Help with figuring out how to model this structure

[Arg777]

Hi everyone, Im an architecture student and have some experience with modeling in 3d AutoCad and very minimal experience with revit and 3ds max. I need to model this structure and I'm having a tough time trying to figure out how to go about doing that.

 

It is supposed to be an outdoors performance space that is covered by this shell like structure. It's composed of concrete ribs meeting at a point but only in a semicircular shape. The webbing inbetween the ribs have catenary curved arched openings with some of those openings having a lattice structure inside. The top of this hemispheric dome is supposed to be a sort of skylight with mullion work and glass. Here are some sketches of what I had in mind:

 

Now I started to model it in 3D Cad since that's what I know best but this is a very complicated curved structure where curves dont just happen on one axis but 2 or 3. I was able to somewhat create the ribs but i have no clue how to actually create the shell webbing in between and then cut out the catenary curved arches with lattice work or the skylight component for that matter.

 

If anyone could help me out on this i'd really appreciate it! If it is easier to do in 3ds max, then I am able to do that too, but I just need some guidance. I've attatched my attempt of this model with the corresponding floorplan.

Performance test 3d.dwg

[ReMark]

The skylight could be created by slicing the ribs and webbing using an extruded arc. The SLICE command utilizing the SURFACE option would do the trick.

 

As for creating the "lattice work" affect I imagine you would have to create the required profiles, locate them properly (i.e.-relative to the curved webs), extrude them through the webs, then do a subtraction.

 

That's how I view it. If you are patient I am sure other forum members, more knowledgeable than myself, will post alternate suggestions.

[Arg777]

Thanks ill try those but I still need some more help with this. Especially the webbing because no matter how i do it, it doesn't seem to fill the space in between the ribs, either it leaves a gap or it just overshoots them completely. Anyone else have suggestions?

[ReMark]

I thought you already created the webbing and just had to trim it to fit.

[3D generator]

Catenary curves have the unique property that when suspended they are in perfect tension and when they are flipped to create an arch they are in perfect compression. This means the arch is totally self supporting just by virtue of its geometry. Gaudi was a big fan of this form finding technique.

 

True catenary (also called funicular) modeling is very challenging to achieve because it deals with the force of gravity on the geometry you’re creating. This requires a live physics engine as well as a geometry kernel working together to create the catenary curves.

 

Catenary curves can be approximated by parabolic curves but the results will not have the same structural properties.

 

http://mathforum.org/library/drmath/view/65729.html

 

This could all be boiled down to the math in a .NET script that you can run inside AutoCAD, but I doubt the results would be very interactive or intuitive. Besides, I wouldn’t have a clue how to do that anyway!

 

http://through-the-interface.typepad.com/through_the_interface/2012/01/generating-hyperbolic-geometry-on-a-poincar-disk-in-autocad-using-net.html

 

Your best bet is probably using Rhino with the free plug-ins Grasshopper and Kangaroo. Here’s a video illustrating how this modeling technique would work: http://www.grasshopper3d.com/video/kangaroo-basic-catenary-system

[Arg777]

Thanks for the reply but that is all far to complicated for what I am trying to do. I don't need to have the accurate forces or know the physics of it, this is just supposed to be more of a conceptual model if anything. Gaudi is where I get the idea to use the catenary curves and i was able to use a plugin to form them in 2D so although they may not be "true catenaries" they are close enough for what I am trying to do.

As for using rhino, I've never used that program and don't have the time to learn it so I would prefer if the solutions stayed within the bounds of AutoCad or 3ds Max.

[ReMark]

Post what you have accomplished since 19 April. We'd like to see the extent of your progress. Thanks.

[Strix]

I'm intrigued

 

What are the 'walls' made of? or is it a skylight and webbings with nothing inbetween?

Is this the effect you were aiming for?

[ReMark]

The structure is made of concrete.

[Strix]

The structure is made of concrete.

