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Hi-tech court house framed up

SITE REPORT

The skin of Manchester's new Civil Justice Centre is mostly glazed, a design intended to reflect the transparency of the judicial system. But supporting the glass is a steely heart ? another aspect of the courts that some plaintiffs may recognise. Bovis Lend Lease is building the unusual addition to the city's skyline. Joanna Booth heard the evidence

WITH ITS dark central spine, a glazed atrium to one side and unevenly stacked floors to the other, from some angles the Manchester Civil Justice Centre bears a passing resemblance to a pile of books.

But the 16 -storey, 85m-high building will house a lot more than the weighty tomes of law. Inside the vast structure there will be 47 courts, each with its separate retiring suite for a judge, plus consultation rooms which hang at random points up the walls of the 65 m-high atrium, formed by the highest hung glazed wall in Europe.

Supporting the atrium's glass wall are triangular steel columns. Three slip-formed concrete cores ? one the size of a tennis court ? are spaced along a central spine section. A steel frame building with concrete decks, it is clad in a traditional panel and stick system. To the other side of this rise the most visually surprising elements of the building ? an asymmetric pile of glazed fingers jutting in and out over one another. Each finger comprises a single or double-storey box formed from steel elements with thick glass walls, and together they house the courtrooms themselves. A coloured internal panel system will be easily visible from outside, in the signature yellow of Australian architectural practice Denton Corker Marshall.

Bovis Lend Lease won the £113 million design and build package and started on site in spring 2004 with complex enabling works, including a secant piled wall.

'We also took the opportunity to put a permanent service road in prior to main contract works starting, ' explains Bovis project manager Peter Foy.

Currently just past the half-way point, the job is on programme and scheduled to finish in January 2007.

The complex sequencing of the project had been agreed with engineers Connell Mott MacDonald. The three cores were slip-formed at a rate of around 3 m a day and then the central box building completed around them, where concreting and early fit-out could begin.

The biggest technical challenges on the project came from the steel ? both in the construction of the fingers and the steel columns supporting the atrium.

To meet these Bovis went to the steel market early to investigate the technical options open to them prior to formal tender. After discussions with a number of the major suppliers, traditional competitive tender led to the early appointment of William Hare in April in 2004. The steel firm had a comfortable lead-in time of nearly 30 weeks and is contracted to provide 3,000 tonnes of steel to the project.

Once the main box was well under way the fingers were next to start const ruct ion and proved one of the biggest challenges on a complex project.

With extremely high tolerances required, bolting the steel elements together on site was ruled out.

'Because of the complex three-dimensional junctions the elements were manufactured off-site and sectioned for delivery, ' explains Mr Foy. Section sizes depend on what the cranes can lift, but all pieces have to be self-supporting until the box is complete.

Each box is designed as a steel truss, with the high tension and compression forces taken back to the cores through the steelwork itself and also through tension reinforcement. T32 bars are being cast along the full length of each finger's concrete slab, coupled together to form a posttensioned system. Macalloy bars are also used to transfer tension loads through the core walls.

The initial design from the engineers specified back to back beams supporting the main box building where the finger steels connected. But, working with William Hare, the team was able to design a connection detail that allowed a single column, saving on programme and cost.

The fingers were pre-cambered to allow for concreting and the dead load of the façade. The steel went in from the bottom up, but most of the concreting was done from the top down.

Mr Foy says: 'Specific areas and levels were cast and props added to allow further steel to be erected before entire slabs were poured.' The fingers are glazed with a double cavity façade, with a 1 m gap in between the skins allowing the glass to be cleaned. The entire inner skin goes up first to give water-integrity. The outer skin will be installed from the top down. The glazing installers will access the fingers from 22 mast climbers, which tie back into the building. The configuration of these has proven tricky, with the end walls jutting out to irregular lengths above one another. Each mast climber can securely cantilever up to 8 m upwards from a tie.

Hollow triangular steel columns rise 60 m-high along the wall of the atrium at the western end of the building. Exposed and requiring a perfect finish, these presented the team with another brain-teaser. They are fabricated from steel plates, which range from a thickness of 35 mm at the base to 15 mm at the top.

'Initially the architect wanted the plates to be welded together to form a f ine point at each corner but this was difficult to keep constant, ' explains Mr Foy. 'We ended up grinding it flat to get a bit of a lip. But the other difficult is getting a consistent size of weld. When you put two 35 mm plates together there is a bigger gap at each corner than when you put two 15 mm plates together.' Corus, working with engineers from William Hare, set up a special planer so that 20 m lengths of plate could be ground down. This allowed Bovis to achieve a uniform lip size at every corner.

A large truss runs across the top of the atrium at a height of 60 m, with the glass fixed to tensioned wires running down to ties at the ground floor.

Permanent stability and restraint within the atrium is provided by cantilever steel members taking the load back to concourses and core walls.

Room pods will be supported off the beams, scattered in a random configuration up the atrium wall. These will be used as consultation rooms where advocates can meet clients. The building houses 10 lifts for both passenger and goods.

'There's a special secure lift for the judges which lets them out at the back of house in case one of their decisions hasn't been popular, ' Mr Foy says.

For more serious forms of attack, the building has been designed to remain standing even in the event of catastrophic failure.

Mr Foy explains: 'If any one element is removed it will move about, but it will stay up.' The building promises to be a recognisable addition to the city's increasingly high-rise skyline for a long time to come. It is already highly visible, and not just from within the city itself.

'From Bolton, 20 miles away, ' Mr Foy says, 'you can immediately pick out the Beetham tower, the Arndale tower, and us.'

Going with the flow THE CLIENT was keen to minimise energy consumption in the finished building, and lighting and ventilation systems have been designed with this in mind.

Sunlight has many entry points into the building, both through the huge atrium and into the courtrooms through the glass walls.

Natural ventilation is used as far as possible. There is a system for getting air f lowing throughout the building which, according to Peter Foy (right), is 'put simply, a bit like opening your front and back windows at the same time.' On the western elevation ? in the correct direction for Manchester's prevailing winds ? are two wind scoops and sets of louvres.

These are set at a low level on either side of the atrium, allowing fresh air into a duct which acts as a plenum, moving air into the courtrooms. On its way it must pass through baff les made of wire and gauze, to reduce the noise t ransfer.

'The air circulates because of the stack effect, ' Mr Foy explains. 'As the air comes into the building it heats up and rises, finally leaving through more louvres at high level.' If the wind is blowing too strongly, or not strongly enough, the system automatically switches to a mechanised system. 'There are wide parameters of wind speed that it works between, ' says Mr Foy.

The building makes use of the chill waters of the Manchester aquifer for cooling systems. Two 100 m-deep boreholes were drilled during piling works at the north end of the building, and a 60 m monitoring hole at the south end. Water from the aquifer is pumped into the building and used as a coolant in the building's services. 'We could use water out of the tap at 12 deg C or out of the ground at 6, ' he explains.

Project information Design and build contract cost: £113 million Client: Allied London Properties End user: Department of Constitutional Affairs A rchitect: Denton Corker Marshall Principal contractor: Bovis Lend Lease Structural engineer: Connell Mott MacDonald Steelwork contractor: William Hare