By Edward M. DePaola, PE, and Fortunato Orlando, PE
The new corporate headquarters for financial giant JPMorgan Chase, at 270 Park Avenue in Manhattan, became New York City’s largest steel building when it topped out in November 2023. Located in midtown Manhattan on a full block bounded by Park Avenue to the east, Madison Avenue to the west, and East 47th and 48th Streets to the south and north, the building encloses 2.5 million square feet spread over 60 floors and reaches a height of 1,388 feet, making it the sixth tallest in the city.
After extensive study, JPMorgan Chase chose the site despite the presence of its former headquarters on the east half of the block, a 50-story building originally constructed for Union Carbide and completed in 1960. The older building was intended for only 3,500 employees, a quarter of the number Chase might eventually house in the new building. Furthermore, the building’s close column spacing and low ceiling heights were not conducive to modern office layouts. The potential for a large footprint, central location, and connections to public transportation, among other benefits, outweighed the effort involved in demolishing the existing structure.
Now fully utilizing the entire 200-feet by 400-feet block, the new building will provide more than twice the ground-level outdoor space, including an expansive public plaza and street-level green spaces. An open and spacious two-story lobby affords views through the building from Park to Madison Avenues and makes the office tower appear to float above. Architecturally, the tower is like a row of nine books—rectangular extrusions of the longitudinal column bays—aligned on a shelf. Each book is a different height: The east- and west-most column bays terminate at intervals, creating symmetrical stepped roof setbacks. From the highest setback to the peak, the building is only 40 feet wide.
A Challenging Site
The most significant challenge to building on the site is the presence of Grand Central Terminal and the recently opened Grand Central Madison beneath all but the western quarter of the site. The terminal’s tracks run north and south and are typically paired with a platform between them—an east-west spacing of about 60 feet—leaving only the narrow gap between adjacent tracks for the foundation for the new building. Worse, the structure supporting the trainshed roof and the Union Carbide Building occupies much of that gap.
Still, the design team, led by architects Foster + Partners and structural engineers Severud Associates, rose to the challenge. Working closely with the Metropolitan Transportation Authority (MTA), which operates Metro-North Railroad and Long Island Rail Road, the team examined the space between dynamic envelopes—often no more than 48 inches wide—taking into account existing power, signal, and other utilities that could not be interrupted or relocated without prohibitive cost. Only a few lines of potential bearing were identified, and along them, only a handful of locations were found practical.
The west quarter of the site—a roughly 100 feet width along Madison Avenue—is much less obstructed than the Park Avenue side. It has more direct support on bedrock, which gave the designers greater flexibility and a convenient place to locate the building’s service core. Additional columns could have also been located here; however, the architects desired an externally symmetrical design. Therefore, column locations were chosen that mirrored the supports along Park Avenue.
The Tabletop
Collecting the gravity and lateral loads from the tower columns—spaced at 40 feet east to west and up to 66 feet north to south—and delivering them to the selected points required an extensive transfer system. The architects and engineers studied several framing alternatives before arriving at a two-story-high arrangement of steel transfer girders and sloping super-columns and braces that came to be known as the Tabletop.
Along the north and south elevations, groups of four adjacent exterior columns slope inward and toward each other to create three fan-shaped sub-structures. Longitudinally, two 25-feet-deep plate girders span the full length of the building—360 feet—to transfer the interior columns. The girders, which also carry the second and third floors, are each supported by V-shaped columns. Together, the girders and columns form two vertical planes down the center of the structure.
Supplementing the fan and V columns are six diagonal macro-braces. At the east end, members slope upward and outward from the base of the easternmost fan columns to a point midway between the east ends of the transfer girders. At the remaining fan column bases, members slope upward and inward to the top of the transfer girders.
Despite presenting an elegant and lightweight appearance, the Tabletop puts tremendous demands on its foundation. The loads at the base of each super-column are almost 100,000 kips, while the area available at each support is only about 60 square feet. Steel base plates accommodate the bearing pressure directly beneath the columns, but below ground level, construction was constrained by two levels of railroad tracks as well as the MTA’s desire to protect the trainshed roof and minimize track outages.
