High school

Twenty-four storeys up on the south side of London’s Canary Wharf, the views in every direction should be stunning. But there is nothing to see except protective boards, and away from the hustle and bustle of ground-level site activity, it feels strangely quiet and isolated.

For the six joiners and two labourers constructing the building’s concrete core, which involves repeating the same operations week after week as the structure grows, one floor at a time, it’s a distinctly boring situation. ‘It’s like Groundhog Day,’ says site supervisor Colin Judge, who employs humour to keep his team going.

‘The boredom of being behind the screen affects them,’ says Declan Hagan, project manager at J Reddington, which is carrying out the groundworks and concrete frame on The Landmark residential project in the Docklands. ‘When the boys come down from there they say it’s like being in a prison,’ he adds.

This is an unusual project for Reddington. ‘This is one of the highest concrete frames around,’ says Hagan. Commercial towers are often steel frame at this height, but for residential applications such as this concrete frame can be more appropriate due to considerations such as noise and vibration. And concrete frames are bread and butter for Reddington. ‘It’s no different to anywhere else, apart from the height,’ says Hagan.

But there has been one day of excitement for Judge and his team. The core steps in at the 10th floor with the wall thickness shrinking from 450mm to 300mm, because less structural concrete is required due to decreasing load higher up the building.

This presents an interesting problem. Normally, the formwork would need to be dismantled and craned off to move into a new position to accommodate this change in wall thickness. Reddington, however, is using a rail climbing system (RCS) from Peri, which allows it to accommodate small changes in horizontal or vertical alignment, and so can move up continuously. But Peri had only done the operation in Germany before. So there was a certain amount of trepidation the morning the operation took place, especially since John Reddington himself, who founded his company in 1996, was on site to watch the proceedings.

The operation ran smoothly. ‘It went all right,’ says Judge. ‘It was all done without lifting anything off at all.’

The 31-storey West Tower and its 45-storey partner, the East Tower, form the main part of The Landmark, which will become home to City types working at Canary Wharf. The lower floors of both towers and one of two lower-level social housing blocks will also contain restaurants and shops.

Both towers have already been bought from developer and main contractor Chalegrove Properties by Young Group which will sell the 644 flats on. In fact, it says that all 276 flats in the West Tower, which it bought first, have already been reserved.

Reddington is well into its 20-month programme. The groundworks were extensive and encompassed piling, secant walls, capping beams and raft slabs to create the basement for the underground car park as well as the foundations for the buildings. There were some massive pours – up to 200m3 – below the tower blocks.

The cores of both the West and East towers are well on their way to completion, with one of the two smaller blocks just rising out of the ground.

The layout of the apartments, in which some of the bathrooms sit within the core structure, means that the concrete core is huge. ‘It’s the biggest one I’ve ever seen,’ says Paul Gabbitas, Peri’s site demonstrator. And he has seen a few: a joiner by trade, his job is to spend time on site with Peri’s customers getting them going with the equipment. The core layout means that there are plenty of walls to be cast at each level.

Reddington is one of Peri’s biggest customers and, according to Hagan, Peri was a natural choice for this job. ‘We know Peri and we know that they are a quality product and we get the technical back-up from them,’ he says.

It takes two lifts to get into the swing of things. You could not bring five new blokes up and keep going.

Colin Judge, J Reddington

The Peri RCS system is relatively new to the UK and this is the first time that Reddington had used it. Gabbitas spent five weeks on site initially working with Judge and his team to get the system going.

‘It’s just like a big mechano set really,’ says Gabbitas. ‘But it’s not like it used to be when all the kit just arrived on site and you had to work out how it went together. There is a fabrication drawing for each platform, with details down to what nut and what bolt you need. But it is daunting at first because there’s so much stuff.’

The RCS system has three levels of platform, the lower two of which were prefabricated by Peri. The top platform is larger and had to be assembled on site, with Peri providing the components pre-cut.

RCS can be lifted up from pour to pour using a crane, or it can be ‘self-climbing’ using hydraulic rams. On this job, hydraulics made sense. ‘Using the hydraulics means the crane is released for everybody else on the job,’ says Judge. Even so, and even with four tower cranes, craneage remains a challenge on a job like this, according to Hagan.

To the uninitiated, self-climbing formwork might make life sound easy. Once you’ve seen the operation, however, you realise how much work it takes to move from one storey to the next. Judge reckons it takes two lifts for everybody to get to know how the system works. After that each person knows their job for each day of the week.

It’s important to keep the same people for the whole operation: ‘You could not bring five new blokes up and keep going,’ explains Judge. ‘Even with one new person it would take three weeks to get into the swing of things.’

How does Reddington make sure the same joiners stay on the job? Hagan says using people who live locally makes them less likely to move on and points out that the joiners on this operation have been with the firm for a long time. They are also likely to move onto a different sort of job next which will relieve their boredom, he adds.

When Judge and his team started, it took six days to prepare and cast each storey. The concrete would be poured on Friday – 100m3 when the walls were 450mm thick, 59m3 with 300mm walls – the bolts would be removed on Saturday and the system lifted on Monday, taking around six hours using hydraulic jacks to lift up each section in turn. Then the shutters are cleaned, the rebar is fixed and the shutters are aligned in time to to pour again on Friday.

Judge says he can do it in three days now if the steel fixers have had time to prefabricate some of the rebar down below, with an average cycle taking 4.5 days. However, they cannot speed ahead since they must wait for the decks below to catch up. ‘We should be finished by now,’ says Judge.

The clever bit about Peri RCS is the shoes, which attach the climbing formwork scaffold to the side of the core (see diagram attached).

Unlike some rival systems, Peri’s shoes allow flexibility in two dimensions. This has proved useful for two aspects of this job. First, for the change in wall thickness where the system had to be tilted in and slid upwards to achieve the 150mm step in. On the taller tower, there are two smaller steps of 75mm. Having carried out the procedure with Gabbitas’s help on the first tower, Judge was able to show the gang on the second tower how to do it. ‘Peri were on their way to site and we’d already done it,’ says Judge. The vertical rails are also jointed with one pin which assisted the movement.

Second, the shoes have proved useful for attaching the protective panels for the following floors to the ends of the building where precast balconies are attached. The horizontal railings cannot be bolted into these balconies since they cannot hold the weight, so the rails are bolted back to the main structure and cantilevered out at an angle to the horizontal over the balcony to avoid putting weight on them. The shoe at the end of the rail has to pivot slightly so that the vertical screens are vertical.

Despite the waits for the decks to catch up, the cores and the project are on programme. For Judge, those last few lifts cannot come soon enough. ‘This is the first [core] I’ve worked on,’ he says. ‘And I hope it will be my last.'