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Structures: Hospital tower’s lifeline

A competition-winning team has come up with a novel solution for recladding a 1960s hospital on a very congested site - without disrupting operations inside. Margo Cole reports.

Following the triumphant design and build of the 2012 Olympic Games velodrome, the team behind it, which has drawn accolades including ICE London’s team of the year, are no strangers to acclaim.

And so construction firm ISG, architect Hopkins and engineer Arup joined forces once more to scoop another high-profile design competition for a very different public building project on the opposite side of London. This time, the three firms set out to forge an innovative solution to a problem that has plagued St Thomas’ Hospital for many years: a leaking building.

The hospital’s 11-storey East Wing building, which sits across the Thames from the Houses of Parliament, was built in the 1960s and has a T-shaped plan. Its unusual teak, stainless steel and slate façade has never been great at keeping rainwater out - to the extent that it has been covered in scaffolding for over a decade.

Aware of the complexity of carrying out construction work on the congested hospital site, client Guy’s & St Thomas’ NHS Foundation Trust opted for a contractor-led design competition under the auspices of the Royal Institute of British Architects (Riba).

St Thomas' hospital truss

Support: The atrium walls are supported by 30m-long trusses

“We assembled a team of designers that we have a great working relationship with, in the form of Hopkins Architects and Arup,” explains ISG regional engineering director Tim Sullivan.

“Riba had never done a contractor-based competition before, but it was the right way to do it because the client wanted a high-quality design solution - but not a high-quality design solution that couldn’t be built. And they wanted a team approach.”

“Arup spent a long time making sure they were comfortable putting the new loads through the building. We are putting massive stress into the existing concrete frame”

Tim Sullivan, ISG

The client’s brief was deceptively simple: prevent the ingress of water through the existing façade and provide two new bed lifts. However, there were two major constraints; the team had to consider the implications of the location, and also provide a high-quality design solution that could be built within a live hospital environment with the building fully occupied. The trust also gave an indicative price for the work of £27M.

The East Wing houses a range of hospital activities, including wards for heart patients and operating theatres. It sits cheek by jowl with other buildings on a congested site, almost touching the adjacent Evelina London Children’s Hospital built in 2005.

Steelworker at St Thomas' Hospital

New for old: New steelwork is fixed to the existing concrete frame, while the old cladding stays in place

As the tallest building at St Thomas’, it also stands out, looming above the hospital’s low-rise river frontage buildings. It is highly visible from the Houses of Parliament, which put the design team under added pressure to come up with an attractive - as well as practical - solution.

At the heart of the competition-winning entry was the decision not to remove the existing cladding, which the team deemed to be too noisy and disruptive for staff and patients. The designers also felt the existing materials had architectural merit.

“Some of our competitors were trying to get rid of the façade, but our approach was about utilising what we’ve got already,” explains ISG engineering manager Jay Munoz.

Hopkins project architect Thom Kilvert adds: “We asked ourselves can we re-cover what’s there? It’s good quality slate, teak and stainless steel.”

Glass box

The result was, effectively, to enclose the entire building in a glass box. On the river-facing west façade, this takes the form of a glass wall that hangs from the roof, with a gap of 1m from the existing façade. At the back of the building, the new glass walls span diagonally between the corners of the T-shape, creating two large enclosed atriums, each triangular in plan. The atriums begin at second-floor level and continue to the top of the building, where they are topped with ETFE roofs.

“Rather than taking the existing cladding off, we are keeping it on and over-cladding it,” says Sullivan.

“We felt we couldn’t take it off because there are patients in there, so we are making the existing fabric of the building more energy efficient. And at the same time, we are creating diagonal atriums on both sides, which gives [the hospital] new space that they can occupy and use.”

“Some of our competitors were trying to get rid of the façade, but our approach was about utilising what we’ve got already”

Jay Munoz, ISG

The existing cladding system includes a fairly early form of double-glazing that does not perform very well, contributing to solar gain in the summer and heat loss in the winter. “With a new façade we could put in solar control glazing to prevent overheating, as well as natural ventilation on both the west façade and the atrium,” explains Kilvert, adding that the building would no longer cool down as quickly in winter.

The new ETFE atrium roofs are also designed to reduce solar gain, with all the south-facing panels being opaque so that light, but not heat, is let in.

The design addresses the trust’s need for two new bed lifts by incorporating a completely separate lift core on what is currently the external wall of the building. This will ultimately be enclosed inside one of the new atriums. “When it is ready, we will just break into the existing building at each floor level,” explains Sullivan. “So our scheme avoids any real interfaces with the internal workings of the hospital.”

It also gives the trust the flexibility to remodel the interior of the building in future. “They have in mind that they want to refurbish the existing building, so there are a lot of areas where we have created risers with nothing in them, that in future can house new plant and equipment,” says Sullivan.

