With the foundations in place, 1,125 tons of steel have been rising on the site of Paul Milstein Hall, including five trusses that support the building's massive cantilever.
Work on the steel framework began in April and will be completed by July, when contractors start pouring the concrete floor and roof for the college's new three-level home. The design of the steel framework is controlled by the cantilever, which spans 48 feet for a length of 150 feet. The cantilever was added to the project after the initial design called for columns to support the structure along University Avenue.
"Cantilevers in and of themselves are unique in buildings, and they require more structural design, larger steel members," said Ziad Shehab, an associate with the Office for Metropolitan Architecture (OMA), the Rotterdam-based firm that designed Milstein Hall.
While trusses used in buildings are often hidden behind walls, the five trusses in Milstein Hall will remain exposed in the completed building. "The way this system of trusses expresses the different forces is something the students will be able to see and experience," Shehab said.
Another unusual feature is that the trusses will be a hybrid of two types: the traditional truss design, consisting of an upper and lower beam, with diagonal beams in between forming triangles; and the Vierendeel design, including an upper and lower beam, with vertical members in between.
The trusses that directly support the cantilever have diagonal beams and are also thicker because they will carry most of the load. As they move toward adjacent Sibley Hall, the trusses will use vertical beams since that section of Milstein Hall is supported by columns.
"From a structural point of view, it's rare that you have this mix of hybrid trusses," said Alastair Elliot, an associate with Robert Silman Associates, the New York City structural engineering firm for the project.
The steel beams were fabricated by Canatal Industries of Thedford Mines, Quebec, which purchased them from a steel mill, welded them together and shipped them to Cornell one at a time.
Once at the Milstein Hall site, the steel framework is being erected by Fast Trek Steel of Coxsackie, N.Y. The contractor has employed 18 ironworkers from the Ironworkers Union, Local 60, which covers an area extending from Rochester to Binghamton. Three additional workers from Clark Crane and Rigging of Syracuse have been on site placing the beams onto the structure.
Using a 600-ton crane, the workers lifted the beams, each weighing 62 tons, which are the heaviest pieces of steel that have been set on a Cornell building, said George Colvin, president of Fast Trek Steel.
Workers from Fast Trek are assembling the steel beams on the site and welding the trusses together. All the welds are then ultrasonically tested for quality. "They bounce sound waves through the steel looking for any cracks or imperfections in the weld," Colvin explained. "If anything is found, we reset the imperfection. But so far we haven't found anything."
The process for installing the trusses also requires they be held three inches above the height where they will eventually settle after the concrete floors and ceilings are added, said Jason Edsall, project manager for Welliver McGuire of Montour Falls, the construction manager for Milstein Hall. The cantilever is supported by 17 shoring towers, which will hold the structure in place until the welding is completed.
Sherrie Negrea is a freelance writer for the College of Architecture, Art and Planning.