The developer Bruce C. Ratner unveiled the design Thursday for what would be the world’s tallest prefabricated steel structure, a 32-story residential building in Brooklyn at the corner of Flatbush Avenue and Dean Street in the $4.9 billion Atlantic Yards project.  The 350-unit building would use varying rectangular shapes, colors and glass to break up the mass of the structure, which would sit snugly up against the Barclays Center, the arena for the Nets that is to open in September. Mr. Ratner, chief executive of Forest City Ratner, said that prefabrication, or modular construction, could save construction time and cut costs by as much as 25 percent. Fourteen other residential buildings would be built at Atlantic Yards using the approach. The second tower would be even taller, 50 stories.  Forest City Ratner is also negotiating a labor agreement with construction unions, which have supported Atlantic Yards but could end up with fewer jobs and lower wages for some trades if modular construction is used.  Mr. Ratner said Thursday that he hoped to begin construction early in 2012. But the start date has been a moving target for more than a year. He may ultimately decide to build the first tower conventionally. But Mr. Ratner’s company has now invested two years in studying modular construction, a technology that has existed for decades but is untested at this height. The world’s tallest modular building is a 25-story dormitory in Wolverhampton, England, that was built in 2010 in less than 12 months.  In New York City, the School Construction Authority has used the technology to build classrooms, and the Capsys Corporation, a modular builder based at the Brooklyn Navy Yard, has built prefabricated steel-frame housing up to seven stories tall in Brooklyn and on Long Island.  Mr. Ratner said 60 percent of the construction would take place in a factory, where an estimated 190 workers would assemble roughly 950 steel-frame modules, each 14 feet by 35 feet, and outfit them with electric and plumbing lines, as well as with kitchen and bathroom pods. At the same time, on-site workers would build the foundation. The modules would be transported to the site, lifted into place by crane and bolted together. Steel bracing would rise with the stacked modules.  The trick for developers, architects and engineers in erecting taller modular buildings has been to design an economical bracing system to protect the structure from wind shear and seismic forces. Some modular builders say the cost of a high-rise bracing system would be prohibitive. Mr. Ratner is working with SHoP Architects, the structural engineering firm Arup and XSite Modular. “If anybody can crack the code,” he said, “this group can.” The development once promised “upwards of 17,000 union construction jobs and over 8,000 permanent jobs.” The large number of jobs was a significant reason the state and the city agreed to provide $300 million in direct subsidies for Atlantic Yards.  Mr. Ratner, a union builder, said modular construction would “probably” require the same number of workers. But under current wage scales, union workers earn less in a factory than they do on-site. A carpenter, for instance, earns $85 an hour in wages and benefits at a construction site, compared with $35 in a factory setting.  Gary LaBarbera, president of the Building and Construction Trades Council of Greater New York, said, “We are in the process of attempting to reach an agreement that will work for the building trades and Forest City in an effort to create permanent employment.”  This week, seven Brooklyn workers who participated in a Forest City job-training program sued Mr. Ratner, Forest City and Brooklyn United for Innovative Local Development over unpaid wages and damages for what they said was the false promise of jobs. Forest City disputes the claims, saying it never promised union membership. As of September, it said, 19 of the 35 people who went through the program were working in related jobs. Still, the jobs issue has become a touchstone for opponents of the project like Councilwoman Letitia James, who denounced what she described as the growing distance between the promise and the reality of Atlantic Yards.
At 32 stories, the residential building would be the tallest prefabricated or modular steel structure in the world.