Collaboration: Getting the green light from the trust

St Thomas' Hospital

From the air: The central London site is very constrained

In opting for a contractor-led competition for the East Wing external refurbishment, Guy’s and St Thomas’ NHS Foundation Trust sent out an important signal as to what it was looking for.

The trust wanted a team whose members were already comfortable with each other, with buildability high on its list of priorities. The trust also made it clear that it would work closely with the winning team to make sure day-to-day disruption of the hospital’s working was minimised.

“This is a critical building for us. It houses cardiac theatres, in-patients and high dependency units, so any disruption is going to be a major problem if it impacts on our ability to operate,” says the trust’s programme manager Chris Moriarty-Baker. “We need to minimise any disruption as much as we possibly can.”

Before work could begin, the design and build team and the trust’s project board agreed a brief that stated how key aspects of the project would be dealt with such as working adjacent to areas where radiation is present in hospital equipment, and liaising with staff and patients. They also agreed key times during the day when the team could not make any noise that might be heard inside the tower.

“We held a ‘noise day’, when we made lots of noise-simulating construction activities - like skip lorries coming in and bringing in scaffolding,” explains ISG regional engineering director Tim Sullivan.

“Trust staff stood in lots of places with noise monitors and told us what was acceptable.”

As a result, the site team came up with some alternative methods such as using diamond drilling to cut into the tower’s concrete frame, rather than percussion drilling.

The design and build team and the trust also developed a ‘traffic light’ system for potentially disruptive activities.

“Anything that we know is going to be disruptive is red, and we have to have a dummy run beforehand so everyone knows exactly how it’s going to work,” explains Sullivan.

“Amber activities have to be done at set times, and green can be done at any time.

“At end of the pre-construction phase, in tandem with the trust, we had de-risked the job for the client, and they knew what the risks were in advance,” he adds.

 

Due to the site’s congestion, inevitably the space alongside the East Wing that will now be within the footprint of the new atriums was being used for storage and plant. Some of this has been relocated elsewhere on the site, including within a new plant room that ISG has built on the roof of the tower. However, there was not much room for manoeuvre on major installations, including a substation and three oil tanks holding a total of 150,000l of oil.

This is why the atriums begin at second floor level, and cantilever out over the large plant items. These have been moved slightly to enable segmental flight auger (SFA) piles to be installed, and a new tank built outside the footprint. The piles support columns that will carry the loads from the cantilevered atriums, including Y-shaped columns beneath the long edge of the atrium floor.

St Thomas' hospital

Façade: Glazing hangs from roof-level steelwork

The new floor itself is made from reinforced concrete, infilled with glass blocks.

“The piling was very close to some of the existing plant,” says Sullivan, explaining that ISG had to expose the tower’s existing piles and pile caps to confirm that both their size and location were suitable for the new loads that will be added to the structure from the cladding and atrium floors.

“Arup spent a long time making sure they were comfortable putting the new loads through the building,” he adds. “We are putting massive stress into the existing concrete frame.” These stresses include a 1.2MN load at the corner of the cantilever floor.

“To get to the stage where we could start to construct was a whole exercise in itself”

Fraser Tanner, ISG

The glass atrium façades are supported by 30m long steel trusses positioned diagonally between the wings of the building at alternate floor levels. Each truss is delivered in three 10m sections. The sections are then welded together on site, and the completed truss is lifted onto three scaffold towers, then welded to plates fixed to the existing building.

“There is quite a lot of steel, but it is quite an efficient design,” says Kilvert. “There are only five columns.”

A basement beneath the west façade made it impossible to build foundations for the new glass wall on that side - hence the decision to hang it from new roof-level steelwork. This new steelwork will form the roof of an extra storey that ISG is adding on this section of the tower, replacing temporary accommodation the trust had been using as offices for many years. The façade itself was erected using mast climbers.

Once piling for the atrium foundations was complete, ISG built what it calls a ‘dance floor’ - a platform at second-floor level, from which it has been carrying out all the construction activities for the atriums.

“We needed to be up on the second floor, so we put up flights of scaffolding and put a platform all round,” says ISG senior project manager Fraser Tanner.

The dance floor also gave the contractor somewhere to store materials - something that would have been impossible at ground level with space in such short supply.

“To get to the stage where we could start to construct was a whole exercise in itself, but we always knew that the only way we were going to manage this job was to get it up to second floor and create a designated area to work from,” says Tanner, who explains that a total of 50t of scaffolding - made up of 30km of tube and 26,000 fittings - has gone into the temporary works.

The congested site also means there is only enough space for one tower crane - a 500t crane with a 60m jib that was erected this time last year - over the May bank holiday weekend. This involved building a base that had to span some existing structures, resulting in very high eccentric loads. Of the 34 SFA piles installed, four were for the tower crane base.

In the subsequent 12 months, that crane has been put to good use, with the new west façade now complete and the new atriums and lift core well under way. The work is scheduled to take a total of 78 weeks, and should be finished in the autumn.

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