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Civil Engineering Magazine THE MAGAZINE OF THE AMERICAN SOCIETY OF CIVIL ENGINEERS

West Side Extraordinary

By Jared M. Green, P.E., M.ASCE, Shari Leventhal, P.E., LEED AP, M.ASCE, George E. Leventis, P.E., F.ASCE, Alan R. Poeppel, P.E., M.ASCE, and Konstantinos Syngros, Ph.D., P.E., M.ASCE

VIA 57 West is one of the newest skyscrapers in Manhattan, New York, as well as one of its most geometrically distinct and spectacular. The geotechnical and site civil challenges of the project were equally atypical.

Everyone knows what a typical New York City skyscraper looks like. The structure is tall and straight as it rises into the city's famous skyline. You can see these buildings in numerous photographs, reaching various heights, some featuring setbacks or other special architectural details but many of them sharing a roughly similar rectangular silhouette.

A striking exception is the sloping form of VIA 57 West, which is located at a site on 12th Avenue, between 57th and 58th streets, on the western edge of Manhattan along the Hudson River. A mostly residential building with retail at the base and an enclosed courtyard at its third level, the tetrahedron-shaped structure climbs at a sharp angle toward its maximum height of 467 ft—but only on its northeast corner. The other corners were kept low, just a few stories tall, to maximize the unobstructed river views both for its own tenants and those of a neighboring residential tower.

Representing "a hybrid between the European perimeter block and a traditional Manhattan high-rise," the form of the building shifts, depending on the viewer's vantage point-presenting a pyramid from one angle and forming a glass spire from another, according to the website of the architecture firm Bjarke Ingels Group (BIG), based in Copenhagen, Denmark, and New York. BIG designed VIA 57 West for the Durst Organization, of New York.

Other members of the mostly New York-based design team included SLCE Architects as the architect of record and Thornton Tomasetti as the structural engineer (see "A Different Angle," page 55). New York-based Langan was the geotechnical and site civil engineer. Hunter Roberts Construction Group, of New York, was the general contractor, and the Laquila Group, also of New York, was the foundation contractor.

S ix years. That's how long the Langan engineering team spent studying the VIA 57 West site before the first shovels broke earth. While the Durst Organization was exploring various developments to realize the highest best use of the parcel during those six years, Langan was busy overcoming numerous engineering challenges associated with the site and the distinctive shape of architect BIG's hyperbolic paraboloid design. Like the unconventional building design, the site itself was atypical because of its neighbors: a power plant, a sanitation facility, the heavily trafficked West Side Highway, and a residential building. The property was also located beyond the old Hudson River shoreline, was contaminated from years of industrial use, and had varying depths of bedrock.

The site is believed to have been traversed through its middle section by a northwest-southeast shoreline dating to roughly 1609. As a result of the marine environment, the site's native soil generally consists of sand and gravel outwash overlain by alluvial, soft, fine-grained organic silt. Still farther down, the bedrock underlying the site is predominantly gneiss from roughly 5 to 50 ft below the ground surface. The limits of the historic shoreline are evident on an 1836 map (shown at left). Since the first European landing in the New York area during the early 1600s, developers have pushed Manhattan's western shoreline farther out into the Hudson River numerous times; around 1880, these efforts included the site that would eventually be home to VIA 57 West.

More recently, the site was used for automotive and truck sales and service and housed several buildings. Langan investigated the subsurface while the site was being used to temporarily stage sanitation trucks before the demolition of those buildings.

To better understand the site's subsurface, Langan relied on information from 73 borings, six observation wells, six test pits, and 39 perimeter probes that were performed on or within 25 ft of the site. The large number of borings was needed to meet the New York City Building Code requirements for the footprint of the 110,000 sq ft site. More than 50 of the borings had been performed by another consultant in the early 2000s as part of an earlier site investigation. Langan followed up with an additional 12 borings and three test pits in January 2008, 14 shallow perimeter probes and three more test pits in September 2009, and seven borings and 25 shallow perimeter probes in July 2010. Langan also provided oversight of seismic cone penetrometer tests at 16 locations in September 2009 and July 2010.

