Page B3.2 . 14 March 2007                     
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    Strutting Space

    continued

    The Trusset's unique structural detail and the custom software make small space-trusses relatively easy to manufacture, even for complex shapes. The parts are cut using a simple CNC 2D abrasive water-jet and assembled on site with unskilled labor and a minimum of equipment. The connectors are manufactured from standard sheet metal, which can be shipped flat to the site making transport relatively efficient.

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    From Idea to Enclosure

    To begin, the students develop a geometric form with the custom Trusset software running within the 3D modeler Maya. The complex curves of their design are then converted into a web of nodes and straight lines and output as fabrication drawings.

    The software also automatically generates g-code for CNC fabrication. These files drive the water-jet machinery, which fabricates the node components. The software catalogs the parts for ease in assembly.

    Each node is a composite of eight unique pieces, cut from sheets of stainless steel. After cutting, the nodes are folded and assembled by hand and kept organized in a matrix that keys them to their location within the final truss. Each strut is manually cut to a length calculated by a spreadsheet generated from the computer model.

    The assembly process moves rapidly, as the students link the nodes with matching spanning members, which are coded to indicate their positions within the truss grid. As they proceed with assembly, the shape of the node components and the lengths of the struts ensure that the truss will take its intended shape.

    The students at Columbia developed two such structures to be part of an exhibition celebrating the school's 125th anniversary. They needed to be able assemble the structures, partly break them down, move the sections, and then reassemble them in the installation space. For ease of disassembly and reassembly, the nodes were pressure fit rather than riveted.

    When the time came to move the space truss, the students brooke it into sections of a size and weight that could be carried by a single person through a standard doorway into the exhibition space.

    Inside the System

    The Trusset System builds on the advantages of the traditional space-truss modularity and structural efficiency and because of refinements in detailing afforded by CNC fabrication, adds advantages of lower cost, ease of assembly, and greater freedom in designing complex forms.

    The structural nodes are located at points of the highest concentration of shear and moment forces. They are composed of gusseted, folded steel plates connected with high-tensile bolts. The rods are composed of extruded aluminum profiles. This material has sufficient strength because the spans are modest, and the loads are primarily axial.

    The system has been tested with a variety of surface materials, including composite aluminum panels and Panelite, translucent honeycomb panels with a high strength-to-weight ratio.

    Computationally, the system is based on a square-on-square offset geometry, the most commonly used and tested space-truss configuration, and one that exhibits a high degree of material efficiency. The two-way space-truss structure is capable of spanning long distances with minimal material because of networked load sharing throughout the entire system.

    The software component of the Trusset system, which is capable of achieving complex form configurations, is designed as two primary modules. The first module operates at the design level, assisting the architect in creating surfaces buildable using the Trusset structural system. The second module performs the practical task of generating the parts inventory and the machine code for manufacturing the structural components.

    The potential for applying the system to real environments is compelling. The depth of the space-truss makes room for natural insulation and infrastructure raceways. A structural configuration can create multiple scales of open space to be enclosed within a single envelope.

    The final installation at Columbia University functioning as both furniture and wall partition featured two pieces designed to show the system's ability to deal with complex surfaces and torque. The students reassembled their structures in the school's historic Lowe Library, a classical backdrop in stark contrast with the high-tech trusses.   >>>

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    The Trusset installation on display at the Graduate School of Architecture, Planning and Preservation, at Columbia University.
    Photo: Mark Bearak

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    Custom Trusset software running within Maya.
    Image: GSAPP

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    An unfolded map of the surface, showing coding of use zones.
    Image: GSAPP

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    Each node is a composite of eight unique pieces, cut on a CNC water-jet from stainless steel.
    Photo: Mark Bearak

    ArchWeek Image

    Trusset nodes, at different stages of assembly, arrayed in a matrix that keys them to their location within the truss.
    Photo: Mark Bearak

    ArchWeek Image

    Each strut is cut manually based on a spreadsheet generated from the computer model.
    Photo: Mark Bearak

    ArchWeek Image

    For ease of assembly and portability, the nodes were pressure fit rather than riveted.
    Photo: Mark Bearak

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    Prototype of a corner quad. As additional quads are constructed, the truss takes its correct shape.
    Photo: Mark Bearak

     

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