Contractors have raised the roof on the redevelopment of an historic Victorian building at Nottingham Trent University
Main contractor:Bowmer and Kirkland
Brickwork contractor:Irvine Whitlock
Consulting engineer (temporary works):Smart Crosby
Temporary works supplier:Mabey Hire
Temporary works erector:Ashfield Scaffolding
Piling subcontractor:Roger Bullivant
It is often wrongly assumed that you cannot make any alterations to a listed building without incurring the wrath of government watchdog English Heritage.
But while there are undoubtedly some fanatics within the wider heritage movement, the legislation protecting our historic buildings is pragmatic in its approach. There has to be a balance between preserving the essential fabric of a building and allowing the building to adapt to current needs.
Having said that, the degree to which the chemistry block at Nottingham Trent University’s Arkwright Building is being adapted is pretty extreme for a Grade II* listed structure.
The Arkwright Building is a city landmark, built for University College Nottingham in the late 1870s. Its historical significance extends beyond its Victorian gothic architecture. It was here in the chemistry block in 1904 that Professor Frederick Stanley Kipping discovered silicone polymers and laid the foundations for what is today a multibillion-dollar industry.
Now the Arkwright Building is at the centre of a £70 million redevelopment. The project will involve the extensive demolition of part of the site and the construction of a large glazedroof atrium linking the chemistry block to the nearby Newton Building - a Grade II* Modernist building designed by Cecil Howitt in 1952.
Most of the chemistry block’s architectural merit centres on its roof, which features ornate timber trusses and beams. But because the block was built as an integral part of the Arkwright
Building, its walls were all effectively internal structures.
Only the upper section of one gable-end featured external brickwork and the block’s only windows: three tall casements with gothic arches. Most of the daylight entering the block came from roof-lights running the length of the building on either side of the ridge.
Removing the walls Demolition of the surrounding structure not only exposed these internal walls but removed much of what supported the block. The redevelopment, designed by Hopkins Architects, therefore proposed new external walls, using methods and materials in the style of the Victorian architecture, to create a new standalone building.
In order to replace the walls while retaining the roof, a temporary method of support had to be found. The subcontractor responsible for this, brickwork specialist Irvine Whitlock, had
already noted the use of temporary plan-propping on the nearby Newton Building and approached
supplier Mabey Hire in search of a solution.
Mabey’s suggestion was a temporary structure assembled from its modular System 160 ‘soldiers’. These heavyduty steel props are supplied in a range of eight lengths from 360 mm to 4.5 m. They come with a range of accessories, including threaded end-attachments for fine adjustment. These props would be used to support the roof while Irvine Whitlock demolished the wall below and built up the new brickwork.
A logical sequence would have been to tackle each elevation individually, propping only those areas of roof temporarily without supporting brickwork.
However, below-ground investigations soon ruled this out. “We discovered the whole building was erected on very poor ground, including a lot of old fill,” says main contractor Bowmer and Kirkland’s project manager, Darren Lomas. “And when we did an excavation in one corner of the building, we discovered there were no proper foundations, so we had to underpin the building with a concrete ground beam to support the new walls.”
To demolish and rebuild each of the four walls would therefore have involved both Mabey and foundations contractor Roger Bullivant paying numerous visits to the site. But it made better sense to prop the whole building at the outset, allowing demolition to proceed to suit the programme. Then the minipiles and concrete ground beam could be installed before starting on the new brickwork.
Mabey’s method involved propping the eight purlins and the ridge beam at the east gable so that this gable could be removed and replaced. The six timber roof trusses were supported along the north and south elevations, so the whole of the north and part of the south elevation could be removed and replaced.
The upper half of the west gable, containing the three gothic windows, was supported by passing six System 160 needle beams horizontally through holes made 4.5 m up the wall.
The loads from the needle beams were then transferred to vertical 160 soldiers inside and outside the building. These were adjusted to accommodate the load and, with the upper half of the wall thus supported, the ground floor wall was ready to be demolished.
All the Mabey props were supported on the ground by the existing concrete floor slab, augmented with sections of concrete beam where necessary.
With the exception of the needling supports at the west gable, all the temporary supports were located within the building envelope, leaving plenty of space for Irvine Whitlock to erect the new walls.
“None of the temporary works interfered with the brickwork,” says Kevin Pedley, site manager for Irvine Whitlock. “It did create some issues with our scaffolding, which had to be built around the Mabey props.”
The rigidity of the supporting structure was a big consideration, says Mabey Hire’s area sales manager, Mark Gent. “Although the loads involved are not great, the height of the building posed difficulties,” he says. “The height to the roof trusses is about 5.4 m and the height to the roof ridge is about 10.2 m. We had to design a system that would prop five large roof trusses and nine purlins at one gable-end.”
Mabey used 10 pairs of System 160 props to support the roof trusses at 5.4 m height, bracing them with additional raking props at about 45 degrees. These were anchored to a concrete beam cast down the centre-line of the building.
Propping to the eight purlins and the ridge-beam required individual props of between 7.3 m and 10.2 m high. Horizontal bracing was provided by tying adjacent props together with scaffolding tubes and clamps.
“The fact that all the propping had to be internal meant that the System 160’s ease of manual handling helped in the erection of the equipment,” says Mr Gent.
Although strong, the System 160 is light and all components are easily handled by two people.
Installation of the supporting structure was carried out by a local firm, Ashfield Scaffolding of Sutton-in-Ashfield. The loadings were not high.
“The highest loading was on the needle beams in the west gable, where they reached about 68 kN” says Mabey design engineer Steven Dewse.
“On the longest props supporting the trusses, the loads reached 45 kN and on the apex beam supporting the ridge at 10 m, the load was only 7 kN.”
Since the maximum rated capacity of the System 160 props is 200 kN, static load was low on this project.
Stiffness of structure
On the other hand, the stiffness of the structure was a major performance criterion. Irvine Whitlock was required to build up its brickwork to meet the wall-plate suspended above, so movement had to be kept within strict tolerances.
“We plumbed down from the wall plate and then built up to meet that level to within 5 mm,” says Mr Pedley. To ensure this happened, consulting engineer Smart Crosby International required any deflection in Mabey’s temporary supports be kept to plus or minus 3 mm.
A further complication was that there were at least three different ground levels inside the building - largely because Bowmer and Kirkland needed to reduce levels to firm ground and provide a solid base for the Mabey props.
When completed, the building will have a new concrete floor about 500 mm above the level of the original slab.
From erection of the temporary props to the completion of the new brickwork took just four months, commencing in August 2008 and finishing at the end of January. Now, Bowmer and Kirkland is continuing with the wider project to link the Arkwright and Newton buildings.
The project is scheduled for completion in early 2010.
Old and new
Hopkins Architects’ vision for Nottingham Trent University’s redeveloped Arkwright and
Newton buildings uses the residual space between the two buildings to create a new main entrance from Goldsmith Street. This then opens onto a covered central court and link building.
Redundant engineering workshops occupying the lower two levels of the Newton building are to be replaced by a suite of lecture theatres and teaching rooms. They will define a large
central forum designed to promote informal social and academic interaction.
The Victorian Arkwright Building is to be reborn as a centre for university administration.