Buttoning up

Enclosure of San Diego Convention Center's "sails" pavilion provides an additional 90,000 square feet of space that can be leased year-round
August 11, 2010

The second-level "sails pavilion" has been a signature feature of the San Diego Convention Center since the center opened in 1989. This area, which has four sides that are each 300 feet long, is one of the largest column-free spaces in North America.

Convention center visitors have been drawn to the 90,000-sq.-ft. pavilion to gaze at its undulating, cable-supported fabric roof, to experience natural light filtering through the roof and to feel the breeze entering through its three open sides. For much of the year, San Diego's moderate climate made the pavilion a popular place. But in order to assure that it is a space that can be used year-round, convention center officials decided to enclose it.

San Diego-based contractor Douglas E. Barnhart Inc. headed the design/build team that delivered the $10 million project. Other team members included architect Joseph Wong Design Associates of San Diego; Marina del Rey, Calif.-based ASI Advanced Structures Inc., designer of the new enclosure system; and mechanical contractor TMAD Engineers.

Mic Patterson, president of ASI, explains that the enclosure project involved three types of openings: The totally open east side, the scalloped openings on the north and south sides and five oblong openings in the roof fabric that optimize the distribution of forces in its support cables. "Each of these conditions had to be treated in a manner that did not impact the fabric structure itself," he says.

A glass wall was erected on the east side of the pavilion, which was originally completely open. The wall arches gradually upward to a height of 60 feet, following the curve of the roof. It is freestanding and does not require support at the top.

The wall is cantilevered from the base of the structure using high-tensile rods.

New glazed walls on the north and south elevations follow the undulating pattern of the fabric roof, and resemble the shape of a scallop.

At the west end of the pavilion, which abuts the wall of the original convention center, a gap of about 10 feet between the wall and the edge of the fabric roof was infilled to act as a wind seal. Sealing the pavilion also involved filling in the five openings in the fabric roof that help to optimize the distribution of forces in the support cables.

Fabric "pillows" used

Originally, air-filled fabric "pillows" were to provide a connection between the top of the east wall and the flexible fabric roof. Because of air leakage problems, however, these fabric elements, which range in height from 3 feet to 10 feet, were ultimately filled with cellular polystyrene. Fabric gaskets provide a seal between the roof and the top of the north and south walls, where roof deflections are not as extensive.

The new east wall is 30 feet away from a 276,000-sq.-ft. convention center addition scheduled to open this summer. The addition was designed by Kansas City-based A/E HNTB and San Diego-based architect Tucker Sadler & Associates. Turner Construction Co. is the construction manager. With the completion of this addition and the enclosure of the pavilion, the convention center will have a total of 615,000 square feet of exhibit space.

Architect Joseph Wong says it was essential that the enclosures not detract from the nautical design concept-inspired by sailboats in the adjacent harbor. In addition to aesthetic and functional considerations, the project schedule and budget were challenging, he says. The curtain wall's unobtrusive cabling resembles masts and yardarms of ships. Seven masts, tied together with polished stainless-steel connections and high-tensile cable, support the panes.

Glass replaces fabric

At the outset of the project, fabric was expected to be the wall enclosure material. However, this option was determined to have several undesirable aspects. Because the roof fabric had aged, the color of the new fabric could not match the original. Fabric-to-fabric connections would be difficult. Most important, fabric walls would eliminate the transparency of the original wall-less pavilion, significantly altering Canadian architect Arthur Erickson's original design concept for the center. ASI proposed that the open sides be infilled with glass.

Representatives of the architect and the owner visited the Eskind Biomedical Research Library at Vanderbilt University in Nashville, which was designed by New York City-based architect Davis Brody Bond and completed in 1994. The library has an atrium with a 55-ft.-high glazed wall designed by ASI. Convention center officials returned from that trip excited by the concept of enclosing the pavilion with glass walls, according to Wong.

Wind tunnel tests on a model of the proposed design were conducted by the engineering firm of Rowan Williams Davies & Irwin in Guelph, Ontario. The enclosure is designed to withstand winds of up to 70 miles per hour, which could be spawned by the Pacific Ocean or the nearby Santa Ana Mountains.

T.J. DeGanyar, ASI's vice president of engineering, says the wind-tunnel tests focused primarily on the fact that wind loads on the fabric roof would be significantly altered because of the new wall enclosures, and also by the adjacent new addition.

Glazed walls largest expense

Using glass instead of fabric meant a nominal increase in costs, DeGanyar says. The $2.6 million cost of the glazed walls was the largest single project expense. Other major costs included $1.4 million for HVAC, $906,000 for electrical work and $323,000 for a new concrete floor.

Other enhancements to the pavilion include an HVAC system (see "Taming Mother Nature," page 42) and an electrical system. An overhead cable grid powers a new lighting system, which incorporates HID downlights at 30-ft. centers. Lighting controls allow four levels of intensity, and provide for greater illumination at the east end of the pavilion, where a stage is placed for concerts. The existing floor was upgraded to an industry standard trade show floor, with utility boxes at 30-ft. centers.

The pavilion had been equipped with large water nozzles designed to activate automatically in a fire, according to Jim Simms, project manager with fire protection and code consultant RJA Group, Chicago. A typical fire sprinkler system was not feasible when the pavilion was enclosed, so the water cannons were retained, and their control system modified.

Design/build advantages

Douglas Barnhart, CEO of Douglas E. Barnhart Inc., notes that the work was challenging, particularly because the pavilion remained in use throughout the project. It was necessary to schedule construction around 33 events. The project was completed under budget and 60 days ahead of schedule.

Both Barnhart and Wong emphasize that the extensive coordination of building team members required by the project made the use of a design/build delivery format essential.

         
 

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