Well, one of them is an access platform that keeps steelworkers safe and another is a steel contraption that halves the time taken to raise tower cranes. And these are just a few of the innovations helping CWC to build smarter
If practice makes perfect, Canary Wharf Contractors must be getting close to perfecting the art and science of high-rise construction. Since the start
of the second phase of development at Canary Wharf in late 1996, it has erected six high-rise buildings, more than any other UK-based contractor.
This experience comes across in the attention lavished on seemingly inconsequential details such as the carbon and silicon contents of the structural steelwork. Charlie Paul, CWC’s structural construction manager, explains: “We check the carbon content so we don’t have to preheat the steel prior to site welding. We will also talk to Corus about the silicon content if we have to galvanise the steel.”
Paul had more than 30 years’ experience of steelwork contracting before joining CWC in 1999. Like most of its staff, he was hired for his specialist knowledge.
At Canary Wharf, says Paul, “you could make an early policy on how to construct the building from the conceptual design. If the architect and designers haven’t got it quite right as far as building it is concerned, you have an opportunity to change that.”
Senior construction manager Richard Lines adds: “On day one, the team gets together to start talking about what it’s all about and the details come out of that.”
From these discussions come ideas on which method of construction best suits the building, where to locate the cores and plant rooms, and where to site the tower cranes (see plan, right).
Don’t fence us in
On day one, the team gets together to talk about what it's all about. the details come out of that
Paul notes: “We may ask the designers to change some details so it gives us the option at tender stage to go for a slip-form or jump-form for the concrete cores.”
Lines says it is critical not to tie concrete contractors down to either method. “To get the economic benefits, you have to have a market where trade contractors will come forward and give their options.”
A huge amount of time is spent developing ideas: 19 crane layouts were contemplated for One Churchill Place, with detailed drawings indicating the operational capability of each crane and the designated positions for vehicles delivering materials. An internal review of the 19 schemes ended with seven options being made available to bidders.
Paul comments: “It meant contractor A could say my price is based on crane scheme X, while contractor B could say mine’s based on scheme Y. Nobody was disadvantaged and it was all about selecting the bidder based on programme, technique and money.”
He reckons solving the crane conundrum, which involved relocating cranes on top of the cores once slip-forming had finished, probably saved about £1m.
If the 210 m high cranes had been located elsewhere, the foundation works needed to support them would have been hugely expensive.
Paul adds: “To climb a crane externally from the lowest to highest levels would have cost £100,000. With five cranes that’s £500,000. So once you’ve added money spent putting the foundations in and taking them out, we must be talking about £1m.”
A couple of years earlier, while constructing 10 Upper Bank Street for law firm Clifford Chance, CWC came up with a novel tool to cut the time taken (sometimes up to four days) to raise tower cranes that were sited inside the building cores.
We’ve worked with the best trade contractors and pinched every idea they’ve got, added our own and developed it so we’ve overtaken the industry
The solution was the “Starship Enterprise” – so named because it consisted of two long steel beams at one end and counterweights at the other that looked similar to the spacecraft in Star Trek.
A crane would lift and position the Enterprise within its own mast. Next, beams were added to the two protruding legs to create a jacking platform off which the crane could be raised 30 m. This more than halved lifting time. Lines says: “We have only used the method once, but it is stored in our minds so we can use it again if it suits a particular building.”
Lightening the load
The attention to detail also goes into making sure the steelwork components in the structural design aren’t too heavy for the cranes. Paul says: “We have found instances where the cranes couldn’t do it. So we introduce a splice. For example, the column base plates on Barclays were 150 mm thick solid steel billet and 2 m square.
“Therefore, we put the base plate in, placed the column on top and welded the two together. That had already been decided before we went to the steel contractor. The average construction manager would not have gone into that level of detail and would have relied on the steelwork contractor to tell him that.”
For each works package, CWC’s specialists will examine every detail of the tender. Paul explains: “You can’t expect the surveyor preparing the tender to know about things such as the carbon content of steel.”
