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The only way is up: Why building above rail lines could be the future of city building
Elevating new buildings above existing transport infrastructure is an increasingly viable way of unlocking commercial value from previously undevelopable properties, a leading engineering consultant has told CLAD.
Ian Washbrook, associate at Entuitive, believes that innovative new technologies and engineering solutions can ensure downtown areas continue to develop even as available sites become more scarce.
The firm’s Canadian office, which Washbrook leads, is currently building Calgary’s New Central Library above the city’s LRT rail line. The half-moon shaped structure, just east of City Hall in East Village, has been designed by architecture studios Snøhetta and Dialog to resemble a modern yet graceful ship “sailing into the future.”
Work is being completed in phases so as to minimise disruption to the rail network, which will run below the new structure.
“At grade transportation corridors, such as rail or rapid bus lines, slice cities in half,” said Washbrook. “Having the opportunity to build above these helps connect neighbourhoods and build vibrant communities.
“Calgary Municipal Land Corporation (CMLC) recognised the library would be a fantastic addition to the city’s East Village, and had the vision to see this underutilised land transformed into one larger, more valuable property.
“Working with Calgary Transit on design scenarios for a tunnel extension constructed with a building above, it became clear this was a feasible approach from operations, safety, and budget perspectives. The tunnel extension comprises close to 40 per cent of the overall footprint of the New Central Library.”
Washbrook told CLAD that retail developments are among the most feasible projects to span across tracks, as noise disruptions are less problematic for shops than with other types of building, but added that “hotels, museums and theatres are also physically possible, as long as base isolation is studied by an acoustic consultant so that airborne and structure-borne vibrations are kept at a tolerable level.”
In addition to the Calgary project, Entuitive are also building a platform over New York’s Penn Station in Manhattan West – reclaiming a hectare of land and spanning 240ft over the busiest rail corridor in North America, including 15 active train lines. The site will feature a public plaza, three high-rise commercial towers and a hotel.
Meanwhile, urban planners in Toronto are considering a proposal to build a 21-acre deck park over one of the busiest sections of the city’s rail corridor.
Why was the decision made to build Calgary New Central Library above the rail line?
The library had long outgrown their existing space, and began looking for a new home with the functional spaces required by a modern day library.
The building is now under construction on a parcel of land above Calgary Transit’s Red Line rail corridor, which exits and enters a tunnel extending from Stampede Station to 9th Avenue. The tunnel was constructed in the early 1980’s to enable the LRT infrastructure to cross the CP Rail east-west rail corridor. For many years, the land surrounding the rail corridor served as underutilised surface parking lots. Two small oddly shaped wedges of property on either side of the tracks were not overly appealing for commercial or residential developers given limited size and inefficient configuration.
Entuitive performed an initial study for CMLC leveraging our experience unlocking land use opportunities above and next to transit. Entuitive’s precedent project was the Manhattan West Platform in New York City, which created an additional 2.6 acres of functional space, enabling the developer to construct a 5.4 million sq ft office development in west Manhattan.
What is innovative about this approach?
Constructing a building over an active LRT line had never been done before in Calgary and several innovative engineering solutions were employed.
We had to fast-track the encapsulation design and construction before the final design of the New Central Library building was complete. The completed encapsulation also served as a temporary construction barrier protecting the trains from construction activity above.
To speed up the process and eliminate shutdowns, we fabricated precast wall panels off-site, which enabled a one-sided form which acted as a guide for the placement of permanent encapsulation wall reinforcement. The wall panels served as safety barriers between the busy rail corridor and the construction workers.
A roof system was selected that was quick to install during a weekend shutdown. Again, precasting the roof framing double tees system saved valuable time. They were also the most cost effective precast section, and the lightest section to install. Once the encapsulation walls were cast and ready to accept the roof framing precast double tees, the installation of approximately 150 meters of roof panels only took approximately 30 hours and was scheduled over a long weekend shutdown.
Having to work within strict time restraints meant that optioneering of the library building had to be performed as the construction of the encapsulation took place. Load assumptions were made for the foundations of the encapsulation to support the load of the library building above.
We worked with the curve of the LRT tracks to inform the shape of the building. Large steel trusses were designed to span across the encapsulation, allowing for a column free main entrance which allows for the building to cantilever at the north tip, directly above of the tracks.
What were the biggest challenges?
The design and construction sequencing was intricately planned to maximize the revenue hours of the LRT line, and to minimise the number of shutdowns. Calgary Transit trains operate from roughly 5:00 AM till 1:00 AM. With approximately 1.5 hrs needed to power up and power down the system, construction workers had only a 1-2 hour window to work within the clearance envelope around the traction power overhead (OLS) line system. The innovative design allowed for most of the construction to take place outside of the highly electrified zone.
Existing soil conditions consist of 3m of fill on top of 5m of native gravel on a bedrock comprised of silt stone. Shallow spread footings would have required extensive excavation, and the risk of undermining the rail corridor. Large 4’-6’ foot diameter piles were augured into the bedrock. To achieve the adequate foundation resistance, many of the piles had to be advanced 18m into the rock.
How will the library adapt to the noise of the railway?
We were fortunate enough to work with a tenant that currently has their main branch adjacent to the LRT rail corridor. They are used to the rumble of the trains. The library was not designed to be fully acoustically isolated. Only certain quiet spaces such as reading rooms and meeting rooms were sound-proofed. The cost to isolate the entire building would have been cost prohibitive. To isolate the tracks was a non-starter given that the tracks would have had to be pulled out and new base isolators installed, which would have resulted in too much down time for an extremely busy rail corridor.
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