Newfoundland is due for completion in 2019. The 220m building will have 62 floors in total, of which 57 are for residential built-to-rent apartments and the remainder will house the plant room, restaurants, a gym and a residential play space. Our client is Canary Wharf Contractors Ltd, the architect is Horden Cherry Lee Architects and the detail architect is Adamsons Associates Architects. The Newfoundland project team for WSP comprises of project directors Kamran Moazami and Jack Adams, associate engineer Chris Gosden. The project has benefited from support of our global specialists from WSP New York to WSP New Zealand. Steve Bosi and Rimmy Vij are also providing support from WSP facades.
We talked to project associate, Chris Gosden, about how the challenges of this unique building called for a structural design solution that both enables and influences the architecture.
The Site is the Project’s Greatest Challenge
“The architects were very keen for the building to be centred at the end of the body of water that separates it from the station. The problem is that the tunnels for the Jubilee Line are perfectly aligned under the site. As they converge towards the station they create a ‘V-shape’ under our building, limiting our options for piling in the narrowing space between the tunnels.”
“Because it was to be built above tunnels, the construction had to be relatively light-weight, and we also had to find a way to transfer the building’s loads to the limited locations between and on either side of the tunnels where we could actually create foundations for the building. Our solution was to design an external diagrid, which allowed us to transfer the forces, and is an inherently stable structure for a slender building.”
The Banana Wall Challenge
“Constructing the basement was sensitive work. The Eastern side of the building basement lies behind a Grade 1 listed dock wall called the Banana Wall because of its shape in cross section. The secant piles which surround the basement box to keep the water out are positioned right up to the back of the wall, and we were acutely aware of the need not to damage it in any way. The Banana Wall was built at the start of the 19th Century as part of the creation of the docks.”
Watch our Hidden Marvels animation explaining how we overcame the site constraints.
No Room for Error
“If working behind that area of water was tricky, piling between the underground tunnels was even more difficult because we were having to go so close to them. Any damage to the tunnels risked disrupting the Jubilee Line which is vital to London’s transport network as some 100,000 plus people commute to Canary Wharf each day. The contractors would bore down to just above the level of the tunnels and then, when the tube was closed at night, people would walk through the tunnels to visually inspect them for any damage. Once they gave the all-clear, the contractors could continue boring past the side of the tunnels. As structural engineers we were pushing the boundaries to the limit in an effort to achieve the most efficient design. We wanted the piles to be as close together as possible to minimise the distance the raft had to span over the tunnels.”
Efficient Hybrid Building
“The core rose quite rapidly, with the diagrid structure following on closely to provide structural stability. Within the diagrid we have used different types of construction to create the floor plate. On the intermediate floors between the nodes, we have a concrete post-tension solution which allows for thin slabs and reducing the amount of reinforcement. At the node floors we have a steel beam solution with pre-cast units creating a deck between the beams.
Because of the building’s diamond shape and the geometry of the diagrid we have focal points at the nodes which cause forces to kick out from the building. As a result, we have to tie the building back in, and to do this we have engaged the whole structure, sharing the load between the perimeter tie beams, beams that tie back into the slab, and slab diaphragm and its structural topping, which is extensively reinforced, all creating a stiff disc.
Although none of these techniques are unique, bringing all the elements together makes for a very innovative solution resulting in a hybrid building that is very efficient.”
The node floors have been constructed using precast concrete slabs. This creates a platform from which to build the next 4 floors of the diagrid but it also separates the work above from the construction of the intermediate floors below. This means that a faster construction can be achieved. The intermediate floors are formed of post-tensioned concrete. The thinner slabs help to reduce the total self-weight of the building.
The Banana Wall
This is a section of the former southern wall of the West India (middle) Export Dock in East London, built between 1803 and 1806. A survey in 2001 revealed the skilful engineering involve in the wall’s construction, the main brick build incorporating a curving or banana-shaped section both for structural stability and to accommodate the profile of ship’s hulls. It is the earliest known example of reinforced brickwork.