A New Standard for High Performance Concrete
The design team concluded that a concrete solution was needed to create a path through the existing trainshed and down to bedrock. The concrete had to be stronger than the 14,000-psi mix successfully used on Severud’s One Vanderbilt Avenue project nearby. Higher strength concrete mixes were not readily available, so the design and construction team set out to develop one. Severud, along with foundation contractor John Civetta & Sons and concrete supplier SRM Concrete, engaged in a series of trial mixes, laboratory testing, and full-scale mock-up placements.
The first step was determining the concrete mix proportions. Cylinders were cast using different combinations of cement, blast furnace slag, fly ash, and microsilica, and tested for strength. After many iterations, the team arrived at a reliable and affordable concrete mix with a 56-day compressive strength of 16,000 psi. As a bonus, the cement content is only about a third of the total cementitious material, reducing the concrete’s carbon footprint.
With the strength issue resolved, the team turned its attention to placement concerns. Given the limited accessibility and the heavy reinforcement that was needed, getting the concrete into the forms without affecting its properties was of great importance. Mock-up panels of the 48-inch-thick piers were constructed, 8 feet wide by 8 feet tall with multiple curtains of heavy reinforcement. Concrete was placed in the forms using a pump with 100 feet of hose and from a height of 40 feet to simulate how it would be placed in the field. At 3, 7, 14, 28, 56, and 90 days of curing, cores were drilled from the mock-ups and tested for strength; the results were within the same range as lab-cured cylinders.
The mock-ups were also used in a parallel study of temperature effects. Due to the high cementitious material content, hydration produced elevated temperatures. Thermocouples were installed throughout the test panels to monitor the concrete’s temperature near the surface and at depth. Methods to attenuate the effects were explored, such as embedded water pipes for cooling, but most were found impractical.
Eventually, the team determined that spraying liquid nitrogen—at minus 320°F—into the mix during batching cooled it sufficiently—typically, to a maximum of 58°F—to remain dormant (an inert element, nitrogen vaporizes and dissipates with no permanent effect on the concrete). Once placed, the concrete began to warm but monitoring revealed that during the first 72 hours of curing, the concrete temperature remained well below a calculated maximum of 186°F. Further, the differential between the surface and core temperatures never exceeded 35°F.
Although development of a 16,000 psi concrete mix presented several practical issues, careful study resolved all of them without penalizing code requirements, workability, cost, and schedule, and ultimately resulted in consistency in the final strength. In fact, by the end of the project, testing of more than 7,600 cubic yards of concrete revealed an average strength closer to 20,000 psi and a maximum strength of 23,000 psi, setting a new standard for high performance concrete.
Lateral System
The structurally elegant lateral system for 270 Park Avenue consists of five parts: the ground floor and walls below; the Tabletop; the braced tower core; five levels of outrigger trusses; and the exterior macro-braces, which are configured in a distinctive diamond shape on the east and west facades. Working together, the core, outriggers, and macro braces carry the horizontal shears and moments from the superstructure to the Tabletop. The Tabletop—which acts as a space truss with rigid top chords—transfers the loads to the ground floor.
In the north-south direction, the braced core and outriggers work in conjunction with the exterior diamond frames to provide the lateral resistance and a smooth drift curve. The outrigger trusses distribute lateral-induced vertical forces to the spandrel columns, increasing the effective width of the system. At ground level, the core and Tabletop braces deliver loads directly to the supporting concrete walls, even those located between train tracks. With few closely spaced supports, however, the uplift forces generated are extremely high—on the order of thousands of kips.
The foundation walls are supported by 13.5-inch diameter caissons, drilled into bedrock from the lowest track level. For uplift, the caissons are post-tensioned with three No. 32 (4-inch diameter), Grade 75 threaded bars. The traditional approach to anchoring the column bases—two levels above the foundation—is to install prestressing tendons from the caisson cap or the bottom of the wall and post-tension them from the ground level. The design team chose this route, but with an ingenious turn.
Post-Tensioned Solutions
Concerned that a failed dead-end anchor might not be repairable or replaceable at track level, engineers devised a system of U-shaped ducts for the tendons, with both openings at ground level, that dip to the bottom of the caisson cap to engage the rock anchors. After proving the concept with the full-scale pier mock-ups, tendons of 27 strands each were fished through the ducts, passed through holes in the massive column base plates, and tensioned with a jack at each end, working simultaneously.
