Soldier Field, Chicago

Squeezing a modern stadium within the confines of an existing historic structure was a key issue in the redevelopment of Soldier Field.

A cross section had to be developed that was about 80 ft. narrower than a typical National Football League arena. An asymmetrical solution was developed with suites stacked on one side and cantilevered seating bowls. This created seating believed to be the closest to the field among all NFL arenas.

The long spans and cantilevers used throughout accommodate the existing structure's width and height restrictions and ensure unobstructed views.

The grandstand cantilevers extend 50 ft. from the last brace point. The south scoreboard cantilevers 90 ft. over the seating deck, and the north scoreboard cantilevers 120 ft. over the deck.

To maximize patron comfort from vibrations, tuned mass dampers were added. These monitored air shock, and spring-controlled damping systems counteract structural and rhythmic deflections and vibrations.

Because of the stadium's architectural and structural constraints, the mechanical system routing required every duct to be coordinated with beam penetrations. In all, Soldier Field has thousands of penetrations.

The beam penetrations raise issues in themselves. Each was studied to ensure the stadium's structural integrity. The mechanical systems were then coordinated to conform to the size requirements for each penetration in the steel. All other mechanical, electrical and plumbing work was coordinated to accommodate the tight interstitial space.

Game Plan for Schedule

A directive to the construction team was for the Chicago Bears football team, the stadium's main lessee, to play only one season away from Soldier Field.

The construction schedule was shortened from the typical 26 to 28 months to only 20 months. The existing stadium within the colonnades would also need to be demolished during this time.

Construction kicked off four hours after the Bears' playoff loss to the Philadelphia Eagles on Jan. 20, 2002, with a schedule that tracked the move-out process in 15-minute increments. Demolition was executed on a 24-hour, seven-day-a-week timetable.

Nine months of site preparation preceded this period. Activities that included power feed relocation, drainage, demolition of a six-story office building and asbestos abatement occurred during the time the existing stadium and adjacent museum campus were operational.

By designing a structural steel frame that mounted directly to the pile caps, the erection of the stadium frame was expedited. Due to the lack of sufficient space in the bowl for cranes, coordination of the erection of the precast concrete stadium risers and the structural steel was done by erecting the steel during the day and the precast at night.

Sitework and Schedule

The site is a landfill containing debris from the Great Chicago Fire of 1871. Instead of being removed, the fill was used to create berms and a sledding hill.

Asbestos abatement was performed on the known conditions in the existing stadium crawlspace. During the start of demolition, a significant amount of asbestos was also discovered in the soil under the stadium.

The abatement of the newly discovered asbestos could not affect the schedule. Mass demolition and abatement of the hazardous soil below the stadium were performed simultaneously while maintaining the 20-month schedule.

The surface of the bowl area was not a suitable one for construction due in part to the debris from the Chicago Fire, the need for asbestos abatement and the location of the water table less than 3 ft. below. A working surface for multiple cranes was created by using concrete rubble from the demolition.

The new stadium is founded on driven steel H-piles. Because the existing historic structure constrained the project on three sides, performing the foundation work inside the existing structure required close coordination between the excavation, pile and concrete subcontractors.

The process included close monitoring of the pile driving operation with the use of vibration sensors and the installation of drilled micro-piles where the piles were close to the existing structure.

Moving Down Field

The project team was required to maintain 2,500 parking spaces of the original surface parking area for visitors and guests of the remaining museum campus, including the McCormick Place Convention Center, John G. Shedd Aquarium, Adler Planetarium and Field Museum of Natural History.

The Soldier Field project had only one ramp for material access, and that was installed late in the process. The process before the ramp was to make use of an existing oversize gate on the south and use cranes and two material hoists to move material into the suite levels and upper concourses.

About $100 million of infrastructure work was performed concurrently with the $400 million on the stadium and integral 2,500-car, four-level underground North Parking Garage.

The jury said, "Regardless of how you feel about the design of the outside of this stadium, when you go inside, there's not a bad seat in the house. What they have done in 20 months is amazing. It couldn't have been done without teamwork.
Permitting was an achievement. They had someone living at City Hall.

"On the design side, they cut out time by designing in three dimensions and skipping shop drawings. All contractors had to literally jump in and write their own requests for information and then answer them. The geometry is too difficult to comprehend.

"Even though the design is an atrocity, the fact that they are playing in the stadium is amazing. Everyone had to work together to make that happen."

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