Another architectural icon in Chicago is currently under construction. The Nichols Bridgeway, designed by architect Renzo Piano, will connect the Art Institute of Chicago’s upcoming Modern Wing (also designed by Piano) to Millennium Park, adjacent to the city’s Loop area. Unlike the curving bridge designed by Frank Gehry in the northeast section of the park, Piano’s pedestrian bridge will be a straight, slim, sword-like structure. It will rise gently from grade level near the southwest corner of the Great Lawn of Gehry’s Pritzker Pavilion to cross 23 ft above Monroe Street and land at restaurants and a sculpture garden 60 ft above on the third floor of the Modern Wing.
AISC member Chicago Metal Rolled Products was consulted by the program manager, the Rise Group, in late 2005 concerning this bridge, whose cross section will look something like the hull of a ship, with curved steel plate on the bottom, a flat surface on top, and stiffeners in between. Specializing in curving structural steel, sheet, and plate, Chicago Metal’s reputation for precision forming was strengthened by having curved 570 tons of 12- to 20-in. diameter pipe for the trellis over the Great Lawn at Millennium Park.
The 600-ft-long footbridge will have five supporting locations in the park and two off of cantilevers at the Modern Wing. The design includes 3⁄8-in., ½-in., and 5⁄8-in. plate that’s 12 ft wide and 20 ft long and curved to a 10-ft radius. The top of the bridge will have a walkway that’s heated in winter to melt ice and snow.
In something of a role reversal, both the program manager and the general contractor, Turner Construction, asked Chicago Metal for referrals on structural steel fabricators whose expertise matched this challenge, and eventually chose AISC/NSBA member Industrial Steel Construction of Gary, Ind., a company known for its extensive national bridge work.
The design went through several iterations before it was decided that the bridge would incorporate a box girder with a curved bottom covered by a curved soffit plate. A mock-up of a 10-ft-long section of the bridge was constructed with both a welded and a bolted joint. Piano viewed the structure as it was hoisted to the height where it would connect to the Art Institute. After an afternoon and evening viewing (with uplighting), he approved the prototype with further refinement of the weld preparation, and construction of the bridge began. The bridge will be factory-built in 70- to 90-ft-long sections in Gary, shipped to the jobsite, and supported by falsework while the sections are bolted and welded together. The completed structure will incorporate a 2,000-ft-radius camber and a 200-ft span over Monroe Street.
The Modern Wing is scheduled for completion in 2009.