The test pits were dug throughout the site to provide information that was used to design the perimeter support system for the excavation, as well as to determine the location of any below-grade boulders or other subsurface obstructions. Hollow-stem auger probes were employed along the site perimeter to search for old piers or marine obstructions that might interfere with the installation of the excavation support systems. Fortunately, the design team did not encounter any obstructions, and any foundations from the former buildings were excavated and removed during the construction of the new foundations.

The cone penetrometer probes and laboratory tests were used to perform a seismic study, which provided an efficient, cost-effective, and safe seismic design for the foundation and superstructure. The study consisted of developing bedrock ground motions specific to the site, performing ground-response analyses according to the current state of practice in the fields of seismology and geotechnical earthquake engineering, and recommending seismic design parameters for the structure.

Developing the site-specific bedrock motions consisted of:

  • performing a seismic hazard analysis to determine the bedrock acceleration response spectrum
  • collecting representative ground-motion time histories recorded during earthquakes
  • matching the recorded ground motions to the estimated bedrock acceleration spectrum

The site-specific ground-response analysis consisted of:

  • performing multiple one-dimensional wave propagation analyses using the developed bedrock input motions
  • performing two-dimensional dynamic finite element analyses to evaluate the impact of sloping bedrock within the site
  • developing a site-specific design response spectrum (a plot of spectral acceleration versus building periods) for use in the superstructure design

The conclusions of the study included the following:

  • The recommended design response spectrum was lower than the New York City Building Code general procedure spectrum for a site-class E site at all periods.
  • The corresponding recommended short- and 1-second-period design accelerations were 0.410 g , and 0.130 g , respectively.
  • The resultant design spectral accelerations along with other data indicated that the project would be considered in the New York City Building Code's Seismic Design Category C.

A portion of the structure's foundation system (one featuring spread footings bearing directly on bedrock) could be classified as Seismic Design Category B, which is less stringent structurally than Category C. But that part of the structure would have to have been separated from the remaining structure by a seismic joint at the foundation level. Rather than installing that joint, the design team decided to adopt Category C for the entire project.

After evaluating the subsurface investigations and the seismic study, Langan determined that the most suitable foundation system for the building should consist of multiple elements, including driven and drilled deep piles, shallow mat foundations, and individual column footings supported on the bedrock. The design of these elements was developed collaboratively by Langan and Thornton Tomasetti. The top figure on page 54 depicts the foundations and the site subsurface.

The building design coincidentally-and conveniently-worked well with the governing subsurface conditions. The tallest and heaviest part of the building is at the northeast corner of the site, which is also where the depth to bedrock is most shallow. Approximately 750 cu yd of rock was removed at this part of the site to accommodate the 6 ft thick concrete mat, which is founded directly on bedrock consisting of gneiss, schist, and granite. This material has a bearing capacity of 20 tons per square foot. The bedrock was line-drilled at the site perimeter to limit the potential for rock overbreak-the accidental removal of more rock than necessary. Because the bedrock was rather massive, additional bolting to maintain a stable, exposed, vertical rock face was not required.

In all, 574 driven piles were installed at the site. Each pile had a design compressive capacity of 200 tons and consisted of a 13.375 in. diameter closed-end pipe pile with a wall thickness of 0.48 in. These piles were driven to bedrock and then filled with 5,000 psi concrete. An extensive full-scale load-test program was performed to confirm the compressive, lateral, and uplift capacities for these piles. Originally, these driven piles were intended to support the entire building. But because of dewatering requirements, another series of drilled piles, or caissons, was also installed.

The dewatering system was required until the building had sufficient dead weight to resist hydrostatic uplift forces, which equaled the dead weight of several floors of the superstructure. Because the construction of those floors to counter the uplift forces would have taken several months, the design team decided to supplement the foundation with drilled caissons to account for the loads. These caissons were installed at strategic points to serve as tension-compression elements, which allowed the dewatering system to be turned off after the foundation slabs and walls were cast.

