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Art under attack

Marine Turner Gallery

Margate's new gallery is an exercise in extreme marine engineering, discovers Ruby Kitching.

Why build an art gallery beside the sea when it would be much more exciting to build it in the sea?

It is a question that would leave most engineers gaping in disbelief: Who would design a structure that must withstand the pounding of ocean waves and requires contractors to grapple with winter storms when museums are conventionally built safe and sound on dry land?

But client for Kent seaside town Margate's new Turner Centre gallery, Thanet District Council and Kent County Council, was clearly undaunted when it selected a design by architect Snohetta & Spence following a competition in 2001.

Beached seaward of Margate harbour's stone breakwater, the gallery will face the fury of waves from the North Sea and Thames estuary, with breakers up to 14m sweeping to almost half its height.

The £12.6M visual arts centre takes its name from 19th century artist JMW Turner who went to school in Margate and continued to visit the town throughout his life. The decision to expose the gallery to nature in the raw was inspired by the drama of Turner's paintings, says Snohetta & Spence project architect Stephen Spence.

'We wanted the building to experience the elements.'

Now it is down to engineers to make the project a reality.

Consultant Whitby Bird is beavering away on the Centre's structural design with Arup providing support on marine engineering. To help them understand how the structure will behave in its hostile environment, physical modelling is now under way at test house HR Wallingford.

The Turner Centre is composed of three distinct parts. The submarine conningtower shaped gallery building will house three floors of art above a basement-level plant room. The structure's soaring vault will stand 37m above ordnance datum. Galleries will be linked to the shore by a double deck bridge, with restaurant in a building on the breakwater.

The current plan is to build the gallery shell and floors in reinforced concrete, which can easily provide the required robustness. Its acoustic performance is also attractive.

But a steel frame option is also being considered, drawing on shipbuilding techniques.

'Steel is a more ductile material and can absorb impact loads better than concrete. The structure can be allowed to give a little but still stays intact, ' says Whitby Bird structural engineer Steve Melville.

However, 'the primary concern is to anchor the building', he continues. 'We're currently thinking about reinforced concrete piles 15m to 20m deep embedded in chalk [underlying the sea bed].

Shear walls around the lift cores at either end of the building will stop it overturning from wave loads.'

The basement of the gallery building will contain seawater storage tanks, ballasting the building and aiding stability.

Building services engineer BDSP plans to use this seawater to cool the building.

HR Wallingford's 1:40 scale model is being used to investigate wave overtopping of the gallery and breakwater and to check the potential for scour and deposition. Critically, it will also help the engineers to determine wave loads on the building. The combined effect of offshore wave conditions, the complex shape of the building and the profile of the seabed cannot be analysed sufficiently using normal hydraulic engineering equations or computer modelling.

'Most marine structures are designed for a return period of a 1 in 50 or 1 in 100 year storm. But because the Turner Centre is housing irreplaceable art and being visited by the public, it is being designed to withstand a 1 in 10,000 year storm, ' says HR Wallingford project director William Allsop.

Tests take into account sea level rise due to climate change over the building's 60 year design life.

'In fact if you see a storm coming, you'd be better off heading for this building than any other in Margate, ' quips Allsop.

At HR Wallingford the seabed and coastline have been recreated in concrete in a 35m by 25m tank with waves generated by a bank of paddles. The breakwater is modelled in timber and cement mortar with the gallery carved out of high-density foam and bolted to the basin floor.

Scour and migration of sand and sediment over the chalk sea bed at Margate is being simulated using anthracite, which has a specific gravity suited to the scale model.

Wave overtopping is measured on the model by collecting water in tanks incorporated behind the pier and in the gallery roof where skylights will be located. The architect is keen to have as much glazing as possible, but locations will have to be chosen carefully to ensure it is not subject to the highest wave loads.

'For the 1 in 10,000 year storm, water splashes the top of the building but we expect blocks of waves to rise to 14m above ordnance datum, ' says Allsop. Loads up to 100 times greater than ordinary wind loading are anticipated on the seaward face, he cautions.

Tests have revealed that short duration, high intensity loads will develop as waves travel around the gallery and into the channel created between it and the breakwater.

A groyne may be necessary to prevent scour. And close attention will have to be paid to glazing and connections on the bridge as waves will swell up underneath it with immense force.

'Loads on the underside are almost explosive, ' says Whitby Bird project engineer Nina Hazell.

Prefabrication plan

The real drama is not the design but 'how you construct this building and how it copes during its lifetime', says Whitby Bird structural engineer Steve Melville.

'We're looking at ways of prefabricating parts to speed up the construction process, ' he says.

One proposal is to fabricate elements in the winter and build in the summer months when conditions are more favourable.

Prefabrication is also favoured for reasons of weight and manoeuvrability. There are doubts as to whether the breakwater is strong enough to cope with fully laden concrete trucks, while assembling ready made components offers advantages on a site with such restricted access.

Construction is expected to get under way later this year for completion in 2006-07.

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