Part 1 — Design Pitch
Intended Users
Early-stage structural engineers and AEC professionals who need a quick way to evaluate truss bridge options without running full models or doing lengthy hand calculations.
The Need
Choosing a bridge typology early in design usually comes down to experience or slow manual work. TREAT gives designers a faster way to input basic parameters, set performance limits, and see which truss configuration gets the job done with the least material.
Inputs
- Bridge span
- Number of panels
- Uniform load
- Max allowable displacement
- Max allowable axial force
- Bridge type selection (Warren or Pratt)
Underlying Logic
Truss geometry is generated parametrically in Grasshopper, fed into Karamba3D for structural analysis, and optimized using Galapagos. A penalty function keeps Galapagos from accepting configurations that exceed the displacement or force limits.
Outputs
- Optimized minimum total member length
- Maximum displacement
- Min and max axial forces
- Color-coded deformation and force diagram in Rhino
Proposed Scope
The minimum viable product is two truss typologies with parametric geometry, Karamba3D analysis, and Galapagos height optimization. Nice to have features would include arch and cantilever types, a side-by-side comparison output, cost estimation, and an efficiency ranking across typologies.
Part 2 — Implementation
What Was Built
TREAT runs in Grasshopper with the Karamba3D plugin. The tool generates truss geometry using native Grasshopper components, analyzes it through Karamba3D, and uses Galapagos to find the minimum total member length by varying bridge height until both performance limits are met.
What Changed Along the Way
The original idea was to compare four bridge typologies — Warren, Pratt, tied arch, and cantilever. The free version of Karamba3D caps models at 20 structural members, which forced some changes:
- The tied arch and cantilever were both modeled but had to be cut — they exceeded the member limit and couldn't be analyzed
- The Pratt truss was scaled back from 6 panels to 4 to stay within the limit
- The Warren truss works within the same constraint
The final tool ended up as a two-typology comparator rather than the original four-way study, but the core workflow and optimization logic are fully intact.
How to Use
- Set span, panel count, and load with the input sliders
- Select bridge type using the Value List toggle
- Set displacement and force limit sliders
- Run Galapagos to find the optimal height
- Read results from the output panels
What Couldn't Be Achieved
A full typology comparison including arch and cantilever bridges wasn't possible under the free Karamba3D license. With a full license the tool could be expanded to its original scope pretty easily since the geometry for both types was already built out.