Ninety-three drilled caissons were installed, each with a compressive capacity of 200 tons and a tension capacity of 100 tons. Each caisson consisted of a steel casing socketed at least 1 ft into the bedrock. This casing had a 13.375 in. diameter, 0.375 in. thick walls, and a yield strength of 50 ksi. Beneath the casing, the 12.5 in. diameter rock socket was created with a minimum length of about 7 ft. The strength of the concrete fill was 6,000 psi, and the steel reinforcement consisted of a double-corrosion-protected number 28 bar, 3.5 in. in diameter, with a yield strength of 75 ksi.

Because of the use of various foundation elements and the fact that the depth to reach bedrock dropped off precipitously in some places near the center of the site, the project employed so-called transition elements, from the conventional spread-footing foundation system to the conventional driven-pile foundation. Working from a top-of-rock contour map developed from the borings, the design team determined that the zone in which the transition elements would be needed was about 40 to 50 ft wide and had a south-to-north westerly skew. The new building columns within this zone of transition elements were supported on concrete piers bearing on the bedrock. An allowable bearing capacity of 20 tons per square foot was used to proportion the sizes of these transition piers-the same bearing capacity used for the 6 ft thick concrete mat. 

The Durst Organization's emphasis on sustainability and green building practices was a major component of this project. Sustainability was even incorporated into the foundation design: the slag cement was made from 100-percent preconsumer material, and all the wire in the rebar chains-fabricated by New York-based Brooklyn Rebar-was melted from 100-percent recycled material, most of it postconsumer. The preconsumer/postindustrial recycled content of the project's cement also varied from 10 to 19 percent.

In late October 2012—during the superstructure design and foundation construction phases—Hurricane Sandy made landfall in New York City with a storm surge that flooded the most vulnerable waterfront areas. In many of these areas, flooding exceeded what was at that time the Federal Emergency Management Agency's 100-year base flood elevation, prompting developers to rethink mitigation strategies. The Durst Organization took a proactive approach to this project and directed the design team to account for future events of similar magnitude by going beyond what was required at that time by the building codes. While foundation construction was ongoing during and after the storm, flood-resistant design changes were incorporated into the foundation installation.

For example, a vertical waterproofed curb designed to resist water pressures from flooding several feet above street level was added to the design, and the entire foundation was waterproofed with a system from GCP Applied Technologies, of Cambridge, Massachusetts (formerly part of W.R. Grace). Waterproofing membranes were installed before and after concrete placement and before backfilling. Careful attention was paid to the installation of these membranes, especially in relation to the termination of the products at the penetrations for piles and utility point-of-entry locations.

The excavation support system for the eastern part of the site—where the bedrock was at its most shallow—consisted of concrete piers measuring 4 ft square in cross section and bearing directly on bedrock. Lateral support was provided by wood lagging boards installed within slots in the piers. The balance of the site perimeter was supported with an interlocking sheet-pile wall, its lateral support provided by external tieback elements that were socketed into the bedrock. The western third of the site does not have an underground level, so only a shallow excavated slope was used to support the excavation there.

Any contamination left over from the site's industrial past was remediated during the excavation work. The environmental cleanup effort was performed by another engineering firm, Roux Associates, of Islandia, New York, as part of the New York State Brownfields Cleanup Program.

During the construction of the foundations, Langan performed special inspection services for the client and in this role was able to make adjustments in the field that helped maintain the project schedule. Establishing and adhering to stringent health and safety standards during this phase was also important to the project's success. The design team adopted the contractor's safety program, which was designed to mitigate even the most minor injuries on the jobsite. This was accomplished, in part, by holding a full-day health-and-safety workshop for the design team, continually engaging workers to ensure that they were knowledgeable about the program's policies and procedures, and conducting routine safety walk-throughs.

Langan was also responsible for grading the sidewalks at the perimeter of the site and the portion of the street from West 57th to West 58th, paying close attention to the requirements of the New York City Department of Transportation and the Americans with Disabilities Act. Additionally, Langan designed sanitary sewer, water, and storm drainage, which were approved and permitted by local agencies. The stormwater management design incorporated building stormwater reuse and resulted in a reduction of stormwater sent to the city's combined sewer. Langan also designed and implemented a soil erosion and sediment control plan for the site.

Because of the unique shape of the building, the engineering team needed to develop an understanding of the sheet flow of stormwater from the sloping facade, which doubled as the roof when modeling stormwater drainage.

