The operable doors provided another opportunity for VDC simulation. Each hydraulically driven door will pivot on a single jamb, a system chosen instead of sliding doors to save space, notes Aniol. On the glass-dominated west end of the stadium, five doors up to 95-ft high and 55-ft wide will pivot and open to a public plaza. Even with the higher strength steel, the ridge truss employs some massive members - the largest a W36-x-853 beam with a 4.5-in-thick flange. Grade 65 steel from ArcelorMittal, Luxembourg, was used to reduce truss weights by over 25% when compared to conventional Grade 50 steel, according to Aniol. The roof structure also includes 12 queen’s post trusses - six on either side of the ridge - spanning from the ridge beam to the concrete ring beam atop the stadium’s exterior. While the ETFE will cover roughly half the field, the angle of the roof will allow sunlight over the entire field. The north side is covered with a traditional steel deck and membrane.
That southerly exterior is covered with transparent ethylene tetrafluoroethylene (ETFE) panels, which were also used on the Allianz Arena in Munich and Forsyth Barr Stadium in Dunedin, New Zealand. The adopted design employs a 14-degree slope on the north side of the ridge and a 17-degree slope on the south side. “There was a sweet spot to lofting the roof,” says Aniol. Steeper slopes can reduce snow loads, but at some point, they become impractical. To visualize the enormous task, the TT design team used Rhino from Seattle-based McNeel North America, and Grasshopper, a Rhino plug-in, to perform parametric modeling of the structural framework and optimize the roof slope. With over half the roof transparent, “dealing with snow loads has been a challenge,” concedes John Aniol, structural engineer of record for Thornton Tomasetti in Dallas. “It looks like an iceberg and… (its) roof is steeply sloped away from the ridge to move snow off the roof,” he adds. After it leaves the roof, gutters up to 50-ft wide and 50-ft deep carry the snowmelt to a storm sewer system. “We wanted to react to the snow,” says Taylor. The design was also heavily influenced by Minnesota winters. Winter is Coming: The transparent, nautical design evokes both an iceberg and an ark. Crews refer to this beam as the “prow,” a marine term for the forward-most part of a ship bow that cuts through water. Bank Stadium’s design features a ship-like profile, with a 1,000-ft-long ridge beam running along the middle of the roof, pointing upward toward the Minneapolis skyline. HKS also designed Lucas Oil Stadium in Indianapolis, and Mosaic Stadium in Regina, Saskatchewan. Mortenson and their subcontractors would split out the pieces and give us feedback,” says architect Kevin Taylor, HKS project manager, who also helped design the Dallas Cowboys’ AT&T Stadium. “On a weekly basis, we would upload our model. Dallas-based architect HKS shared early Revit models with Mortenson for cost estimating and constructability reviews. Prior to breaking ground, Mortenson and the design team also leaned heavily on technology.
The team of six VDC personnel uses a variety of software tools, including Autodesk Revit for viewing models, Autodesk Navisworks to combine design and construction information for simulations, Synchro Software’s Synchro Pro to integrate scheduling and 3D models for 4D simulations, and various other tools as needed. “We have 30 months to build something this large,” says Ricardo Khan, Mortenson’s director of integrated construction. “To coordinate all those people, we use the best resources we can to reduce waste.” With up to 1,000 workers on-site at one time, the stadium’s general contractor, Minneapolis-based Mortenson Construction, says VDC has been the key to keeping the project on schedule. Its angular combinations of steel, concrete, glass, and other materials, along with an aggressive schedule and a tight site, have led designers and builders to rely heavily on virtual design and construction (VDC) to keep the project on track for completion. With a largely transparent roof, glass-laden walls, and 95-ft-high glass doors that open to downtown Minneapolis, the Vikings’ new home is designed to connect occupants inside with the elements outside.
Bank Stadium opens in 2016, the professional football team and its hardy fans hope the $1-billion facility will capture the best of both worlds: an indoor stadium with an outdoor feel. When the Minnesota Vikings’ shimmering new U.S.