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The Gourd, San Antonio, Texas

The Gourd, San Antonio, Texas

By American Institute of Steel Construction | May 5, 2016

Photo: Patrick Winn

Owner*: Overland Partners, San Antonio

Architect*: Overland Partners, San Antonio

Structural Engineer: Datum Engineers, San Antonio

General Contractor: Overland Workshop, San Antonio

*Firm that entered the project in the IDEAS2 contest

Built for the San Antonio Botanical Gardens’ human-sized birdhouse competition, The Gourd is a testament to working for and with community, and offers a playful platform in which to contemplate the complex relationship between humans and the natural world through expressed structure.

Rather than pursuing a form that resembles a small human house—as is typically seen in most manmade birdhouses—the design team chose a form inspired by the bottle gourd, first used in its hollowed-out form by Native Americans to attract Purple Martins as a nesting spot. The organic form inspires creativity and imagination—particularly in its youngest of users who have affectionately nicknamed the structure their “pineapple house” and “spaceship”—while pushing the limits of digital design and fabrication.

The Gourd is built out of 70 plates of 12GA Cor-Ten steel that are wrapped around a robin’s egg blue internal octahedron structure, and perforated with over 1,000 Ball Mason jars. The jars illuminate the interior space while providing a visible connection to the outside world. Each steel plate, unique in shape and size, was fabricated using CNC laser cutting technology and emulates the pattern of a dragonfly wing.

This steel structure is comprised of three main components: the schedule 80 steel pipe legs, the rolled pipe octahedron frame, and the Cor-Ten steel skin.

Fastening at only three points around the base of The Gourd, the schedule 80 steel pipe legs provide the structural connection to the ground, with three concrete spread footings providing the foundation for the legs to rest on. These three spread footings are connected together via underground tension cables and turnbuckles to prevent each footing from splaying in the direction of the angled leg.  

The steel octahedron structure is fabricated from rolled arcs of schedule 40 pipe and is fastened at their intersections with custom laser cut and bent steel hubs. The hub detail is a pivotal part of the design as it mediates the connection between the rolled pipe frame, the three schedule 80 steel pipe legs, the tube steel floor, and the steel skin. Each hub is designed around an X-shaped disk with four rounded arms, laser cut out of ½-in. plate steel, and then bent inward 15-degrees with a CNC-brake. On the upper end of The Gourd, these disks have a 3-in. extension pipe connecting a round bolt plate for fastening the steel skin. At the lower three connection hubs, the extension pipe is fastened on both sides of the "X" disk and is gusseted with ½-in. plate for additional transfer of lateral loads to the legs. The extension on the exterior of the octahedron connects the frame to the legs, sandwiching the skin plates between two round bolt plates. On the interior of the octahedron, the extension pipe connects to a 1-½-in. threaded stud that provides a bolted connection to the three bent steel "J" plates that float the floor off of the structure.

Bent by hand through the process of assembling each faceted plate together, the steel skin becomes a tensile balloon once fully assembled and can be self-supporting. As each plate flexes inward, the skin self inflates while also providing the tensile support to lift the neck of the bottle gourd into its cantilevered position. Combining the structural support of the skin with the structure of the octahedron, The Gourd can delicately rest on the slope of the site while supporting live loads from occupants as well as additional dead loads from the integrated exterior glass apertures.

Fabricated and assembled in house by the design team, the project provided young designers a firsthand education in material characteristics and craftsmanship, as well as working as part of a production team. The project serves as an exemplar model of high-end digital fabrication and finely honed craft, bringing an experientially unexpected space to life for the local community.

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