The crossrail project in London is known to be the largest transport project in all of Europe with 9 new stations and 42 km of underground tunnels. The location of the stations and the rail routes were fixed after multiple studies and surveys, and so the location for the Canary Wharf station was fixed in the waters of the North Dock within the existing commercial port complex. The cross-rail station improves the connection to the rest of London and further east.
DESIGN
The elegant glass structure with its timber lattice roof and decks extending onto the water gives it the sense of a gracious ship moored in the historic port. The six-storied structure was conceived as a lively new community facility complete with retail, cafes, cinemas, public amenities, and a rooftop garden. Most of the Canary Wharf cross rail station lies below water with only two floors visible above water that links itself to the city through vehicular bridges at the street level and pedestrian bridges at the promenade level. The four levels above the dock bed are dedicated to public activities that blend seamlessly with the community facilities around the station, while the subterranean levels that extend up to 18m below the dock bed are dedicated to the transport facilities.
The roof is a 4000 sqm landscaped garden that houses an array of plant species native to historic British trading destinations, hence displaying the nautical legacy of the dock as a historic trading hub. It houses community spaces used by schools and other organizations and has developed into a vibrant public place for the city.
The use of wood sits well with the historic character of the place, with its versatile nature and organic appearance. At night, the lattice is illuminated from below while the translucent shell gives the structure a welcome glow. The openings on the sides allow views of the water and the activities around.
STRUCTURE AND MATERIALS
The most imposing part of the structure visible is its timber diagrid shell. The 310m roof structure with the timber lattice and its infill air cushions cantilevers 30m over water on either end and is the longest timber structure in the world. Despite the length of the structure and its curved form, the lattice consists of only four timber arches.
The lattice is a triangular grid with straight wooden members joined together by innovative steel nodes to generate the curve. The lattice is a design-cum-engineering feat and was designed with the help of parametric software. Between the members are air-filled Ethylene tetrafluoroethylene (ETFE) plastic cushions that are lighter than glass. The spruce glulam lattice not only sets a contrast from the adjoining steel structures but also weighs lighter than an equivalent steel structure.
Six members meet at a node resulting in 300 different node types depending on the angle of the members and the loads they carry. The structure was analyzed and designed for everything from its timber quality, nodes, strength, internal pressure, forces, and dimensions.
The construction of the structure was from the dock base by the top-down construction within a cofferdam with tied-back retaining walls on three sides and an existing retaining wall on the fourth. About 100,000 cubic meters of water had to be drained off the dock before the commencing of construction. The retaining walls consisted of 310 interlocking tubular steel piles installed using the Japanese Giken silent piling system. The project won the 2011 Ground Engineering award for technical excellence for its innovative design and construction techniques.
SUSTAINABILITY
Every aspect of the station from the materials to the spatial organization was designed keeping the sustainability aspect in mind. The spruce glulam is a PEFC-certified timber sustainably sourced. The waste timber was used in the Wiehag’s power station at the Altheim factory, hence converting it to a useful resource. The lattice structure is so designed that the timber members can be easily disassembled and reused or made into bio-fuel at the end of its life.
The materials are chosen to reduce the structures dead load to a minimum which in turn reduces the capacity requirements of the foundations and other structural elements. The air cushions are a highly insulating material that keeps the station functional and the rooftop garden usable all year round while providing a favorable microclimate for the plants.
The translucent ETFE plastic cushions keeping the spaces naturally lit. The public spaces are naturally ventilated in addition to the other passive cooling strategies adopted. The rooftop garden is made open to the sky by omitting out air cushions, hence allowing sunlight and rainwater in for the plants. Along with rainwater harvesting, sustainable strategies such as grey-water recycling have been applied.
