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Wave of applause

Technical feature Sage music centre

The eye-catching roof of a music centre is helping to transform the River Tyne's once derelict Gateshead quayside into the 'South Bank of the North'. David Hayward reports.

Construction of a vast steel wave, about to break and tumble downward into an adjacent river, is now under way on the banks of the Tyne at Gateshead.

Such a flowery description for what is, in reality, just the profiled roof of a new concert hall warrants no apology, for two reasons. The architect is Norman Foster, and the £70M music centre - one of the most acoustically advanced anywhere - is destined to become the focal point of Gateshead's impressive cultural redevelopment of its once derelict quayside.

The city that offered the construction industry such inspiring successes as the tilting Millennium footbridge, just downriver, and the nearby Angel of the North sculpture, completes the trio with a Sydney Opera House style structure billed as equally challenging to designer, builder and end user.

'It certainly ranks among the most complex roofs we have yet designed and erected, ' claims Martin Wallbank, project manager for Austrian steelwork specialist Waagner Biro, contractor for the £8M roof structure's detailed design, manufacture and erection. 'None of its 3,000 plus steel frame sections is exactly the same shape and the multi-curved geometry offers dozens of different radii.'

The music centre - recently renamed The Sage after its locally based principal sponsor, software manufacturer the Sage Group - offers state of the art briefs for both structural design and internal use.

Three structurally and acoustically separate music halls will host performances ranging from full orchestral concerts to jazz, folk sessions or piano solos. Beneath the main auditoria, two dozen soundproofed smaller rooms offer training, rehearsal, educational and recording studios.

Yet to most visitors it will be the building itself that offers the initial 'wow' factor. Enveloping the three halls, but structurally separate, will be 1,000t of curved, partially glazed silver steel roof resembling a large cascading wave.

With near half the 100m wide roof's undulating steel beam frame now bolted into position, the dramatic end profile can be seen. But already the inevitable learning curve for such a oneoff roof design has altered the planned erection method.

The frame is founded on four long primary ribs, formed of universal beams and curved tightly over the building. The ends of each 140m long rib are tied between rear concrete abutments and the top of a deep retaining wall forming the building's steep riverbank frontage.

Each primary rib, formed of 11 bolted sections, is supported by a row of four, up to 28m high tubular steel columns. These are raked at differing angles and rise from the ground level slab between - and independent of - the three main halls. Secondary and tertiary roof steel spans transversely between the ribs.

Given this multiplicity of odd shapes and sizes, Waagner Biro had originally hoped to erect much of the frame from large preassembled sections. These were to be bolted together at ground level from an average 35 individual units, and raised as one 6t lift.

'But with a single hook lift, the awkward shaped assembly proved difficult to align in the air and bolt on to neighbouring sections, ' Wallbank recalls.

'The operation proved very labour intensive, so we have resorted to conventional piecemeal erection.'

But this actually reduced all important hook time, as two of the site's three tower cranes had been needed for the preassembly operation. One serviced the bolting of sections on the ground and a second, with longer reach, carried out the main lift.

Piecemeal erection improved productivity by 50%, claims Wallbank, and eased the structural challenge of ensuring sections were not overstressed during lifts.

The frame's design, with its network of struts and ties, ensures that both dead and live loading - even during erection - leaves it lightly stressed. The total roof weight is transferred to its 27 support columns, each piled up to 16m deep into underlying rock.

Cladding the roof frame starts next month, with the primary 100mm thick galvanised metal decking, and composite 60mm insulation layer, bolted tight to the frame to act as a waterproofing membrane. The outer cladding of 2,500 flat silvery steel panels will start next March.

This 10,000m 2covering, with glazed side and front sections, will stand 650mm proud of the metal decking. Its role is largely cosmetic and, with flatness tolerances of just 5mm between 4m long panels, smoothness is an architectural necessity.

Small screw jacks, fitted at panel joints to help ensure accurate alignment, were one of the value engineering advantages to emerge from an unusually long preconstruction period. Main contractor Laing-O'Rourke won the £50M construction contract back in December 1999, but it was spring 2001 before site work started.

'We brought the winning company in early to inject a contractor's buildability skills into the design team, ' recalls Peter Udall, major projects manager for client Gateshead Council.

'This led to us minimising construction interfaces by offering the roof as a single contract, instead of the four separate packages originally discussed.'

Beneath the roof, what look like three large concrete boxes are, in reality, state of the art music centres boasting an acoustic design that can be fine tuned to enhance the precise sounds on offer.

The boxes house a multitiered concert auditorium, a smaller 10 sided less formal hall and, between them, a large rehearsal centre. All three could be in full musical flow without either neighbouring halls, or the thousands of visitors in surrounding open concourses, knowing anything about it.

Consultant Arup Acoustics had even to allow for the noise of a helicopter on a nearby helipad arriving at the heart of an orchestral symphony's slowest movement.

The solution is a physical 50mm wide 'acoustic gap' cut into floor slabs surrounding each hall and designed to reduce structure borne noise. This total 800m long 'cut' is routed round the halls on all five slab levels, vertically dividing walls, columns and concrete floors to acoustically isolate all three auditoria from each other.

Additionally, each hall has a secondary outer blockwork wall, with the 150mm gap to the structural wall acoustically padded to help muffle airborne noise. Practice rooms on lower levels are similarly double walled, with the noisiest of them boasting raised internal floors supported on neoprene rubber bearings, and ceilings hung on springs.

Noisy air conditioning is out; replaced by an innovative network of padded ducts feeding a low pressure air supply direct to the bases of all 2,000 audience seats. Here the forced air passes up each individual cylindrical seat stem and diffuses out through holes in it to 'ventilate' the occupants at close quarters.

But the real clever bit, says Arup Acoustics associate Ian Knowles, is the way the hall's internal fittings can be adjusted to suit each performance and the numbers attending it.

'Fabric banners on the walls, and deflectors in the roof space, can be raised or lowered to create the exact acoustic absorption factors for the type of music being played, ' he explains. 'We can even adapt these acoustics to allow for different sized audiences.'

But such sophistication will be overshadowed by the roof shape which, from early next year, will start to dominate the structure. Opening is planned for summer 2004 and, to demonstrate its versatility, the music centre is already booked for the spring 2005 Labour Party Conference.

Project team

Client: Gateshead Metropolitan Borough Council

Architect: Foster & Partners

Roof consultant: Buro Happold

Substructure consultant: Mott MacDonald

Main contractor: Laing O'Rourke

Detailed roof design, manufacture and erection: Waagner Biro

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