Images courtesy of Girder-Slab® Technologies, LLC

THIN FLOOR SYSTEM: TROY BOSTON

Troy Boston is a 378-unit apartment complex located in Boston’s South End at 275 Albany Street designed by ADD Inc., now with Stantec. The project team is pursuing LEED Gold certification for the dense urban development. Two residential towers at 12 and 20 stories anchor the corner of a tight site, wrapped with a podium comprised of outdoor rooftop amenities, three levels of parking, and ground-level retail space. The project team performed an analysis to compare costs and schedule for multiple structural options: a conventional steel-framed system, a cast-in-place concrete system, and a thin floor system known as the Girder-Slab® system. All three systems were competitively bid solutions. Senior Associate Principal, Jon Lannan, AIA, of ADD Inc., noted “getting this building open before the competing neighbors” was a high priority for the developers, especially in the growing Boston market. Weather related issues during construction had to be nearly eliminated to maintain the critical path. The Girder-Slab® system was ultimately chosen as it held the advantage of fast erection which led to a shorter schedule, resulting in a more economical solution. Designed to accommodate bay sizes of 25 feet by 30 feet, the thin floor system can achieve floor-to-floor heights as low as 8 feet 10 inches when using 8-inch hollow core planks. The design team of Troy Boston achieved the desired clear ceiling heights of 9 feet 2 inches by setting the floor-to-floor heights at 9 feet 10 inches.

The 330,000-square-foot project is on schedule to complete the structural framework within 10 months. The underside of the hollow core planks is exposed and the modified beams, D-beams®, are treated with spray-applied fire protection. By achieving low floor heights, material costs are reduced in addition to saving building energy usage. Flexibility of space planning was also desired to lay out the floor plans with a dense unit mix of studios, one-bedroom, and two-bedroom apartments. To create larger bays with fewer columns, the structural team at Odeh Engineers designed the beams to span longer than 25 feet with the implementation of tree columns that were integrated within partitions. The thin floor system ultimately represents a simple design that allows for low floor-to-floor heights within a fast schedule. According to Lannan, “[We] would happily use Girder-Slab® again.”