Modeling CLT

[Anonymous]

Hi all,

I'm looking to model CLT panels. I've done some searching internally (corporate) and externally (forums) and I'm finding little support in this task, so I'm hoping to get some good results from this. At the end of this thread, I'm hoping to be able to model CLT panel in Robot, such that loads can be distributed to multiple edge supports.

I understand from internal documents, where colleagues have modeled CLT in other software packages, that there may be a way to homogonize the materials in the two principle directions of the plane of the panel, and then to come up with coefficients (n1 and n2 in Panel>Thickness ... > Othotropic >material orthotropy). I'm not sure if this is this method of modeling the panel thickness will allow for analysis of all the strength and serviceability criteria.

Another possible solution is to do a user-defined material, and to manually define the stiffness matrix. This is a rather complex route, but I'm open to trying to figure it out.

If anyone has experience with either of these methods, or is also interested in figuring it out, let's chat!

Cheers

[Anonymous]

So, I would like to do some additional vibration analysis. But I've eliminated self-wt from the model because I had to fudge that thickness value. Can I still make vibration analysis work somehow? I'm thinking that you can somehow assign mass, but not have it count towards Dead Load, but now we're really talking about fudging a series of inputs, and we need to be careful.

[Artur.Kosakowski]

1. In the parameters of the modal analysis mark disregard density (you don't want to have it calculated automatically for CLT panels)

2. Convert the self-weight load case (where you have automatically calculated self-weight for all model  but CLT panels and uniform load standing for self-weight for CLT panels defined) into mass

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[Anonymous]

Great: it can be done!

I understand point 1., but point 2. was a little confusing, so I'll try and explain what I did.

Because of the thickness fudge factor, I had removed the self-weight load case and added the self-weight of the CLT panel to the Dead Load load case (so it went from 1.5kPa to 2.0kPa, because the CLT panel weight is 0.5kPa). Now, I've defined another load case (19:self-wt TO mass in the attached screenshot) and defined Self-weight -PZ of the Whole Structure on Load Case 19. Then I went into the Analysis Types > Load to Mass Conversion > and converted Load Case 19 to mass, adding it to Load Case 18 (Footfall).

Yea? 

[Artur.Kosakowski]

1. Assuming that you have a model where you have both CLT panels and 'standard' elements you should define self weight (let's say case 19) not for the whole structure but for its part only applied to selection of all object but CLT panes (or alternatively apply it to whole structure and define additional self- weight load in +Z direction applied to CLT panels only). Then you convert case 19 into mass for modal/footfall analysis

2. You define a new dead load case being CLT self-weight and you assign uniform 0.5 kPa load to CLT panels and then you convert it into mass (e.g. case 20) modal/footfall analysis.

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.

[Anonymous]

Okay, that makes sense. I guess I'm just only thinking about the modelling of the CLT elements (I'm not ambitious enough to put this panel into a whole model yet :P).

I'm new to this footfall analysis, so I'll have some research and work to verify that this analysis is working. I have no idea what the output values actually mean yet. I'll verify when I eventually get a grasp.

[Anonymous]

Would I be right to guess that much of the Material Definition box is not relevant if you define a user-defined, orthogonal thickness? Most of the stiffness properties are incorporated in the stiffness matrix, and yet in the same dialogue (New Thickness) you have to select a Material. I'm not quite sure of how these parameters are being used by Autodesk, if I'm modelling CLT like this.

Would I define a different Material if I'm loading my CLT in plane versus out of plane, in order to have RSA properly incorporate the strength values properly?

[Artur.Kosakowski]

Would I be right to guess that much of the Material Definition box is not relevant if you define a user-defined, orthogonal thickness?

Correct.

Most of the stiffness properties are incorporated in the stiffness matrix, and yet in the same dialogue (New Thickness) you have to select a Material. I'm not quite sure of how these parameters are being used by Autodesk, if I'm modelling CLT like this.

Automatic self-weight, temperature load.

Would I define a different Material if I'm loading my CLT in plane versus out of plane, in order to have RSA properly incorporate the strength values properly?

What do you need the strength values for?

[Anonymous]

I don't particularly need the strength values. But CLT strength values differ in so many different ways/directions so I don't want to find out I'm inputting a value for one direction / orientation and that Robot is using that value in some other way (( don't know how it would but...)

Anyways, that's great to know. Thanks very much!

[Artur.Kosakowski]

Robot will not use strength values for static analysis. They are needed only for code checking modules but these don't include CLT panels design. 

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.

[Anonymous]

Further Developments:

We are continuing with the development of our ability to model CLT in Robot. I have been referring to the theory presented in the StoraEnso stiffness matrix document that Artur shared very early in this thread. We have come up with a whole library of these panels, defined by the Stiffness matrices that Stora Enso lists in the stiffness matrix document. We have verified the numbers in their listing using the theoretical calcs discussed in the document.

We apply uniform loads to the panels, out of plane in a simply-supported scenario and we get the expected deflection results, i.e. the deflection matches the theoretical deflection according to 5/384 wl^4 / EI where we can calc a modified I-value considering the different cross layers.

However, when we set the model up such that we apply the loading in-plane, we cannot get the expected results. We have reviewed this extensively to make sure we have the correct model setup and the correct matrix values input, but the deflection is substantially (>40%) lower than we calculate using the simplified theoretical calculation. The traditional simplified calculation was verified using our internal spreadsheets and StoraEnso's own online "Calculatis" application (which I expect is doing the same calc as our sheet). The model we are considering has a large span-depth ratio to minimize the influence of shear effects; and we have made sure to decrease the FE size to get convergence of the deflection results in  our FEM analysis.

I might be able to share the model details with the community this week; I can share the actual model with Robot support, and would we would welcome a chat about how to either address the issue, or else feel more comfortable about the FE results. It is possible that the FE results are more appropriate than the simplified calc method, but we need to base that conclusion on the theory behind these methods.

[Anonymous]

Would it be possible to include panels rather than defining panel stiffness because each panel size will have a different matrix I guess so each panel with different thickness value will need to be defined?

Thanks.

[Anonymous]

Can you please share the model here? I am now trying to model a CLT multi-storey structure in Robot and will be very happy to see an example.

Many thanks.

[Anonymous]

What do you mean "include panels rather than defining panel stiffness"? Ultimately, someone needs to define the panel stiffness matrices. CLT is a non-standardised product, so each manufacturer's bespoke build-up, with different timber properties, will require a unique sitffness matrix.

I don't have a model to share -- the only challenge is defining the stiffness matrices. I think there's enough discussion / reference on this forum, on this thread and similar threads I've participated in, to put together the stiffness matrices.

[Anonymous]

Hi ,

What I meant is we have a bim information family for KLH CLT panels which we can use in Revit and that information has also stiffness parameters of each panel. I tried to model my structure in Revit using the BIM information and tried to export into Robot to analyze my structure but it only transferred the panel thicknesses, not the stiffness parameters. Plus, while exporting from Revit, it missed the floor panels as well. I hope you might want to check this issue so it would be very useful for us to model. 

For including CLT panels, I meant we have a database for our panels prepared to be used in DLUBAL, and I was wondering if we can incorporate the same database into Robot, so we can easily choose our elements when building a CLT structure in Robot. If you could give me your email, I can send the database for you to have a look if it is something can be incorporated into Robot.

Many thanks,

C.

[Anonymous]

I think to get the stiffness Parameters from your Revit elements into Robot Orthotropic Panels, you will need to write some API code to define the Panel Thicknesses, but I really think it's possible.