At the end of each project, all the parties involved are invited to comment on the lessons learned. A file nearly 25 mm thick was accumulated just for the steelwork package on One Churchill Place. Similar appraisals were undertaken for all the other trades.
Paul says: “We have worked with the best trade contractors and pinched every idea they’ve got, added our own and developed it to a stage where we’ve overtaken the industry.
“They still have unique products to offer us, but we hone them down to exactly what we want and what we need.”
Protecting the men of steel
Forget the famous 1930s image of steel erectors sitting on a beam hundreds of feet above the streets of New York. Time and health and safety legislation have moved on.
Steel construction remains a risky occupation but, at One Churchill Place, CWC decided it didn’t want to see any workers balancing on beams. Charlie Paul recalls: “When we said ‘no men on steelwork’, many in the industry said it couldn’t be done. The Health and Safety Executive wanted us to use safety nets, but we felt that had its own set of risks – we wanted something better than that. And the proof of the pudding is we did it.”
CWC asked steel contractors to come up with the safest solution. Paul says: “We had complaints from tenderers, saying that if they put in the best safety system, they would not win the job because others would adopt a cheaper solution.” This issue was resolved by getting the contractors to price the job and put in a separate sum to develop the safest system.
Victor Buyck-Hollandia, the Belgian-Dutch joint venture, won the steel package on the strength of its idea to use “cherry-picker” access platforms.
Each cherry-picker was mounted in a special assembly, which allowed the machine to travel backwards or forwards a few metres, enabling the erectors to manoeuvre the passenger cradle right next to where the steelwork had to be bolted together. After each operation, the unit was lifted by tower crane and repositioned.
As the decision to use cherry-pickers was made during the conceptual stage, there was time to change the design of the beams so they were strong enough to support the 7-tonne units.
Paul says: “It didn’t cost much, if anything.”
Another innovation at One Churchill Place was the development of a safety clamp that could be affixed to beams above an erector’s head. The clamp has small wheels that allow it to travel along the length of a beam and is attached via a fall arrestor to an erector’s safety harness.
WHARFpeople - Iggy Parry
Iggy Parry started work at Canary Wharf in 1996 when 33 Canada Square was getting under way. This was a landmark scheme by Foster and Partners and the first to be built east of the iconic tower at One Canada Square.
Since that project, Parry has taken on the role of senior planning manager at the wharf, setting up strategic plans for most of the buildings subsequently completed on Bank Street and Canada Square.
“We are unique in being able to offer some of the shortest times from sign-up to move in,” says Parry. “We also incorporate our tenants’ specific engineering requirements in the design of the building.”
Typically, large banks require enhanced electrical systems for resilience as well as dual cooling systems to ensure IT centres remain online at all times.
“While our buildings are unashamedly the best in contemporary architecture, they are essentially large machines that not only accommodate people, but also house the incredibly complex electrical and mechanical systems that are the heart and arteries of the building,” he adds.
Parry has been involved in several studies of the various construction techniques undertaken at Canary Wharf. “We looked at different ways of forming the concrete cores that are incorporated in all the wharf’s tall buildings, comparing slip-form and jump-form techniques. We have used both successfully and both have merits. We have also looked at the most economical and time-effective ways of constructing basements, balancing the early start of concrete work and the lead time of structural steel.”
However, the nuts and bolts of the job is taking a systematic approach to planning and monitoring large schemes. Parry has a team of project-based planners who manage the day-to-day work. “We start with the project’s delivery objectives and work down to detail the design, procurement and construction programmes. There’s no substitute for attention to detail, close monitoring of our trade contractors’ planning, spotting when something is going astray and doing something about it.”
He adds: “Planning tall buildings is fascinating, especially when you are aiming to improve on the achievements of the last one. We have built six towers over 30 storeys in the last seven years and each time, we get more efficient as systems are refined.”
Bring on the next one.