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Exposition Building for the
International Celebration of Innovation

San Francisco, California, USA

Owner: Mr. John Brown
Location: San Francisco, California

This 1200 square meter, 13 meter high, building was carefully planned and prefabricated at a cost of $30,000 US and was erected in five days by one to three persons. It is an excellent example of evolutionary principles put to practice. Simple and efficient materials; Teflon coated nylon, stainless steel cables, steel re-bar and a 13 meter high steel tube, were used to great effect. Economy of materials, conservation of labor and time for construction and efficient elegance of form as function, resulted in a functional and aesthetically attractive (30,000 persons on first opening day) building which housed an exhibition space within. Particularly memorable is the experience at night when dramatic lighting produces a spectacular image--like a giant butterfly about to take flight. The building was nicknamed the "butterfly" pavilion because it seemed to bring up the image of a butterfly in most visitors' minds. The fabric structure "shell" was sewn by machine in a sail makers shop. The tension cable were pre-calculated and laid out by hand on the actual site before completion.

Construction Materials: Teflon-coated sail cloth, galvanized steel cable, forty foot high steel mast, I-beams, #4 rebar and acrylic paint.

Special Features: Donated "seconds" sail cloth material, tension-cable building membrane structure.

Owner Requirements: The building must be "eye-catching", it must enclose 5000 to 6000 square feet, it must be able to be erected within five days and the cost of the building must not exceed $30,000.00

Ecological Requirements: None

General Background of the Project: The Celebration of Innovation Exposition Committee, in San Rafael, California, was searching for an architect who could design, and arrange to construct, a building that would attract a lot of attention, be easy to erect and extremely economical to build. The secretary of the organization serendipitously went through various names in the Yellow Pages and "had a feeling" that our firm was "creative". When called, I was surprised by their "method" of choosing an architect. Further discussions presented a very challenging proposal indeed--to design and erect a 6000 square foot building within seven days of a prescribed deadline. Through in-depth talks with the Executive Director we were chosen to take on the project on the basis of some preliminary sketches which showed a giant, sail-like building constructed of anchored tension cables rising four stories to a metal sculpture centerpiece.

Since the building was to have a short-term life, it was considered a temporary exhibition building, many of the usual concerns of insulation, acoustics, HVAC systems, solar orientation, foundations, drainage, etc., could be dispensed with. Essentially the building is built like a giant spider web pulled laterally and anchored into the ground along a parabolic arch pattern. From this scallop-shaped parabolic arch rose the cables, all converging to a single point 40 feet high and expanding outward again to form an arc created by a series of points. #4 rebar was driven into the ground for anchoring. This proved to be simple and effective. Turnbuckles and rings were placed around each rebar shaft. When all points of intersection with the ground was complete, then the whole cable system was tensioned for equilibrium. It was like fine tuning a huge musical instrument.

From this tension cable web skeleton a waterproof membrane was then attached. This membrane was hand sewn from four-foot wide rolls at Pineapple Sails Company in Oakland, California. Figure 3.51G shows the sewing of the membrane which permeated the 5000 square foot workroom of the company. At the scalloped edge areas a triple layer was sewn to reinforce all edges from possible tearing under unpredictable wind loads. The shimmering quality of the material under sunlight gave it an ethereal character. The entire membrane took two weeks to sew.

The inclined steel cable in-tension created a lightweight, stable "frame" on which the sailcloth membrane roof could be attached like a translucent skin. The membrane was attached by a series of ring clips, Figure 3.51R, which connected to the taunt steel cables at strategic positions. Wind uplift was an issue to be reckoned with during construction. The membrane was unrolled from the ground upwards and clipped to the inclined cables along the way. A crane lifted and pulled the cloth into position bit-by-bit until the whole membrane sheath reached a state of equilibrium.

Figures 3.51H to 3.51Q show the erection sequence of the tent membrane structure. When the completed structure was in-place then a group of painters were to paint the finishing design onto the membrane while it was laid flat on the ground. At the time of construction there was over 30,000 feet of open parking area with which to coordinate the entire erection process.

The building has since been dismantled and the site sold to the developers of San Francisco's Design Galleria Company. The Design Galleria now stands where the Celebration of Innovation Exposition building once stood in 1987.

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