Gaining Urban Space: Platforms Over Rail Yards
Code Compliance
Another key issue with platform projects is determining which codes and standards apply, which is not so straightforward.
For example, Robbins asks, “If you build a deck over a railyard, does that make the deck a building, so then the building codes apply? Or if there’s a building that goes through that deck and anchors into the ground, how much of the deck around the building is counted as part of the building?”
This is a grey area with a lot of ambiguity and needs to be carefully evaluated on a project-by-project basis.
Take Hudson Yards. Here, the trains are an Metropolitan Transportation Authority facility that is governed by the New York State Code, in addition to other rail codes set by the Federal Railway Agency. However, the buildings on the site are all governed by the New York City Building Code.
“While the codes are similar and have similar performance goals, there are differences and all parties need to be aligned to avoid conflicts between codes and requirements for the projects,” Gottlieb says. “Making sure that everyone is aligned on which codes the project is following and the critical overlaps is important to the success of the project.”
The sheer number of regulatory documents involved shows the extent to which codes impact design requirements. Ultimately, the platform must satisfy all applicable codes, regulations, and requirements that include, among other things, building, transportation, railroad codes, fire, smoke exhaust, security/blast, and train impact regulations. “Sizes of structural members, their location within the yards, and sometimes even their shape are all affected,” Chan says.
In addition to the issue of codes, these overbuild projects must address a few unique design requirements. For instance, the platforms need to account for heat buildup from the trains. In order to address this for Hudson Yards, an extensive CFD analysis was conducted, and passive air intakes were located and designed to allow the heat buildup to stay within acceptable limits. The heat is then dissipated through this ventilation; three fan plants exhaust the air while three plants provide fresh air to the facility.
The decks are open on the sides, providing some fresh air, “but you still need the supersized fans hung on the ceiling of the deck to help move the air around and provide the ventilation,” Robbins adds.
Maximum and average temperatures of the structural elements were also derived from the CFD analysis, which, in turn, impacted the structure’s fire protection design, Smilow adds.
Another unique issue is emergency egress. In the planning and design, the building team must ensure there are multiple ways that people can exit from under the deck to the surface.
Designers must address the issue of stormwater retention. For another project where FXCollaborative performed a feasibility study, the rail yards’ locale required the proposed project to conform to stricter stormwater standards. Consequently, the design had to incorporate stormwater retention tanks. Such tanks tend to be fairly large and can encompass a significant part of the infrastructure.
The Future of Platforms
With urban population growth not anticipated to slow down any time soon, urban planners and designers anticipate that platform building over rail yards and transportation corridors will really take hold.
In fact, Estevez sees a new set of factors converging. City and state agencies have realized the value of leasing the air space above their properties to private developers; railyards are being sought as a way to renew cities and turn a profit; and the initial investments, risks, and logistics of these projects are starting to make financial sense.
“I think this is going to very much be a growing area,” agrees Robbins.
While these initial overbuilds will struggle with this new way of developing real estate, like any new venture, the more it’s done, the more efficient it will become, and the less costly it will be.
“These current projects are building a knowledge base, so it will become a little easier and more feasible for future projects,” Robbins says. “My hope is that it changes the way some of the transit companies who own large amounts of real state start to think about their real estate and the integration of development and infrastructure.”
SUNNYSIDE YARD
As New York’s Hudson Yards massive decking project moves along, another major metro project may not be far behind. In early 2017, the New York City Economic Development Corporation (NYCEDC) and Amtrak, along with several other agencies and consultants, released a comprehensive feasibility study for Sunnyside Yard in Queens. A master plan is now in the works.
Image courtesy of Sunnyside Yard Feasibility Study
The Sunnyside Yard project hopes to deliver 180 acres of new space with up to 24,000 homes, 19 schools, and 52 acres of public space on top of the rail yards.
With an anticipated population growth of 80,000 people to the area within the next two decades, the plan intends to deliver 180 acres of new space with up to 24,000 homes, 19 schools, and 52 acres of public space on top of the rail yards.
Zooming in to structural details, the study delineates the following:
- Structural steel construction is preferred for the deck, as it is lighter than precast concrete and therefore easier to maneuver and install in congested areas.
- Structural support walls or columns must be located outside of required railroad track clearances.
- Deck/platform depth—vertical thickness between upper surface and underside—will vary between 9 and 16 feet.
“In the study, we found that at five stories, around 60 feet tall, you could support that with a platform, but taller than that, you really need to have the transfer truss in the building,” explains Jack Robbins, AIA, LEED AP, partner, director of urban design, FXCollaborative, New York.
Image courtesy of Sunnyside Yard Feasibility Study
This proposed steel deck truss for Sunnyside Yard shows a typical height and span.
Furthermore, for these taller buildings, the study recommends:
- Require full support walls at track level.
- Orientation with the long axis perpendicular to the direction of the tracks, with support walls running between tracks, in order to provide adequate resistance to wind loads.
- Spanning three to four lines of columns, depending on tower length/height.
- A substantial steel truss—a mega-transfer truss—in the building podium to transfer the loads to support walls. The depth of the steel deck truss is anticipated to vary from 9 feet for shorter spans to 16 feet for spans greater than 150 feet.
“With the limited structural supports at nonuniform locations, the mega-transfer system situated at podium levels above the deck will allow towers of various sizes and geometries to be located independent of the podium structure, as if they were supported directly on terra firma,” says Yefim A. Gurevich, senior vice president, building structures, WSP, New York.
“The concept of mega-transfer trusses presented in the feasibility study is a way to balance the structure of the platform with the towers. This allows for a lighter less expensive platform, but it also provides flexibility by leaving the final layouts and transfers to be part of the building development,” adds Eli Gottlieb, managing principal, Thornton Tomasetti, New York. “In some cases, the platform could be designed with a deck that can support light loads, with strong columns to support the buildings. Then a transfer truss could be built as part of the building to support the building on the columns.”
In terms of the spans required for the buildings’ varying heights, the study delineates the following:
- Low-rise buildings of up to five stories can be located on deck spans of up to 150 feet with no mega-transfer truss required. Longer spans of up to 200 feet can technically be achieved at a cost premium.
- Residential buildings up to 14 stories and commercial building up to 17 stories can be supported on spans of up to 145 feet.
- Residential and commercial buildings between 33 and 43 stories can be supported on spans up to 115 feet.
- High-rise towers up to 69 stories can be supported on spans of up to 85 feet.
For wind and seismic loads, the study recommends tuned slosh dampers.
Overall, Gurevich points out that Sunnyside Yard, with its multiple train operations, creates a situation where the track layouts are nonuniform in nature. This means there are limited locations for vertical structure and large deck spans.
“The limited touch-down locations create the need for major structural transfers of building loads above deck,” he explains. “This nonuniform structural grid also creates additional challenges when using gantry systems for erecting deck over the operating tracks.”
Furthermore, the feasibility study notes that installing deck over the Main Line tracks and other critical tracks will be a constructability challenge, requiring multiple tracks out of service, large cranes, and significant advance planning.
One way to reduce risk, and the length of track outages, could be to incrementally launch the deck from previously constructed sections, rather than exclusively using cranes.
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