This prefabricated timber pavilion was designed by Studio Gang Architects as part of a larger redevelopment of the pond at the Lincoln Park Zoo in Chicago. The repeated curves and ultimate form of the milled glulam timber members were begging to be re-imagined as a parametric model in Rhino + Grasshopper. The modeling was taken further to a finite element model for finite element analysis.
The geometry of the structure was first ‘hard’ modeled in Rhino to explore and interrogate the form before creating a parametric model in Grasshopper. The structure consists of repeated 180 degree arcs along a common axis. The nodes of the arcs are connected with NURBS curves that are at tangents where they meet the repeated arcs. These NURBS curves are the actual timber elements in the final structure.
Left: The NURBS curve showing the 4 control points. Right: The path of the NURBS curve in relation to the repeated half-arcs.
Next, and drawing from discoveries made in the ‘hard’ model, the parametric model was defined in Grasshopper. All parameters that define the geometry can be varied:
- arc radius
- number of NURBS curves around the arc
- spacing of the half-arcs
- number of half-arc along the longitudinal axis
Left: Side elevation of the parametric structure. Right: Top (plan) view of the parametric structure.
To take the structure a step further and analyse it in a finite element software, the NURBS curves needed to be ‘split’ into single, straight elements. Finite elements cannot be curves, they must be discretized into straight, bar-like elements. An additional Grasshopper definition was added to ‘split’ the NURBS curves into elements and then define each finite element using Salamander, a plug-in for Grasshopper.
The structure was pinned at all support points and analysed for deflection at the serviceability limit state under self-weight. All members were modeled as timber elements 50mm wide x 300mm deep.
