[NYguy]

https://www.enr.com/articles/60490-team-delivers-supertall-tower-on-a-quarter-acre-parcel

Team Delivers Supertall Tower on a Quarter-Acre Parcel
The 450,000-sq-ft mixed-use tower known as 520 Fifth Avenue is being constructed on a compact site at Fifth Avenue and 43rd Street.





By Jim Parsons
March 24, 2025

Supertall buildings may no longer be a novelty, but that doesn’t mean they’ve become easier to build. Manhattan tower 520 Fifth Avenue, a 1,002-ft-tall, 450,000-sq-ft mixed-used structure on track for completion later this year is a case in point. Rising from a constrained quarter-acre corner site at the busy intersection of Fifth Avenue and 43rd Street in midtown, the project has a crowded setting that required general contractor Suffolk Construction to combine its supertall building experience with what the company says are “advanced data analytics and cutting-edge technology” to efficiently plan and execute each phase, an effort that began well before construction got underway in January 2022.

Tom Giordano, Suffolk general manager for the New York region, says that with so little room to work with, every aspect from logistics to protecting workers and managing street traffic has been addressed well in advance and synced with scheduled construction tasks to keep the project safe and on schedule. “We’ve been compiling data from the start, giving us a clear data lake to work with,” Giordano says. “We’re constantly receiving updates on progress and upcoming areas that we’ll be focused on. That helps alert us to potential problems that we can avoid.”

With an aspect ratio of 1:15, the thin profile of 520 Fifth Avenue belies a structural brawniness that begins with the site’s underlying Manhattan schist, “some of the hardest foundation material in the world,” says James von Klemperer, president and design principal for architect Kohn Pedersen Fox. “It’s a strongly resistant subsurface condition well suited for a building of this type.”

With the site long vacant since demolition of a nine-story office building in 2013, Suffolk got right to work excavating the foundation to about 48 ft below street level, removing rock using a combination of line drilling and breaking. According to the contractor, the foundation mat thickness varies from 10 to 19 ft, with walls averaging 36 in. thick. The building’s elevator pits, which continue to 60 ft below grade, are founded on a 36-in.-thick reinforced concrete pit slab.

The superstructure consists of 72 floors of reinforced concrete slabs supported by concrete columns. Along with belt floors located on Levels 32 and 52, Suffolk says Grade 97 rebar combined with concrete and steel link beams further reinforce the building core while also alleviating rebar congestion and reducing shear wall thickness.

A two- and three-day pour cycle allowed placement of the concrete superstructure to finish three weeks ahead of schedule. To speed material delivery as the building gained height, Suffolk installed a main four-car hoist complex that served the first 64 levels, with a single car hoist providing access to Levels 64-72. Another secondary hoist was used for below-grade levels.

Because a series of asymmetric setbacks narrows the building as it rises, Giordano says coordination was particularly critical to top the 76-floor concrete superstructure in October 2024 with five levels of galvanized structural steel framing and grating platforms that enclose and support a 500-ton tuned mass damper, mechanical systems and building maintenance unit. A combination of prefabrication and a select overtime system allowed structural steel work to be completed in late December, seven weeks ahead of schedule, the contractor says. In total, Suffolk says the project has more than 6,000 tons of rebar, 29,000 cu yd of concrete and 1,000 tons of structural steel.

To reduce column sizes for the building’s lower 30 stories—which include ground-floor retail, lobbies, meeting areas and 25 floors of office space with 12-ft ceilings—Suffolk built a 31-story, 24-in. by 24-in.-thick composite structural steel column on the project’s prominent corner of 43rd Street and Fifth Avenue, with the plate column tied back to the concrete shear wall core at three floors. “The columns in the building find their place in the plan without obstructing views where we wanted the views to be,” von Klemperer says, adding that even with the smaller upper-level floor plates, “we can get good depths for residential parts of the building.”

Activity now is focused on completing installation of the building’s exterior, which includes distinctive arches made of glazed terra-cotta panels on the podium levels, with painted aluminum panels for the upper levels. The exterior also includes 5,500 unitized curtain wall panels. Plans call for office floors to be completed in September, Giordano says, while residential sections are to be turned over in phases during the ensuing nine months.

“The advance planning and coordination have paid off, and we’ve had a good collegial environment across the project team,” he says. Although Rabina has not disclosed a total project cost, Giordano says the team plans to deliver the finished building on budget.