In the east-west direction, spandrel beam offsets to accommodate the curtain wall on the north and south facades prevented significant utilization of moment-resisting frames. Consequently, all lateral load is collected in braced frames located on the north and south sides of the office core. Again, outrigger trusses were placed at mechanical floors along the building’s height to engage the spandrel columns and increase the effective width of the frames.
Above the 14th floor, all the elevator shafts shift eastward from Madison Avenue to the center of the floor plate in a more traditional layout. Here, the multiple-floor transfer, known as the sky lobby, creates a livable space at the center of the building with a conference center and recreational facilities. The outrigger trusses at the 11th floor redistribute lateral loads from the terminated core bracing along the length of the Tabletop plate girders.
Train tracks and platforms prevent the transfer of lateral load from ground level to foundation. As a result, the ground floor slab over the trainshed is used as a gigantic drag strut to deliver the lateral forces from the columns bearing over the trainshed to the western portion of the foundation. The 16-inch thick slab has a concrete strength of 10,000 psi and is post-tensioned with four groups of four tendons aligned with the column bases.
The tendons, each composed of 55 strands that required specialized jacks from France to be tensioned, are anchored by the cellar walls and ground floor slab at the west quarter of the site, a portion of the building that the design team refers to as “terra firma.” Due to the tremendous shear stresses, the slab is 36 inches thick, with a strength of 10,000 psi and post-tensioning in both directions.
Motion Control
The response of the building to wind loads, especially at service levels, was an important component of the structural design. Severud worked closely with wind engineering and micro-climate consultant RWDI to develop performance criteria and confirm that strength and serviceability targets were met. RWDI engineers performed detailed wind tunnel testing and multiple rounds of analysis to determine the wind-induced structural responses in each principal direction and in torsion.
Using the wind tunnel data, dynamic properties of the structure, and a statistical wind climate model for New York City, they predicted peak accelerations and torsional velocities for one-month, one-year, and 10-year recurrence interval events. Initial analysis of the lateral system response to these events revealed that accelerations at the uppermost occupied floors would exceed the targeted comfort levels without attenuation.
With additional study, the team determined that a pendulum-type tuned mass damper, sitting on the 54th level and suspended on 46-foot cables anchored two floors above to the framing of level L55M, would effectively control building accelerations. The 280-ton damper will keep wind-induced accelerations within the desired comfort levels—below those typically applied to residential buildings—for one- and 10-year wind events. The damper is also expected to provide a 10 to 15 percent reduction in drift for wind events with a mean recurrence interval of 10 years, and a 5 to 10 percent reduction for a 50-year return period.
Wind loads are not the only sources of vibration at 270 Park Avenue. The building shares its foundation with two dozen railroad tracks, therein subjecting it to intense excitation with each passing train. At minimum, several trains pass beneath the building every hour, and even more during rush hours. Severud engineers worked with RWDI to tackle the vibration demand, starting by developing an extensive vibration monitoring protocol and an initial input forcing function.
Using an analytical model of the Union Carbide building, the trial forcing function was applied and its response predicted. The modeling accounted for the subgrade modulus of the supporting rock, the travel path of vibrations from the track support framing to the building foundation and up through the building columns, and the proportion of the building mass participating in the response.
Analysis predictions were then compared to measured responses in the building. Using the observed measurements, the input forcing function was recalibrated accordingly and re-applied to the analytical model. After more than 150 iterations, a forcing function that produced responses in good agreement with measured vibrations was established and used as input to an analytical model of the new building to assess its anticipated vibration performance. Subsequent field measurements in the new building revealed a response to train-induced vibrations suitable for sensitive lab equipment at the ground floor, with significant reductions up through the tower.
Steel Innovations
Collaboration between Severud, construction manager AECOM Tishman, and steel contractor Banker Steel—based on close relationships strengthened during their work together on One Vanderbilt Avenue—led to significant improvements in the structural steel fabrication and erection. This was especially true for the Tabletop, a complex sub-structure that posed several logistical challenges and created the critical transition from foundation to office tower that made the project possible.
