This prototype chassis for a tower unit is 10 ft high by 12 ft wide by 30 ft long, formed from welded 6 in. square thin walled tubing. The building will require 930 such units. © Kevin Preston/Banker Steel
A high-rise residential tower to be erected in Brooklyn will soon begin to take shape in Lynchburg, Virginia, as developers take modular construction to new heights.
January 22, 2013—Construction will begin soon on a large facility in Lynchburg, Virginia—a 32-story residential tower ultimately destined for the corner of Dean Street and Flatbush Avenue in Brooklyn, New York. Developers believe the structure will be the largest tower in the world to be built using modular construction when it is completed in 2014.
The Atlantic Yards B2 Modular, as it is currently called, is being developed by Skanska, headquartered in Solna, Sweden, and Forest City Ratner Companies, in Cleveland. It will be the first residential tower in the 22-acre Atlantic Yards development near the Barclays Center, a recently completed indoor arena that is home to the Brooklyn Nets basketball team. Atlantic Yards is envisioned to eventually comprise 16 high-rise buildings with a mix of residential, retail, and office space. (See “Barclays Center Delivered Using BIM,” Civil Engineering magazine, July/August 2012.)
The new tower will begin as 930 steel tube chassis fabricated and welded by Banker Steel, of Lynchburg. Banker Steel worked with Forest City Ratner on the Barclays Center, and the success of that relationship led the two companies to discuss how the modular concept could be used on this project.
“We just think it’s a fantastic idea,” says Chet McPhatter, the chief operating officer of Banker Steel. “We have built some prototypes for them. And everybody is excited about it and thinks it’s the wave of the future as far as residential construction in large cities.” And the movement isn’t just affecting residential construction; modular construction is one of several trends noted by the architecture, engineering, and construction (AEC) consulting firm FMI Group, of Raleigh, North Carolina, in its recent report on changes in the AEC profession. (See “Construction, Engineering Trends Are Worth Watching,” Civil Engineering online, January 15, 2013.)
For the Brooklyn project, the chassis are 10 ft high by 12 ft wide by 30 ft long, formed from welded 6 in. square, thin-walled tubing, McPhatter says. Smaller tubing is utilized for purlins. Corrugated steel decking 2 in. thick is then installed in the floor and ceiling of the unit. Finally, a 0.75 in. thick layer of cement board is installed as a subfloor. The chassis are then delivered to a facility at the Brooklyn Navy Yard.
“They are fitting them out with everything that you would need for a residential building,” McPhatter says. “The tile, the sheetrock, the electrical, the plumbing, the countertops. It’s nearly a completed unit as it’s going to go to the field.
“You can combine them to make bigger apartments or bigger rooms as needed,” McPhatter adds. “So when they are assembling them in the shop, they will actually put some of them side by side, or have four of them together to create an area of the building to make sure it all aligns and matches up.”
The units will then be delivered to the job site in Brooklyn, where they will be fitted into a structural steel frame that will transfer the loads. A specially designed gusset plate system that is subject of a patent application will be used to secure the units to each other and to the building’s frame.
“We have an erector on-site, and they are essentially stacking these things like Lego blocks,” McPhatter says. “It’s a 32-story building, and it’s going to weigh about 4,500 tons, which is much lighter than a typical 32-story building in New York City.”
In fact, the building will be so light that engineers are specifying dampers at the top of the structure to control movement, McPhatter says. To ensure that the units fit together within the 0.5 in. tolerances the project requires, the team is using building information modeling (BIM).
“[BIM is] definitely something needed with as tight tolerances as these things are,” McPhatter says. “You have to have extremely tight tolerances on all dimensions, but especially on the heights of the members, for the heights of the boxes’ chassis, and obviously the widths as well, just to maintain the elevations and the coordination between the two of them.”
Modular construction brings many advantages to the project. Approximately 60 percent of the construction will take place off-site in a controlled environment. Workers assembling the modular units will need to be no more than several feet off the ground compared to the multiple stories high that they would need to be if working in the field.
The identical nature of the 930 units will enable workers to make repetitive cuts on steel members, the shop in Lynchburg effectively becoming an assembly line. Banker Steel is building a new facility for the project and expects to complete the chassis in approximately six months.
“We think this is the future of construction for residential towers,” McPhatter says. “They are doing this in Europe. They are doing this in Asia. The labor that you are saving by being able to do a lot of the work in the warehouse off-site—as compared with doing it in the air on-site—is a tremendous cost savings for the owner.”