 

It is supposed to be an outdoors performance space that is covered by this shell like structure. It's composed of concrete ribs meeting at a point but only in a semicircular shape. The webbing inbetween the ribs have catenary curved arched openings with some of those openings having a lattice structure inside. The top of this hemispheric dome is supposed to be a sort of skylight with mullion work and glass.

Nope - still can't find where the material between the concrete ribs is defined (other than the top of the dome being glass)... have you two had off-forum conversation about this?

[ReMark]

What other materials do you have in mind? This is a music shell (i.e. - amphitheater).

 

We have one in our hometown constructed completely out of wood. My guess is, that if the structure was made of dissimilar materials it would adversely affect the acoustics.

[3D generator]

Sorry for the sensory overload. I tend to err on the side of too much information and sometimes I get carried away!

 

If all you want is a conceptual model and you want to do it in AutoCAD, I’d use surfaces to define the complex geometry. I’ve attached an AutoCAD file with an image underlay that will hopefully give you a starting point.

 

Isolate layer EDGE1 and you’ll see the geometry I used to create SURF1. The vertically curved arcs are extracted from your ribs using the extract edges tool. The horizontally curved arc is copied directly from your floor plan.

 

To create SURF1 I lofted to two vertically curved arcs and used the guide option. I selected the horizontally curved arc as the guide. Then I brought in your elevation image as an image underlay to get a rough idea of the size of the catenary opening and quickly created a profile. Then I 3d rotated the profile to be vertical and moved it outside of the geometry.

 

To create SURF2 I extruded the profile through SURF1. Then I trimmed SURF1 using SURF2 as the trimming surface to create the surface with the opening that’s copied to the side of the original geometry.

 

I tried to use thicken to create a solid shell that was the thickness of your floor plan wall depth but it wouldn’t work due to self intersections. I tried to offset the surface the same distance and that failed too.

 

You’ll probably have to repeat the process that I used to create the outer surface of the shell in order to create the inner surface of the shell. Then you can patch these surfaces together and hopefully use the sculpt command to convert the shell into a solid.

 

You mentioned that you created the catenary arches using a plug-in. I didn’t find them in the file so I created my own. What plug-in did you use? Thanks.

Surface.dwg

[3D generator]

I forgot to mention that you should be able to bring my file into your 3d model file by using World UCS and 0,0,0 coordinates.

[Arg777]

Well I had my final review yesterday so as you can imagine, I was extremely busy the last couple of days, but at least now im done! As for the model, I followed your instructions 3D generator and was able to create the surfaces of the webbing but had no luck in converting it into a solid so i had to just leave it like that. I was also able to create my lattice by extruding them and subtracting just like the arches. Here are some pics of the final thing:

 

 

My original idea for the performance space also included the glasswork at the top but I simply ran out of time to try to figure that out. Of course if I had more time I would keep working on it. Regardless of this, the rest of my project was great. The rest of my building was already in 3D, this was just sort of the icing on the cake. My reviewers really loved my project and only had great things to say about it, so I'm very happy about that. Anyway, just wanted to give you guys an update and thank you for all the help!

[3D generator]

Thank you for the update, Arg777. Nice work! I really like how the catenary arch lattice work came out, very impressive.

 

To complete the opening at the top I'd draw the reflected ceiling plan in 2D indicating the shape of the opening and then extrude those curves up through the canopy. Then you could just trim the canopy surfaces back to the extruded surfaces like you did with the arches. Too bad you didn't have enough time to finish, but I'm glad you still received glowing reviews!

 

I'm not surprised you had trouble converting the surfaces to a solid. The sculpt command can be very persnickety and often fails to work.

 

What plug-in did you use to create the catenary arches?

[Arg777]

Well actually it wasn't a cad plug-in. I found a ruby script for sketchup that creates all types of curves including catenary curves, so i essentially just drew a simplified version of my elevations with the catenary curves and exported it into autocad and then I was able to manipulate the scales of the different size of the arches by turning it into a block and then scaling x and y accordingly.