Tabletop connections, where at each node up to five massive members converge at a single point, benefited greatly from the steel contractor’s involvement. The conventional approach is to create nodes using welded plates, but that presented daunting constructability issues, mainly due to large, multi-pass welds and the likelihood of heat distortion. The potentially unfavorable aesthetics of the exposed connections were an additional liability.
Instead, the team proposed nodes fabricated from forged steel to reduce fabrication issues and better accommodate the three-dimensional stress field acting on the nodes. It is a brute force solution—the forgings are essentially huge blocks of solid steel—as well as a sophisticated one. Using the results of advanced finite element modeling that determine detailed 3D stress distributions, metallurgists at fabricator Ellwood Specialty Steel chose an appropriate alloy and proscribed a process of heat and mechanical treatments to fabricate weldable nodes that safely transmit high stresses on multiple axes.
The plate girders that form the backbone of the Tabletop are the building’s largest single elements. Spanning the length of the building, the plate girders are 25 feet deep—the full height of the second floor. Their flanges are 5 feet wide and up to 8 inches thick and their webs up to 6 inches thick. Due to their immense size and stiffness, deflection of the plate girders is negligible and cambering was not necessary.
Their total weight is on the order of 1,800 tons each, so the girders were divided depth-wise into three stacked sections that were fabricated in lengths that could be shipped upright, lifted into place, and field-bolted together. Many web penetrations were needed for doors and mechanical systems. The larger openings—greater than half the depth of the section—were only partially cut in the shop to maintain stability during transport. Once erected, the cuts were completed and the waste removed.
The erection plan developed by AECOM Tishman and Banker was perhaps most instrumental in the timely construction of the Tabletop. The transfer system’s two longitudinal girders and rows of fan columns create three natural east-west traffic lanes through the site. Banker Steel placed crawler cranes in the north and south lanes, which could pick up and place members delivered via the center lane via Madison Avenue—the only delivery access allowed.
Temporary elevated runways and a protection platform were designed and installed starting at the west and progressing east. Working independently, the cranes erected the fan columns; working in tandem, they erected the transfer girders and then the framing between the girders. This allowed erection to begin while demolition of the Union Carbide building and construction of the foundation walls were still in progress.
By the time the cranes reached mid-block, demolition and foundation work had been completed and the cranes continued east to Park Avenue. From there, they backed out the way they came in, erecting the framing between the fan columns and transfer girders and setting the four tower cranes that would erect the remainder of the building. Above the Tabletop, steel erection proceeded as if for a typical building. As a result of this ambitious plan, the building topped out ahead of schedule.
Sustainability Features
JPMorgan Chase envisions 270 Park Avenue as a model for the 21st century workplace, with sustainability features intended to achieve a Platinum certification in USGBC’s LEED program. The building’s infrastructure will be powered entirely by hydro-electricity sourced from a New York State supplier and will produce zero net operational emissions. The building will also feature best-in-class air quality, intelligent sensor-based controls, efficient water usage, and high-performance glazing.
Its construction employed a high proportion of low-carbon materials, including concrete that substituted ground glass pozzolans (GGP) for 40 percent of the cement in all structural concrete except the 16,000-psi mix. Use of locally sourced GGP in 52,000 cubic yards of concrete saved about 5,000 tons of embodied carbon and diverted more than 28 million glass bottles from landfills, as estimated by the GGP producer. The ultra-high-performance concrete contained about 60 percent supplemental cementitious material in the form of ground granulated blast furnace slag and fly ash.
The steel reinforcement in the concrete is made from nearly 100 percent recycled steel while the 94,000 tons of structural steel framing contains over 90 percent recycled material. Remarkably, 97 percent of the demolished Union Carbide building was reused, recycled, or upcycled.
Conclusion
Constructing a high-rise office building in New York City’s dense urban environment is difficult under the best of circumstances. Building one where a high-rise office tower already exists is even more challenging. To attempt to do so above active railroad tracks borders on the impossible. But with thorough study, extensive analysis, and enthusiastic collaboration, JPMorgan Chase and its experienced design and construction team was able to pull it off—without significantly disrupting or altering the trains below. The building is expected to be completed in 2025. ■