Editor’s Note: This article is based on an interview with Andrea Travani conducted by Sue McCraven, NPCA technical consultant.
By Andrea Travani, P.E.
Containing a bustling population of more than 8.5 million, New York City has about 28,000 people per square mile – a concentrated, growing mass of humanity greater than that of Los Angeles and Chicago combined. NYC is home to more billionaires than anywhere else in the world. Many live part-time in luxury Manhattan apartments that can run $50 million or more.
With buildable land scarce in NYC, the city’s premier real estate developers were in search of a solution to maximize the limited space available. Looking out over the undeveloped Far West Side and the Hudson Yards District, they discovered a simple solution. All they needed to do was look up.
Enter precast concrete and the Manhattan West Project, where a huge, custom-built Launching Gantry (LG) is positioning 2,400-ton, 240-ft-long precast/post-tensioned beam spans above 15 live rail lines and their electrified power lines. These beams will support a public plaza and parking structure between two high-rise buildings.
From steely plans to an unprecedented precast solution
Brookfield Office Properties, owner and developer of the Manhattan West Project, contacted Rizzani de Eccher USA (RdE USA) seeking a solution to close a big gap in the middle of their 7-million-sq-ft development site by somehow spanning this air rift with a platform above bustling, high-traffic-volume railway tracks. Brookfield executives had observed the efficiency of the LG RdE USA used to erect haunched precast bridge segments in rebuilding the old, steel Roslyn Viaduct in Long Island, New York.
Originally, the platform design called for structural steel. After collaborating with several consultants on an innovative new concept, RdE USA presented the owners with the following alternative solution:
- Use precast bridges to span the entire opening.
- Erect the precast bridge segments with a custom-built overhead LG.
- Eliminate the need to place steel columns in between the railroad tracks below.
Erecting a monster beam at record length
NYC is home to many brilliant engineering ideas. Fittingly, 2,400-ton segmental beams are being placed at a record length of 240 ft – during the early morning hours – all 55 ft above live tracks that run in underground tunnels to Penn Station.
Brilliant engineering ideas depend on equally innovative construction designs and tools. The success of the Manhattan West Project hinged on two important components:
- The ability of DEAL, a subsidiary of RdE USA, to manufacture a very high-tech piece of LG equipment with the capacity to smoothly place 16 beams in position; and
- The skills of McNary Bergeron to design a precast concrete beam that could accommodate 100 tons of post-tensioning strands inside.
Comprised of 1,100 tons of steel with a capacity to lift 3,600 tons, the LG has a 90-ton winch for handling the individual segments before they are epoxied and post-tensioned into a single, giant beam. Every component was designed and manufactured in Italy and broken down into more than 90 containers to allow oceanic transport to NYC.
Before placing the first span, some New Yorkers and other contractors were expecting a dramatic scene: perhaps loud impact noises or the thrill of precariously swinging loads. But when RdE USA erected the first beam, it was so smooth, silent and precise that many observers on site were somehow disappointed.
Launched infrastructure and saving with precast
The assembly process is very similar to other sequential span-by-span bridges that use an under-slung LG. Here, the difference is that a platform is being built, so there is no need for a gantry that launches from pier to pier. Rather, a machine moves sideways to place one completed bridge span adjacent to the next. This is a unique setup in Manhattan and one that could be very useful in any situation where, because of busy train tracks or roadways, urban developers are not able to maximize all the potential real estate space.
The most important feature of this type of project is early collaboration during the conceptual phase on construction alternatives that allow placement of columns, slabs, steel or segmental bridges to maximize design flexibility. In particular, solutions that use precast concrete elements speed up construction and, considering the significant labor rates, keep costs down.
The LG solution seems to have been the only economical way to develop these parcels of land. In fact, Brookfield acquired the property in the early 1980s, and it remained undeveloped for decades due to the presence of critical rail traffic.
Jersey Precast succeeds at complex beam geometry
Because of all the geometry control required, precasting segments such as these for the first time is not easy. As a result, RdE USA sent some of its engineers to the precast plant to work side-by-side with Jersey Precast personnel to ensure an accurate transfer of knowledge for a quality job.
