Surface Node
Partner: Claire Moriarty
Location: Weitzman School of Design UPenn - Philadelphia, PA
Seminar: Material Agencies for Structural Geometry directed by Dr. Masoud Akbazradeh
When: Fall 2020
The goal of the seminar was to develop novel geometric methods of structural design based on 2D and 3D graphical statics. Bespoke computational methods were developed in python through critical research and algorithmic thinking. The result is a computational tool that can be used by a designer to produce a surface-based wooden shell when given a double shell funicular form.
Design Intent
Our project emerged from considering how a node can be developed with laminated veneer lumber, overlaps, and folding. Lightness, thinness, and minimal material use were all considerations. Although the seminar was meant to develop both algorithmically and physically, the class inevitably had to be held exclusively online. Consequently, the project emerged solely as a digital experiment. The next steps are to test the bending and shear relationship our project suggests and fold this logic back into the code.
The project relies on a double shell funicular structure as the input. From there, the computational process isolates a single cell shared between two nodes to build its algorithmic complexity.
Algorithmically, we start by choosing an offset distance to create the initial thickness of the folded ribbon (a). Then, a plane is developed which intersects both the original edges, E1,1 through E2,2, and establishes what we refer to as a chimney offset, a design parameter for the final structure. In fig (d), the associated points are connected, creating four distinct polylines, which group into two pairs forming the outlines for two crossing surfaces.
The polylines are then filleted using a single radius, (R) in fig (e). In direct relation to the applied load on each funicular form member, an offset in plane with the shared edge of the linked top and bottom edges (E1,1 and E2,1 in this case) is established. This offset, (O2,1 in the call-out) will add structural depth to the edges. Because these offsets occur on the shared plane of two edges, it establishes that all node pairs will properly align with each other.
In fig (f) the surface offset is applied to the two resulting bent surfaces and is a parameter that is controlled based on the material thickness required.
Assembly Procedure
The very nature of the filleted design permits that the fabrication process can be entirely machined in an unrolled state with a 3-axis cnc machine. Taking a single unrolled surface, the pieces can be individually bent into shape. Depending on what the scale permits, the surfaces can either be laser cut veneer for a thinner structure or milled veneer-ply bent through either a steaming or kerfing process.
After two bends to a single surface, the unit is ready to be attached to its coupling surface. Hardwood pegs are used here as they will assist in the transfer of shear across the surface construction.
After a final node assembly is made, two can be connected. The algorithmic process develops mating pairs of edge surfaces so that two nodes can perfectly scissor together. As they do so, hardwood pegs can again be inserted along the lengths of the edge faces. These hardwood pegs not only connect the two faces but also translates the shear forces between connecting nodes. This is critical in a surface-based design of node shell construction as the stress will be primarily transferred through shear.
Renders
