Space station hero

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Heron Quays DLR station looks pretty futuristic with its metallic hull and dramatic lighting. But what’s really innovative is how it and a six-storey building above the tracks were built without shutting down the railway. Project manager Graeme Tait reveals how it was done

The old DLR station made way for Alsop Architects’ striking design, complete with aluminium casing and columns to support the platforms

For thousands of commuters streaming through Heron Quays every day, the most striking thing about the station is its quirky design. It is like no other on the Docklands Light Railway with an aluminium casing slung beneath the railway tracks to form a ceiling for the concourse and entrance. Raking circular steel columns rise from the concourse to support the station’s platforms and the banks of escalators leading to them. Uplights, downlights and fluorescent tubes bathe the area in dramatic colour and highlight the stunning design.

Few commuters will know, however, just how difficult it was to construct the new station and a six-storey air-rights building above. The old station had to be demolished to make way for two high-rise buildings being constructed on either side of the tracks.

Graeme Tait, project manager at Canary Wharf Contractors, explains: “Erecting such a large structure over a live railway has never, to our knowledge, been done before in Europe.” Adding to the job’s complexity was that the station was being constructed at the same time as the buildings on either side. The two high rises were for Morgan Stanley and Lehman Brothers, with the latter wanting the air-rights building above the station as extra accommodation.

Living for the weekend

It also had to be done with limited closure of the railway: only three weekends, from 1am on Saturday until 4am on Monday, were allowed by DLR and the Railway Inspectorate. The only other time CWC was allowed to construct anything above the unprotected tracks was after the DLR stopped running each night. “We only had three hours, 15 minutes. There’s nothing like feeling under pressure,” quips Tait.

In just over two months, CWC and its trade contractors formulated an ingenious plan to construct a protective shelter for the station that would allow work to proceed unheeded on the air-rights building.

The way Tait describes it, the plan sounds simple.

It was, in fact, a carefully thought out strategy developed with the steelwork contractor, a joint venture between Victor Buyck and Hollandia. First, an elevated protection platform was built at the south end of the station concourse, above which large steel trusses would be placed straddling the railway viaduct. The platform was partially assembled in Greenwich, south of Canary Wharf, and ferried by barge across the Thames to a mooring next to the project.

One of the three DLR weekend closures was used to install the protective platform and form a working deck. The next operation involved placing the trusses, which would provide temporary support for the air-rights building, on runway beams either side of the protection deck. Victor Buyck-Hollandia transported the trusses, which weighed up to 40 tonnes each, from the fabrication plant in the Netherlands by an ocean-going barge. Again, the barge was moored next to the site.

Once the trusses were installed on the runway beams, the launch process commenced. It started with the leading truss being jacked along the runway beams, which were supported by rows of concrete columns either side of the station. Steelwork beams and braces were then attached to unite the leading truss with the second truss. Profiled metal decking was stud-welded on top. When this was done, the two-truss assembly was jacked farther along the runway beams to allow steelwork and decking to be connected to the third truss. And so the work continued until the assembly to protect the rail track and station area was in place.

When the launch process was complete, the floor deck immediately above the trusses was concreted to form a physical barrier to the railway below. This, and strict lifting controls, made it possible to erect the steel frame of the air-rights building.

Erecting such a large structure over a live railway has never been done before in Europe

Again, CWC had to overcome complications to erect the floors. Working restrictions imposed by DLR meant the end bays of the building could only be constructed in the middle of the night. Also, the cranes had their load capacity reduced by 25% and steelwork elements located close to the railway viaduct had to be slung with secondary safety shackles attached.

After the lower five floors were formed, the next task was to erect the jumbo trusses to form the structural floor from which the building would eventually be hung.

A fully assembled truss weighed in excess of 90 tonnes, which was far beyond the lifting capacity of the tower cranes, so it had to be fabricated in segments. This meant substantial temporary props were needed to support the segments while they were being welded together. The welding was a big job: the flanges of the trusses were about 100 mm thick and had to be full-strength welded.

CWC also had to install a two-piece plate girder that linked the trusses to an adjacent tower block. Due to their weight, the girder elements were erected late at night under supervised lifting. With supervisors from the DLR and crane supplier Hewden Stuart in attendance, the lifting restrictions were removed from two tower cranes so they could each handle a piece of the girder. The two elements were then spliced together.

With the jumbo trusses fully connected to their supports, the delicate task of transferring the load of the air-rights building from the temporary trusses to the jumbo trusses began. Jacks beneath the temporary trusses were lowered until the building was left hanging from the jumbo trusses above. Only then could the rest of the floors be concreted.

Throughout the entire construction process, a series of checks and balances were undertaken to ensure no part of the structure was overstressed until the jumbo trusses could do their job.

Despite the complexity, the air-rights building and the station took just 17 months to get from build concept to completed structure. “All in all,” says Tait, “I think it went well. That’s because we planned it meticulously, we built it on paper before we built it on site and our contractors have the experience and track record to meet the challenges of this project.”

Lehman Brothers air-rights building

Executive architect Adamson Associates
Engineering consultants Tony Gee & Partners, Yolles & Partners
Contractor Canary Wharf Contractors
Steelwork contractor Victor Buyck-Hollandia joint venture

Heron Quays station

Architect Alsop Architects
Engineering consultant WS Atkins
Fire engineering Arup Fire
Contractor Canary Wharf Contractors
Steelwork contractor Robert Watson

WHARFpeople - Clare Wright

Clare Wright sees her job rather differently from most construction lawyers. She believes her role is to help smooth construction rather than getting entangled in disputes, claims and legal action.

Wright, one of four lawyers working in-house for Canary Wharf Contractors, left private practice to join the company in 1998. She says: “I was quite happy where I was, but when I came down here it was too exciting to say no.”Wright is a non-contentious lawyer specialising in handling contracts between CWC and its tenants, trade contractors, suppliers and consultants. She says the gulf between her previous and present roles couldn’t be wider.

“When I was in private practice, I had to be very legalistic and say ‘This is the law, this is what you have to do’. Whereas here, I’m much more likely to say: ‘These are the legal options, here are the ones that are less risky’ and then let the commercial people decide.

“We are part of the chain that builds buildings and we have to be pragmatic, not legalistic. Normally, when someone says, ‘I’ll just bring in the lawyer,’ people start to panic. It’s not like that here.”

Wright acknowledges the scepticism that some have about construction lawyers, adding with a laugh: “I’d like to think we are welcome.”

CWC uses its own bespoke suite of contracts (some of which are based on JCT or NEC forms) but will tailor them to suit specific needs. “Most of the time, it is a question of explaining the contract, not negotiating changes,” she says.

Clauses such as those governing adjudication were in place at Canary Wharf long before they became a legal requirement. “We’ve always had the non-dispute ethos, the come-in-and-talk-about-it ethos. We pride ourselves on not having many formal disputes. That’s the last thing we want. We’re here to construct buildings.”

She adds: “Because we are part of the team, we can get in at tender stage and talk about the contract with the trade contractors. That way, there should be no surprises once they have been awarded the job.”

While CWC usually likes to stick to its own contracts, Barclays chose the NEC form for fit-out at One Churchill Place. Wright says: “It was very exciting and different and quite good fun. You have to put in a lot of effort at the beginning in both time and money to make sure it’s managed properly but, once you start going, it works really well.”