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Lighting gantry and bridges to auditorium

working details

The auditorium of the theatre is circular in plan and enclosed, for acoustic isolation, in solid, double-skin blockwork walls.

The plant room above is also isolated by a 100mm 'floating' concrete floor set on resilient bearing strips; these in turn rest on the main roof slab of TermoDeck precast-concrete planks with 50mm structural topping. Fresh air is cooled by being drawn through hollow ducts in the planks; it is then passed via an acoustically isolated duct into a plenum below the auditorium seats.

The complex technical services required by a theatre are organised and accessed by means of a lighting gantry, which runs at high level round the walls of the auditorium, linked by two crescent-shaped lighting bridges that cross it. The gantry gives access to front and rear areas of the auditorium.

The floor of the gantry and each bridge is formed of 100mm concrete, cast in situ between a pair of 260 x 75mm PFCs (parallel flange channels), one at each side. These are bolted to a series of paired 48.3mm-diameter CHS hangers that are suspended from the roof structure. The concrete slab floors present clean, uncluttered soffits to the audience below and a wiremesh balustrade along one side of each bridge screens services. A series of curved acoustic baffle panels are suspended between the bridges to reflect sound into the rear of the auditorium.

The curved blockwork walls are generally finished with a hard render/plaster coat set with U-shaped aluminium angles.

Built as panels to reduce their scale, they also prevent cracking.

In specific areas the walls are recessed and fitted with 25mm maple-veneered MDF acoustic panels, pre-formed to wavelike curves to break up lowfrequency sound waves.

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