World Trade Center Transportation Hub (The Oculus), NewYork City. Photo: COWI North America
11,500 tons of large steelwork pieces. A sequential erection, rather than shoring, allowed the geometry and load paths to be measured through- out construction. Essential to the segmental erection process was the staged construction computer analysis model created for the project. Erection tolerances for the structural steel were exceedingly tight. In order to allow the glazing to fit properly, the steel in the arch and the columns had to be within 1/2 inch of the theoretical design location. The project team used the model to determine the cambered shape of each individual steel segment, the stresses in the structure, and the po- sition of the geometry control points during each stage of the erection. Design architect and structural engineer is Santiago Calatrava. Manag- ing engineer, engineer of record, managing architect, and architect of record are the Downtown Design Partnership, an STV/AECOM joint venture, in association with Parsons Transportation Group. Merit Award: 111 Main, Salt Lake City — 111 Main suspends the en- tire perimeter of a 387-foot-tall, 24-story tower above an adjacent five- story theater. An air rights agreement allows the tower to extend above the theater starting at Level 5. Located in a region of high seismicity, a balanced two-way, 3D steel hat truss system at the penthouse roof level balances load and supports 18 perimeter columns and long-span steel floor framing. Six articulated structural steel bearings (typically located at a building’s base for seismic isolation) support the steel hat truss system and direct the compressive gravity and lateral forces from
the hat truss to the tower’s high-strength concrete core walls, and ac- commodate temperature changes of the exposed hat truss. The hanging perimeter steel columns create open office lease spaces free of interior columns as well as a completely column-free lobby with no perimeter columns meeting the ground level. Measuring 28 feet, 1-1/2 inches deep and weighing 1,870 tons, the structural steel hat truss system extends 40 to 45 feet from the core walls. The building is tuned with longer clear spans for the 20 suspended south-side levels to balance the load of the shorter spans in the 23 suspended north-side levels. The central reinforced concrete core walls provide the tower’s only con- nection to its complex foundation and resist all gravity loads, as well as wind and seismic vertical and lateral loads. Structural engineers are Skidmore, Owings & Merrill LLP, San Francisco, and Dunn Associ- ates, Inc., Salt Lake City. Merit Award: U.S. Bank Stadium, Minneapolis — Structural engineer Thornton Tomasetti teamed with Dallas-based architect HKS to make the $825 million, 66,200-seat, Minnesota Sports Facility Authority’s vision of a climate-controlled, amenity-rich, multi-purpose venue a reality. Comprising more than 240,000 square feet, with some panels measuring more than 420 feet in length, the three-layer Texlon ETFE (ethylene-tetra-fluoro-ethylene) polymer film, air-pressure-stabilized pillow system covering the south-sloping roof of U.S. Bank Stadium is the largest transparent ETFE roof in North America. The stadium
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csengineermag.com
june 2018
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