Taking tradition into the future

While the trend in sports facilities is retro stadiums, parks and arenas, Denver's Invesco Field at Mile High is a departure. The new home of the NFL Broncos fulfills the desire of the football team's ownership by propelling the tradition of the team, along with the city it represents, into the future.

Rather than replicate the revered but aged 52-year-old Mile High Stadium it replaces, the horseshoe-shaped stadium uses tradition as a building block. The white bronco statue that formerly crowned Mile High now stands atop the scoreboard of the new stadium. Tradition also is reflected in the stadium's red brick base.

Above its base, however, the stadium is wrapped in a shining, curvilinear aluminum-mullion lattice and topped with a band of aluminum panels. The undulating design of the upper bowl adds a distinctive trademark to the Denver skyline. "This stadium speaks much more to the future of this city," says Timothy Cahill, vice president and director of design for lead architect HNTB of Kansas City, Mo. "The Broncos were not into making a statement towards nostalgia. The organization was more interested in making a statement about the evolution of Denver as a technical city."

The 71,125-seat stadium is unusual in many ways, ranging from its financing to its design and construction. Seventy-five percent of the stadium cost was publicly funded by extending the sales tax that funded Denver's Coors Field baseball park. Residents of a six-county area passed the extension. The Broncos agreed to pay 25 percent of the cost and be responsible for all cost overruns.

In the first wave of new football stadiums to use the design/build project delivery method, the $364 million project was headed by Turner-HNTB, a joint venture of Dallas-based general contractor Turner Corp. and HNTB Design/Build Inc. Turner assumed 80 percent of the risk of guaranteeing the price and HNTB 20 percent. Assuming this large a risk is unusual for an architectural firm and HNTB characterizes it as an indication of its commitment to the project.

The original request for proposals called for a traditional design/bid/build delivery method. However, the Broncos wanted to play the current season in the new stadium. "Based on a conventional schedule, that would not have been possible," says Charlie Thornton, project manager for the construction team of Turner Construction Co. and locally based firms Empire Construction Co. and Alvarado Construction Inc. As a solution, the Turner-HNTB team proposed that the project be delivered under a design/build format, which would give the district a guaranteed price and delivery date.

Though not a proponent of design/build for large public projects because of perceived loss of control by the owning agency, Tim Romani, executive director for the stadium owner, the Metropolitan Football Stadium District, says it made sense. "The district has a politically appointed nine-member board without the experience to manage a project like this," says Romani, who joined the district after the design/build decision had been made. "The idea was to shift the risk as much as possible."

According to Curtis Fentress, president of Denver-based Fentress Bradburn Architects Ltd., an associate architect on the project along with Denver-based Bertram A. Brutan & Associates, the design/build process made it possible to cut by nearly half the time needed to produce the facility. However, the design/build process was further complicated by the late participation of Denver's Design Review Advisory Committee (DRAC).

Like a referee of a football game reversing a call following instant replay, the DRAC demanded significant changes be made to the stadium design. Accommodating the changes to a design that was largely developed added $11 million to the cost. In the end, Fentress says the stadium benefited from the review process. Among the changes, express elevators were added from the ground floor to the upper bowl. The open concourses on the exterior of the building were enclosed in a curvilinear, bullnosed aluminum-mullion lattice.

Low-emissivity insulated glass is recessed at an angle at the club level and above entrances, where the translucent glazing is back lit.

The abstract shape of the upper bowl evokes various images to people, even to members of the design team. Cahill says its undulating form is reminiscent of the surrounding mountains. Fentress calls the undulation a saddle shape.

"The top was always seen as a very sculptural undulating piece that is a gesture towards the cityscape and the skyline," says Cahill. In addition to its engaging geometry, the upper bowl's undulation is functional in that it rises on both sides at the 50-yard line, affording more seating where most fans want to sit. The building's brick base ties into a civic plaza, part of the city's "regreening" of the nearby South Platte River.

The design team worked to incorporate the Broncos' desire to retain and enhance many of the traditions of old Mile High. The stadium's horseshoe shape, a trademark of the old stadium, opens to a view of a giant scoreboard and the Rocky Mountains. The cantilevered construction of the upper bowl keeps Denver's stadium one of the most intimate in the league. Finally, the use of steel treads and risers continues the fans' ability to create "Rocky Mountain Thunder," the loud noise caused by the stomping of feet on the treads.

Modern stadiums typically use concrete risers and treads. Because of their light weight, the use of thin, 3/16-in. steel-plate treads and risers caused concern about their ability to dampen vibration, says Dennis Wittry, project manager for Houston-based structural engineer Walter P. Moore and Associates. The firm conducted studies to ensure that the design kept vibrations in a comfortable range.

Though not part of the original design, the stadium's modern look is partially achieved by the use of steel pipe columns and adjustable pin joint connections on the upper bowl. According to Wittry, this type of connection resulted from an effort to "come up with a better looking connection that would maximize erectability."

The use of a two-way, cast-in-place, post-tensioned concrete-slab system with post-tensioned girders and joists on the five concourse levels allowed for fewer and longer-than-normal column spans and minimized slab depth.

Construction that began in August 1999 was completed 25 days ahead of schedule, according to Emil Konrath, vice president of sports construction operations for Turner Sports. The mixed-use facility opened Aug. 11 with a concert by the rock group the Eagles. According to Konrath, the design/build team returned $5 million to the stadium district. Construction was completed without any major accidents.

Except for a controversy about the sale of the naming rights of the stadium, fans have embraced the stadium, filling it to capacity. "This is as successful a project as I've been involved with," says Romani. Broncos owner and CEO Pat Bowlen has called it "the finest stadium in the country."