brhenri-mr/cem_dataset

A dataset of topology diagrams generated by the CEM framework

Datasets of structural forms

This repository contains a collection of manually-generated topology and form diagrams generated by the CEM framework.

The CEM framework generates the geometry of strut and tie models, subjected to combinations of tension and compression forces, such that they are in static equilibrium.

The motivation is to use the data herein is to build tools in the future that benefit from graph machine learning (ML) to improve form generation processes in structural and architectural design.

We look forward to hearing how you use these topologies and forms in your next graph ML research adventure!

Available datasets

• 🌉 Bridge topologies (Under construction)
• 🍕 Randomized unit circle (Coming soon)

How to add data to the bridge topologies dataset

⚠️ Warning ⚠️: Avoid using auxiliary trails when building a topology diagram unless there is no way around it!

0. Familiarize yourself with how the CEM framework works. Know what the distinctions between a topology, a form and a constrained form diagram are. Make sure you understand what the difference between a trail and a deviation edge is (hint: the former is parametrized by its signed length, and the latter by the magnitude of the force it carries), and what a trail consists of: it is a "polyline" of trail edges. The first node in the trail is an origin node, and the last one, a support node. In particular, be aware of how static equilibrium is calculated in the framework: it is "cascaded down" sequentially over the nodes of every trail, starting at every origin node, and ending at the support node. As a result, the location of the origin nodes in the topology diagram greatly restricts the geometry of the generated form. Simply put, there will be certain valid topology diagrams that will never generate the desired form (despite they are topologically valid!). Whenever unsure about the theory, you can always refer back to this journal paper.

1. Install the latest version of compas_cem Follow the installation instructions in this repo. Don't forget link the library to Rhino: we need to have the compas_cem grasshopper plugin installed!

2. Take a bridge example from the catalog stored as a pdf in under bridges/bridge_catalog.pdf in this repository and form-find it with compas_cem for grasshopper. Every example typology in the catalog is considered a unique bridge type with a unique name. Since, there is more than one way to model a type, topological versions of the same bridge type are called a family. We are interested in building parametric variations of 2d and 3d versions of the topology diagram of each family. Have a look at the next section for a more detailed explanation.

Deliverables: Data for a bridge type

To give you an example of what the folder structure of each bridge type should look like and what data files it should contain, have a look at the zermatt folder under bridges/zermatt.

Summarizing, this is what we are expecting for the folder structure:

bridge_type
|--|bridge_type.png
|--family_name
|--|--2d
|--|--|--family_name_2d.ghx
|--|--|--form_2d_1.pdf
|--|--|--form_2d_1.json
|--|--|--topology_2d_1.pdf
|--|--|--topology_2d_1.json
|--|--|--topology_2d_2.json
|--|--|--topology_2d_3.json
...
|--|--|--topology_2d_N.json
|--|--3d
|--|--|--family_name_3d.ghx
|--|--|--form_3d_1.json   
|--|--|--form_3d_1.pdf
|--|--|--topology_3d_1.pdf
|--|--|--topology_2d_1.json
|--|--|--topology_3d_2.json
|--|--|--topology_3d_3.json
...
|--|--|--topology_3d_N.json
...
|--family_name_B
...

Let's break the folder structure down:

First we choose a unique and descriptive name bridge_type for the bridge type we will work with, for example zermatt, vierendeel_truss or suspension_bridge. Then, we set a name family_name for the bridge we will be modeling. A bridge family identifies a particular topological way to model the bridge or case-specific boundary conditions. For example. zermattA and vierendeel_truss_3supports. There has to be at least one family per bridge type. The data for bridge family lives in a self-named folder. Inside we have family_name.png which is a screenshot of the bridge we are CEM-modeling looks like in the book. Next, we have two folders: one for a planar model of the bridge (2d) and the other for a three-dimensional model of the bridge (3d). Their contents are the same:

• An xml grasshopper file family_name_2d/3d.ghx with internalized inputs (so that it can be opened independently of a Rhino file).
• One json file and one pdf diagram for the "proof of concept" constrained form diagram (more information in the next section).
• One pdf diagram for the "proof of concept" topology diagram (this is the topology diagram that was used to generated the "proof of concept" constrained form diagram).
• N different json files that contain the parametric variations of the topology diagram.

Note that each of json and pdf files should named following the schema convention posed later on in this README file 👇🏽.

Building parametric variations of a bridge family in grasshopper

You might be thinking to all of the above, "okay, but how do I actually model and parametrize the bridge family with compas_cem and grasshopper?".

There is not only way to do this. However, there is the gist of a workflow that we should stick to speed up the modeling process. Furthermore, the components to export json and pdf files has been automated and encapsulated into grasshopper clusters for us (check out zermattA_2d.ghx and copy paste parts 02 and parts 03 of this grasshopper script) --so that is one thing off our lists so that we can focus our attention in the main goal of this dataset-building task: to take a wireframe unlabeled model and construct valid topological diagrams that are compatible to do form-finding and constrained form-finding with the CEM framework.

Here are our conventions to keep our approach consistent:

• Rhino units are meters.
• Use the context.3dm as template as your base Rhino model to work on. All the bridge family models should cover a span that is 10 meters long (this is already defined in context.3dm). We care about the proportions of the structure, not about its dimensions (i.e. just scale the the models in Rhino so that they look as close as possible to the images in the book catalog. ).
• We apply line loads of 1.0 kN/m to the structure.

