this on a webinar from them a while back but forgot about it. They are doing some cool stuff at tt. I'll have a look at it but it may be a rabbit hole that takes longer to learn for this one off project (I don't see needing it in general). I expect we would have a lot of instabilities to chase down (points not merging by 0.001" etc) but that would still be faster I think.

I'll shoot him a text message or e-mail asking more about what his procedure in Rhino was

That would be helpful, or if anyone inside csi has a recommendation. I'm surprised this doesn't come up more often. The etabs manual is pretty sparse on importing full 3d models, it spends most of the discussion on importing 2d plans.

The building in question is very similar in concept to 56 Leonard St in NYC (but not as tall), lots of projecting volumes and changes to the face of building, all in concrete. We had an intial etabs model built from scratch but since then the architect keeps iterating different schemes and it takes ages to build hence my search for something faster.

 

[Brad805]

I expect the architect is trying to make it as pretty as they can with all sorts of rads, and subtle features so it renders nicely. We have translated 3D solid models from Solidworks into analysis packages, but we usually have two configurations of the solid models. One for presentation and one for analysis. The architect should be able to dumb down the model in Rhino, but the challenge is getting them to do so. In solidworks all one needs to do is suppress the features you do not need for analysis. The person creating the model needs to know how to do that as 3D solid models can be built using previous geometry. Suppressing features can cause problems if not done at the right stage of modeling.

 

[JoshPlumSE]

That would be helpful, or if anyone inside csi has a recommendation. I'm surprised this doesn't come up more often. The etabs manual is pretty sparse on importing full 3d models, it spends most of the discussion on importing 2d plans.

Well, ETABS does focus more on building type structures which typically have common floor plans that are replicated over many floors. That's the focus on most of the documentation and tutorials. I know my friend used SAP2000 and RISA as part of his process. But, he did not own a copy of ETABS. Regardless, I've got a message into him and I should hear back from him soon.... I'll let you know what he says.

 

[sticksandtriangles]

Back in the day, 2012-ish I was working on the concrete canoe at my university and wanted to import the concrete canoe surface from autocad to SAP2000.

I was able to explode the surface in autocad to a whole bunch of triangle surfaces and then import that into SAP2000 through as DXF as JoshPlum mentions.

still looks like the same help page:

[URL unfurl="true"]https://wiki.csiamerica.com/display/sap2000/Import+DXF+into+SAP2000[/url]


S&T -

http://www.re-tug.com

 

[JoshPlumSE]

I was able to explode the surface in autocad to a whole bunch of triangle surfaces and then import that into SAP2000 through as DXF as JoshPlum mentions.

Actually, it's relatively easy to mesh a 3D surface into triangle because they are guaranteed to be planar. That's what was special about Rhino being able to do it with planar Quad elements.

I should point out that for most programs, the quad element is a better and more stable formulation than the triangle. This was especially true with RISA.

 

[sticksandtriangles]

It's relatively easy to mesh a 3D surface into triangle because they are guaranteed to be planar

Good to know Josh, that makes sense, never thought about it.



S&T -

http://www.re-tug.com

 

[Trenno]

The less you need to do within ETABS the better.

Sounds like you need a grasshopper script that takes the architectural polysurfaces and finds a centreline planar surface that intersects (hopefully) with adjacent polysurfaces. There's a billion better meshers available using Rhino than the ETABS native mesher.

 

[FE_struct1]

I had a crack at doing something similar a few years ago, but between Revit and ETABS using Dynamo. I'll point out some issues you'll want to keep in mind when using any sort of tool to transfer between Rhino and ETABS:

Slab setdowns and minor penetrations - if the architect has modelled them in, they'll need to take them out/make the setdown level marry up with the floor level so as to simplify the model (unless they're large setdowns/penetrations). But - and here's the fun bit - you'll want to keep the setdown block/mesh in the model (i.e., don't join it with the rest of the floor mesh)so that it transfers to ETABS as a separate shell element. This will allow you to put in different loads in setdown areas if required.

Column to slab connectivity - This is a big one. You'll need to know how the Rhino model has modelled the connectivity and then make sure the tool you're using is correctly translating that connectivity into how you'd want it in the model. I've pasted below an image showing an example of how it is done sometimes and what issues that causes:

Wall to slab connectivity - Another big one, though similar to the one above. In my experience, walls are usually modelled as continuous, with the slabs connecting into them. This will cause a gap to appear when converting from 3D to center-line models.

Wall to wall connectivity - If you're just using center-line connectivity between walls, you'll get eccentricities between walls of different thicknesses:

This one is a tad dangerous for walls. You may be thinking that the gaps can be rectified using stiff links or displacement constraints. This would be mostly fine for slabs, but for walls this can give rise to unintended stress concentrations at these locations if you don't model/mesh them properly. This problem is exacerbated by the fact that ETABS's meshing is not very good so you really can't model it properly (I'll admit I haven't used ETABS's latest and greatest version so I might no longer be correct about ETABS's poor meshing capabilities).

Beam centerlines - Beam centerlines will need to be dragged up to the level of the slab shells in ETABS. Also, you'll need to be careful with beam sections if they're being automatically created from the model. Sometimes architects will simply model a beam as an outcropping below the slab (i.e. they will not include the slab depth in the overall beam depth) and this might not be picked up by your tool.

Cutting slabs/shells along load patch lines - This is something I used to have to do when modelling floor shells in ETABS. The idea was to manually introduce a separation in the mesh between areas with different loads. However, I believe there is now a function that allows 'load patches' to be defined such that we don't need to cut the slabs. But if the load patch function doesn't work as intended, you'll need to fall back onto this.

Removal of non-structural steelwork/awnings/canopies etc. - You'll need to get the architect to remove any such steelwork as it is not necessary for your initial model and will only complicate things.

Re available tools that can help you - others have already mentioned Konstru, but you could also have a look at Speckle. It includes connectors for both ETABS and Rhino. Also, it's open source:

https://speckle.systems/tag/etabs/

Finally, re my attempt at revit to ETAB - we did use it on one project which used flat slabs (so beams were not an issue). We ended up only taking in the slabs and columns from the architect's concrete revit model. The walls were modelled manually as the eccentricity issues were taking too much time to resolve in dynamo.

My personal recommendation would be to weigh the issues I noted against the complexity of your model and the amount of time available to you. If the model is relatively regular (e.g. same floor layout across the whole structure, no transfers) and easily 'QA'able', you could go the script route. But for large, complicated models I would thoroughly recommend modelling it in manually.