Key Arena: recycling on a grand scale

Skilling Ward Magnusson

The Seattle SuperSonics, after playing a season in the Tacoma Dome, are moving back home to a rebuilt Seattle Center Coliseum. The new KeyArena -- Key Bank is contributing $15 million over 15 years as the building's title sponsor -- may be the first successful arena makeover in the National Basketball Association.

Despite the need for new sports facilities, no one had proposed playing basketball in any of the existing 19 economically obsolete NBA/NHL arenas built during the Sixties and Seventies -- until Seattle did.

The result is a 17,000-seat arena with uncommon sight lines and amenities including 58 luxury suites that retains the intimacy of the original Coliseum. Better yet, a typically two-year permitting and impact process took eight weeks, construction only 16 months, and the construction contract was a mere $44 million.


The coliseum was at a crossroad in 1991. Due to its age and size, it could no longer serve its primary tenant, the SuperSonics, nor compete for the concert business against larger and more modern facilities.

After Sonics owner Ackerley Communications, Inc. was unable to build an arena, the mayor asked Seattle Center officials to come up with a recommendation that would provide a new sports and entertainment venue for Seattle, preserve the public investment in the Coliseum, develop a facility that would keep the SuperSonics in Seattle, and finance the facility with no tax dollars.

So, everyone looked again at the Coliseum. Because its seating bowl was freestanding, it was possible to gut it and lower the event floor.

Initial feasibility studies by NBBJ asked three questions: 1) was the building structurally adequate to meet current earthquake codes? 2) would soils sustain a mining of the interior? and 3) could the existing roof, a cable-suspended structure which had always leaked, be reused?

Answers to two of the three questions were yes. But no one would guarantee a roof rebuilt on the cable structure which moved like a clothesline in high winds. "The last thing we wanted was to spend $50 million and have the roof continue to leak," said Dennis Forsyth, an NBBJ principal.

A new roof, it was agreed, was mandatory. Since there was strong support for maintaining the shape of roof, Jon Magnusson, principal in charge for Skilling Ward Magnusson Barkshire Inc. (SWMB), structural engineers of the project, proposed a conventional steel truss roof system that took advantage of the unique geometry of the original cable net roof.

By using the existing trusses, in conjunction with four new main diagonal trusses, the designers were able to exactly match the shape of the old roof. The four new diagonal trusses have a curved profile, similar to the drape of the original cable-net roof.

Between the new diagonal trusses and the original trusses that bisect the building in each direction, the designers were able to use straight trusses to form the curved shape of the original roof.

Supporting the new diagonal trusses with a single column each (the columns are tucked behind the last row of seats) made it possible to support the heavier roof loads with the existing structure. The rigid framing system also offers the advantage of allowing a new rigging grid and catwalks in the ceiling structure. The finances of rebuilding the Coliseum made sense.

"We were finally confident we could do it," says Bruce Rooney, director of redevelopment for Seattle Center. "What was daunting was the timeframe," says Rooney. "We started thinking about this in March 1992, got underway with NBBJ in June, went to bid in April '94, and opened bids a month later."

"This was a job that, in heaven, you would have a couple of years to do," says Jack Donovan, construction manager, PCL Construction Services, Inc., Bellevue, the project's general contractor. PCL was on site June 16, 1994, looking at 16 months to complete the project.

The first order of business was to remove the four-acre, cable-net roof. The question was where to start. Since the cable structure imposed huge loads onto the concrete edge beam, additional reinforcement had to be added to the edge beam to replace the cable loads being removed.

Cracking of the concrete was a real concern. As the cable-net roof was removed, new steel prestressing strands were added to the interior of the box-like concrete edge beam. As it turned out, the contractor was able to remove the existing cable net roof over a weekend.

Rigorous surveying of the edge beam and close observation of existing cracks in the concrete showed little deflection and no additional cracking as a result of the operation.

Left standing were the 30-foot wide edge beams and their supporting columns, the glass curtain wall, braced to the ring beam which, as the excavation progressed, would hang like a sheet of paper from clothes pins, and the triangular, 12-foot deep steel main trusses that divided the 400-foot square Coliseum into four quadrants, sitting on buttresses at the midpoints of each wall.

Rebuilding the interior seating bowl was a major project in itself. The old seating bowl was built on top of the exhibition floor, in 1965, following the 1962 World Fair. Access to seating was through two levels of concourses, the lower concourse being on grade.

Because of the low overhead at the roof outer edges, the bowl profile was relatively flat. The 1995 renovation included the complete removal of the existing seating bowl, excavation of the exhibition floor to a depth 35 feet below the level of the original floor, and the construction of an entirely new seating bowl served by five levels of concourses.

By lowering the floor 35 feet, sight lines for basketball are vastly improved, since all 17,000 seats are located as close to the playing surface as the bowl geometry permits, while retaining the intimacy of the original building.

The increased depth allowed the designers an opportunity to provide a complete level of luxury suites, a must in modern facilities. By accessing the seating bowl from five levels, instead of the original two, convenient access to concourse concessions and rest rooms are markedly improved.

"A tight construction schedule drove the decision to utilize as many precast elements as possible in the structural system," says Brian McIntyre, project manager for SWMB. "The precast portions of the structure were being fabricated while the site was being excavated. Precast also took advantage of the great amount of symmetry found in the building."

The 30 raker bents, with their spread footing and drilled pier foundations, are cast-in-place concrete. All elevated slabs are built from 12-inch thick precast hollow-core planks with three inches of concrete topping. The interior bowl surface is constructed from precast riser sections that are bolted in place.

Demolition and excavation were the leading edge of the critical path. "When we came upon the footings supporting the structure, we struggled," said Donovan. "As we went deeper, the bowl tightened. Space shrunk. We had a lot of people in the same spot at the same time. Safety became a concern and we couldn't get the cranes in until we excavated to the bottom of the bowl. I felt like the guy choreographing a halftime show at the Super Bowl."

Another aspect of the new facility that makes it a winner for Seattle Center is the ability to quickly change the floor and seating configuration from a basketball arena, to a concert hall or to a hockey facility, in a minimum of time.

The exhibition floor is served by a truck ramp and staging area. Seats that must be removed from the basketball configuration for concerts or hockey are retractable. Overhead sound and lighting systems for concerts can be rigged from a fixed, 108-foot by 72-foot fixed grid. With the ability to quickly reconfigure the facility, the new Key Arena can host different type events on consecutive evenings, and even on the same day.

According to Rooney, "It used to take us forever to make the changes necessary to convert the facility for a concert or a hockey game. With the new facility, we can host a Sonics game at noon on Saturdays and a hockey game the same night."

Recycling was an integral part of the project. All of the wood, steel and concrete from the demolition was either reused in the project or sold to recyclers. The original acoustical panels, the panels attached to the roof that keep the space from echoing, were refurbished and reused. Over 200,000 cubic yards of excavated fill was relocated to the Interbay site, where it will be graded and used for a golf course.

With development costs, architectural and project management fees and 17 separate owner's contracts, Key Arena's total cost is nearly $74 million. "We like to think we got $133 million worth of project for that price," said Rooney, "due to the reuse of the Coliseum's shell, land value and the public-private partnership between Seattle Center and Ackerley Communications, Inc., and other financial resources."

"This is the kind of project most people wouldn't even consider because it looks so monumental," Forsyth said. "As it turns out, recycling buildings can be very good business."

Project details

Howard Burton is a structural engineer with Skilling Ward Magnusson Barkshire.

Return to Design 95 top page