Here is one way to approach the modeling workflow in either 2d or 3d for a bridge family:

1. Download the context.3dm folder from this repo. It contains helper geometry (including what looks like a river!) to give some context to our bridge design problem. It also has the right span we are using for all the bridge models (10 meters).

2. Build a proof-of-concept model (the simplest possible working version of the topological, form and constrained form diagrams):

   • Sketch a wireframe line model of the simplest possible version of the bridge on paper and think about what parts of the structural system will be in tension and which will be in compression.
   • Sketch a wireframe line model of the proof-of-concept bridge on Rhino. This model should contain the least amount of edges possible to represent the bridge structural system. Bear in mind we need line segments to be fed into compas_cem (just as with any other FEM design tool, like Karamba). You can model stuff as polylines, but don't forget to explode them into individual line segments before passing them into compas_cem.
   • Check out zermattA_2d.ghx and copy paste parts 02 and parts 03 of this grasshopper script. This is boilerplate template code that takes care of visualizing topology and form diagrams, as well exporting the pdf and json files.
   • Manually select and import what line segments in Rhino will become trail or deviation edges in compas_cem. It is helpful to further distinguish them according the force state we think the structural system will have. That is, trail edges in tension and in compression, and deviation edges in tension and in compression.
   • Try and err building a topology diagram. Visualize it with the visualization template code we copied earlier. Try to use as few auxiliary trails as possible. At the end of the day, when the compas_cem components called TopologyDiagram and Build Trails are not red, we know that we have a valid and working topology diagram!
   • Once you have a valid topology diagram, form-find it with the FormFinding component. Most likely, we will get a form diagram that does not look like what we originally envisioned. But be patient. Try to tweak the input forces and lengths that parametrize deviation and trail edges, respectively, until the form output by FormFinding is somewhat close to what we imagined the form should be.
   • Run a constrained form-finding routine with the ConstrainedFormFinding component to run the extra mile and automatically get the form we imagined. Formally, we are generating a constrained form diagram in this step. Don't forget to include the minimization of forces in the auxiliary trails. Note that there will be times where the constrained form-finding will not converge because the underlying optimization problem is too big, over-constrained or under parametrized. Try increasing the number of optimization iterations, decreasing the penalty convergence threshold, increasing the bounds of the optimization parameters. At last, try changing the topology diagram.
   • At this point we have valid topology and constrained form diagrams. We export pdf and json filed from them using the export template code we copied earlier from zermattA_2d.ghx. If you are working with a 3d model, don't forget to properly fix a camera plane that is input to the Make2d operation so that the exported pdf diagrams are neat, reproducible and consistent!

3. Now that we have build and exported "proof-of-concept" topology and constrained form diagrams, we can start making parametric variations of the topology diagram of the bridge. The parametric variations are just about changing the number of subdivision of the elements at the deck level of the bridge. The convention is that we expect to linearly increase the number of subdivisions from 2 or 3 (depends on the bridge being modeled; should also be the number of subdivisions in the "proof of concept" form and topology diagrams) up to 20. We export json and pdf files of each of the topology diagrams resulting from subdivision variations.

Naming convention

To identify our data, we set a consistent naming schema. The idea is that the name of any two diagrams is unique. Therefore, any file must be stored using the following filename:

familyname_diagram_2dor3d_numnodes_numsupports_numloads_numedges_numtrailedges_numdeviationedges_numauxtrails

Here is a fictitious example:

warrentruss_T_3d_10_2_5_20_15_5_1.json

Let's break the name down: this is the JSON file of the topology diagram of a 3D structure that belong to the warrentruss bridge family. The diagram contains 10 nodes of which 2 are supports and 5 have a load applied onto. Similarly, of a total of 20 edges, 15 are trail edges and 5 are a deviation edges. This topology diagram contains 1 auxiliary trail.

The snapshot image of this topology diagram would have the exact same name, but the filename extension would be .pdf instead of json

If this was a form diagram instead, the last three attributes would be dismissed because a form does not know the distinction between trail and deviation edges.

Schema description

• familyname: The (arbitrary) name we give to a unique bridge type.
• diagram: What diagram are we looking at? Could be either T or F for a topology and a form diagram, respectively.
• numnodes: How many nodes are in the diagram?
• numsupportnodes: How many nodes have supports assigned to them?
• numloads: How many nodes have a load applied onto them?
• numedges: The number of edges in the diagram.
• numtrailedges: The number of trail edges in the diagram.
• numdeviationedges: The number of deviation edges in the diagram.
• numauxtrails: The number of auxiliary trails in the diagram.

Citation

If you use this dataset, please cite it:

@software{bridges_dataset,
    title={{The CEM Framework Bridges Dataset}: A dataset of bridge topologies, forms and forces},
    author={Pastrana, Rafael and Skepasts, Mark and Parascho, Stefana},
    year={2021},
    url={https://github.com/arpastrana/cem_dataset},
    note={https://github.com/arpastrana/cem_dataset}
    }

Disclaimer

This project has been partially funded by the Princeton Mellon Initiative for Architecture and Urbanism.