The construction of VIA 57 West began in July 2012, the excavation work began in January 2013, and the foundation concrete was completed in January 2014. The total foundation cost was $23 million. The project was completed during late 2016 at a cost of $468 million. The design team's extensive understanding of the site, along with its spirit of collaboration throughout the development process, contributed to the success of VIA 57 West, which has helped reimagine Manhattan's west side skyline.

Jared M. Green, P.E. , M.ASCE , is a vice president; Shari Leventhal, P.E. , LEED AP, M.ASCE , is a senior project manager; George E. Leventis, P.E. , F.ASCE , is a managing principal; Alan R. Poeppel, P.E. , M.ASCE , is a managing principal; and Konstantinos Syngros, P h. D ., P.E. , M.ASCE , is a senior project manager in the New York City office of Langan.

PROJECT CREDITS

Client: The Durst Organization, New York City
Architect: Bjarke Ingels Group, Copenhagen, Denmark, and New York
Architect of record: SLCE Architects, New York
Structural engineers:
Thornton Tomasetti, New York
Geotechnical and site civil engineers:
Langan, New York
Environmental engineer:
Roux Associates, Islandia, New York
General contractor:
Hunter Roberts Construction Group, New York
Foundation contractor:
The Laquila Group, New York

A Different Angle

By Robert L. Reid

The unique, sloping shape of the VIA 57 West building is formed from cast-in-place concrete from the single, partial basement level up to the structure's 34th floor; braced galvanized steel framing completes the structure up to its 44th-level peak. The building essentially wraps around the 25,000 sq ft internal courtyard that begins at the third level, the walls facing this green space with a series of cantilevered balconies arranged in a sawtooth pattern in plan.

The geometry of the building presented a number of structural engineering challenges to the engineers at Thornton Tomasetti-challenges "that are typically not an issue with rectangular residential towers," noted Robert Otani, P.E., LEED AP BD+C, M.ASCE, a Thornton Tomasetti principal who provided written answers to Civil Engineering questions

For example, the setbacks vary at each floor, and "there are column transfers on each floor level ... to conform to the overall tetrahedron geometry and sloping facade," Otani noted.

Moreover, there really is no roof to the building. Instead, the unitized facade is extended to the top of the building, forming a sort of combined facade/roof system. As a result, the structure features a "one-of-a-kind building facade/roof maintenance system that required significant structural coordination and interface," Otani explained.

Matching the proportions of New York's Central Park, the interior courtyard also created some unique challenges because its design included numerous level changes-the elevation varies up to 9 ft from the east side to the west side of the space-and incorporated various landscape design features, Otani noted. The solution involved a combination of floating slabs-on-grade on high-density, rigid foam to build up from the concrete deck and framed slab-on-metal deck that was supported on cantilevered concrete masonry unit walls, he explained.

The greatest structural challenge, though, involved the design of the lateral system, which featured core and shear walls and moment-resisting frames "to satisfy seismic demands and wind deflections given the uneven massing of the building, the added facades caused by the internal courtyard, and resolving the internal forces caused by creep and shrinkage for the very large floor plates at the lower levels," Otani said.

According to a Thornton Tomasetti project description, the building utilizes 10 in. thick, two-way flat slabs as well as a thickened 18 in. transition slab along the perimeter balcony setbacks. The slabs and columns are "integral to the lateral system" and resist almost one-third of the lateral wind and seismic loads, explained Otani. "The remainder of the lateral loads is supported by two concrete cores surrounding the elevator banks and by three concrete shear walls," according to the project description.

A high water table at the site was also a significant issue that grew even more challenging when the Federal Emergency Management Agency revised its flood maps during the design phase of the project. As a result, the western side of the site fell within the 100-year floodplain. This meant that integral flood walls had to be added to the design to comply with the new maps. "The flood walls were required at the western portion of the site, where the first-floor elevation is below the design water table," Otani wrote. Mechanical systems were also elevated above the floodplain, and the basement-level slab was designed to be 15 in. thick to resist hydrostatic pressure; grade-level slabs are 12 in. thick, Otani added.

Robert L. Reid is the senior editor/features manager of Civil Engineering. 

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