Grasshopper

generative modeling for Rhino

# Gridshell Form Finding

Hi everybody,

I'm part of a team investigating kangaroo's application to optimize form finding strategies in gridshell design. We've gotten fairly comfortable with the process of creating catenary meshes through the placement of anchor points. Is there a method of creating anchor boundary conditions through a curve versus a series of points? I've had limited success through iterating anchor point densities, but it's merely imitating a true boundary condition.

Thanks!

Tags: Gridshell, catenary

Views: 1910

### Replies to This Discussion

Hi Ben,

It's not included in 0.044, but I'll definitely be including a 'ConstrainToCurve' function in the next version.

I can see how this would be quite useful for this sort of thing.

Daniel

Hay ben. Iv been playing around with Kangaroo for a while now trying to work out the form finding. I cam up with this to select the outer points of a mesh as anchor points. I dont know if it helps or not.

Also i was wondering if anyone out there knows how to determin at what point you should stop the form finding. As in how do i know if my gridshell should be realy shallow or realy deep. I have an equation related to curvature at seporate points but i dont know how to determin this in grasshopper.

If anyone could help it would be great.

Regards,

Mike.

Hi Michael

Your question about optimal form for gridshells relates to the potential of using kangaroo parametrically for this. The structural capacity of a gridshell is partly dependent upon the strength of the lath components in the overall assembly. If you can analyze the maximum curvature circle allowed by the material, you might be able to parametrically relate the formal relaxation constraints to this value. This is reducing the complexity of gridshell design to a simplified idealization condition, but might be a place to start the computational research.

Ben

Hello Mike,

In response to your question about how shallow or deep a grid shell needs to be: a 'deeper' (more curved) grid shell is in general structurally more efficient. The interesting thing about shells is that less material also makes it more efficient in carrying loads.

In addition, the answer to your question depends on the way you want to build the grid shell. For example if you want to make a flat grid first which is bent into shape at site (as was done for the Mannheim grid shell and several others) you need to work out how much bending the laths can have before they will break, this will give an upper limit for how deep it can actually be.

In my thesis I worked on some of these problems for a timber grid shell, although I didn't use grasshopper for this so I can't really help you with that.

regards,

Maarten

Hey guys,

I am working around the investigation of the form finding shell and I am pretty new with Kangaroo. Would someone be able to post a definition for further understanding or a more simple direction on how i could digitally form it?

Thank you

Natasa

like this...? basic kangaroo hanging model from a rhino surface.

Attachments:

Thank you Oliver...That is great help but how would you be able to select points from the surface more than the ones in the edges??

Hello,

Please correct me if I'm wrong becuase I'm having a hard time getting my head around the physics of this but... does the weight of the material not influence the shape of the gridshell? That would be the case for the inverse catenary form would it not, which would then also be the case for the optimum gridshell?

Also a slight deviation from the original question but nevertheless relevant... Why are the gridshells always compression/hogging shaped? This of course makes sense for materials like concrete (the classic Heinz Isler shells) but for steel (equally as good in tension) why not have hanging structures? I don't mean with cables, I mean actual steel members for example with glass and steel. This would be a refreshing change would it not? Also it would probably eliminate any buckling problems that may exist with arched shells?

I would really appreciate some thoughts on both topics, feel free to tell me I'm completely wrong on both accounts :)

Cheers,

Sam

I’m thinking the same as Sam hear I think. If you are to make it more curved you could go on forever but for all that you are adding more material so essentially making it less efficient. But if you have less material then your curve is lighter but also flatter so wont be as efficient will it?

Therefore is there not a point where you have a balance between material and curvature?

I know that there is a method (GSA formfinding) where you apply your loads to the gridshell, measure the vertical displacements of each node, and then move each node the opposite direction by the same magnitude and keep repeating until the displacements are so small. This is apparently the optimal shape but I don’t know how to run an iterative process in Grasshopper of how to reverse the loads.

The method I am looking at is to use a curvature that the material could take to achieve the same thing. How then do you find the curvature of a point. Also say that your perimeter/ restraint points aren’t circular, like the square given above, the curvature at a single point will vary depending on which direction you “face”. Thus you will want to measure the largest curvature.

Also at Natasa, maybe someone els would be able to help you out on that point but as far as I know (haven’t looked at grasshopper for a few months) you can pick individual points to act as a fixity points.

Hi Ben,

I just started to work on the form finding of gridshells using Kangroo. I would be appreciated if you could help me from where should I start. Have you come up with any grasshopper definition for that?

THanks

Nick

Hi Ben,

I have another question, in your projects have you started from a flat grid for form finding of the gridshell or you have already had a free form surface and applied a grid on that?

I am not sure if I have to project a 2 dimensional grid on a free form surface and then relax it or first I have to define a grid on that surface and then relax it?

It might be a stupid question and am sorry for that!!!

Thanks a lot!

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