$100M or greater

Merit Award Seattle Seahawks Stadium Seattle

Photo courtesy Michael Dickter, Magnusson Klemencic. Juror Comment “The idea of isolating the mass of the roof structure to resist lateral transfer loads in seismic events reflects a real sense of ingenuity by the engineering team.” Photo courtesy Timothy Hursley.

he Seattle Seahawks Stadium Steel Innovations pylons and foundations. This also saved and Exhibition Center is a $430- First-Ever Seismically Isolated Sta- more than $3 million in the construction million public-private develop- dium Roof. The stadium sits on liquifi- cost. ment project. It incorporates a able soils in a high seismic zone. In the Special Hinged Columns Take Up 67,000-seat football/soccer sta- event of an earthquake, the site’s north the Slack. With the potential for the roof Tdium, a 201,800-sq.-ft exhibition hall, and to move up to 2’ atop the dampers in the end could move a foot to the north while a parking structure on a small site just the south end moves a foot to the south, pylons, “hinged columns” support the south of downtown Seattle potentially stretching or compressing the roof around the back of the bowl to ac- The new stadium is located within the roof up to 2’. Expansion/contraction due commodate this movement. space envelope of the old Kingdome, but to temperature could be 8” in the roof. New “Slipped Nickel” Approach. A offers a new experience for spectators: Special bearings known as “friction pen- “slipped nickel,” approach to the roof two signature 720’ tied structural steel dulum dampers,” allow the ground/ geometry was developed to simplify the arches support the stadium roof, and no seating bowl to move independently roof framing and connections. A uni- columns block views of the field, down- from the roof during an earthquake, iso- formly skewed stack of circular, parallel town Seattle, the water, or the mountains. lating the roof from movement and po- planes (the nickels) became the template The project was finished one month tential damage. The ends of each 720’ for roof geometry, yielding a condition ahead of schedule and on budget. Even roof arch rest on these dampers, located where all roof beams are parallel and though the stadium has large roof sec- within the roof support pylons. Each equal length, and the roof deck is flat and tions and is located in a high seismic zone damper supports 3 million lb of vertical parallel. This simplified construction, on liquifiable soils, it cost 7% less on a load. By decoupling the mass of the roof shortened the schedule, and cut costs. per-seat basis than the last 13 NFL stadi- from the rest of the building, it was pos- Advanced Shaping Exercise Opti- ums constructed. sible to reduce the design forces on the mizes Arch Curvature. A sophisticated

April 2004 • Modern Steel Construction Photo courtesy Michael Dickter, Magnusson Klemencic. Photo courtesy Corky Trewin, Puget Sound Digital.

shaping exercise helped determine the forms. Next, the dramatic steel arch was optimum funicular shape of the roof erected with 16 A-frame components. Owner arch. Funicular—or “rope-like”—refers Precision Post-Tensioning Controls Washington State Public Stadium to the concept that between any two Roof Arch Deflection. Each tri-chord Authority, Seattle points, a rope suspended will hang in a truss is post-tensioned with 4.5 million lb Paul Allen, Seahawks owner, Seattle naturally perfect shape under a given set in 130 strands. This post-tensioned ap- of loads. This translates into an opti- proach allowed the arches to lift off the Architect mized stadium roof arch representing the erection towers, and final vertical deflec- Ellerbe Becket Architects & Engi- most economically efficient shape. tions to be precisely controlled. neer, Kansas City, MO Extensive Integration of Steel Detail- Dramatic Seating Cantilever. To LMN Architects, Seattle ing into the Engineering Design Process. bring fans as close as possible to the field, The structural steel detailer was incorpo- the upper deck was cantilevered over the Engineer rated as a part of the design team, which lower deck seating. This creates the Magnusson Klemencic Associates, allowed all the structural details to be in- longest interior cantilever seating over- Seattle dustrially “tested” (using 3-D CAD tools) lap (56’) and the most intimate sightlines and included on the structural drawings. in the NFL. General Contractor This provided bidders more precise infor- Advanced Vibration Analysis. Spe- Turner Construction, Seattle mation than would normally be available. cialized wind and vibration analyses New “Erection Structure as Final were performed on specific elements of Engineering Software Structure” Technique. The dramatic the stadium to meet performance objec- SAP Non-Linear tied-arch roof comprises two separately tives. The structural steel tower for the erected elements that work compositely scoreboard—the first portrait-oriented Detailing Software as one. The lower tri-chord truss was board in an NFL stadium—was subjected Tekla Xsteel built on the ground in seven pieces and to a special vibration analysis for wind. lifted on three erection towers. It was Vibration analyses also were performed then used as a staging platform for the for the cantilevered seating deck to avoid remainder of the roof erection, eliminat- the need for any costly supplemental vi- ing the need for additional erection plat- bration-reduction technology.★

April 2004 • Modern Steel Construction