McNary Bergeron designed the precast bridges. Each bridge consists of 37 to 39 match-cast segments individually trucked on site and assembled over the under-slung bed. Once the segments are epoxied, post-tensioned and grouted together, the giant beam is lifted and erected into its final position.
Challenges for platform project manager
Despite the overall success of the project, there is always room for improvement. For example, the temporary post-tensioning bar configuration was a real challenge because having narrower-than-usual precast segments presented some difficulties in the installation and removal of the rods.
Another significant challenge is the engineering involved in coordinating the design of the bridges and equipment. Because this is such a unique structure, an innovative, seamless approach is required to make it work.
The logistics of the project are also complex, with work taking place on a staging area effectively the size of a postage stamp (250 ft by 90 ft) in the middle of Manhattan. Assembling the LG meant trucking in more than 90 very large and heavy containers to a small, confined area where other contractors were also working.
RdE USA had significant interaction with SOM (the project architect) during the design phase. The most critical issues faced were related to creating openings in the platform to possibly allow future columns for the overhead buildings to touch down at the track level. The platform’s design is very sophisticated and these openings were particularly daunting because of the flow of stresses on the deck.
New urban frontier
Melisa Coley, Brookfield’s vice president of investor relations and communications, captures the amazing potential of this remarkable technology for major cities everywhere: “In a sense, it’s kind of Manhattan’s final frontier,” she said. “There’ll be lots of parks, lots of amenities, and the transportation is huge being right next to Penn Station.”
“This groundbreaking project is the first time that post-tensioned bridge segments have been produced locally in NYC,” said Arshad Afridi, COO of Jersey Precast. “Our association with RdE USA has been a source of valuable technical expertise, support and immense mutual benefit, and will continue to open up new opportunities for both firms.”
Perhaps a more important opportunity is the yet-unimagined infrastructure potential for urban frontiers across North America.
Andrea Travani, of Rizzani de Eccher USA, is the project manager for the Manhattan West Project in NYC. With master’s degrees in engineering and project management from the University of Trieste, Italy, Travani has extensive international experience in managing major transportation, bridge, rail and municipal projects, most involving specialized launching gantries.
The following video illustrates the steps taken to place each of the 56-ton precast concrete segments for the project.
Sidebar – Manhattan West Precast Platform Project
Overall Project: The Manhattan West Project leverages the power of a launching gantry (LG) to produce a precast/post-tensioned platform used to support a public plaza and parking structure between two high-rise buildings.
Platform Location: The Manhattan West Project is located between Ninth and Tenth Avenues and 31st and 33rd Streets and above Amtrak rail yard with 30 tracks that lead to Penn Station, in Manhattan, New York.
Manhattan West Owner & Developer: Brookfield Office Properties, NYC
Overall Project Construction Manager: Turner Construction Co., Headquarters: NYC
Manhattan West Project Construction Manager: Rizzani de Eccher USA, Bay Harbor Islands, Florida and Pozzuolo del Friuli, Italy
Precast Platform Design Engineers: Entuitive, Toronto, Canada
Precast Post-tensioning: Tensacciai, Milano, Italy
Launcher Gantry Designer: McNary Bergeron & Assoiates, Old Saybrook, Connecticut and Broomfield, Colorado
Launcher Gantry Supplier: DEAL, subsidiary of RdE USA, Italy and Florida
LG Operator & Platform Erector: Metropolitan Walters LLC, New York
Precast Concrete Segments Producer: Jersey Precast, Trenton, New Jersey
Platform Bridge Bearings: Mageba, Bulach, Switzerland
Drilled Caissons & Foundation Contractor: Posillico Civil & Drilling, Farmingdale, New York
Cast-in-Place Concrete: John Civetta & Sons Inc., Bronx, NYC
Superstructure Architect: Skidmore, Owens & Merrill, Chicago, Illinois
Lessor of space over Long Island Railroad/Amtrak Yard: NYC’s Metropolitan Transportation Authority