The £16 million project included the reopening and re-branding of the City Halls and the old Fruitmarket, two historic live music venues dating back to the 1840s at the epicentre of Glasgow's Merchant City. The City Halls have now become the permanent home of the BBC Scottish Symphony Orchestra and the Scottish Music Centre and will host regular concerts by the Scottish Chamber Orchestra.
CableNet was originally specified by the project's theatre consultants Arup Acoustics, as the safest and most effective way of providing high-level access across the entire roof void.
Arup's Ray Carter first approached Slingco back in 2001. It was interesting from a structural viewpoint explains Slingco's Nick Dykins, with the CableNet design having to be rigged amidst the original timber roof trusses and work integrally with the building's roof structure. The frames are supported by these trusses with their brackets straddling the bottom shard of the timber truss. They also stipulated that no intermediate CableNet members to be visible from the underside.
The CableNet grids are sized approximately 10.9 metres by 3.3 metres - with each one being very slightly different to account for fluctuations in the roof timbers. The grids are engineered to work in a back-to-back fashion .... the frame side members form horizontal trusses over the bottom member of the timber trusses allowing a lighter section to be used for absorbing the loadings from the tensioning of the cable assemblies.
Constructed from 3 mm wire, this CableNet installation will support a total load of 3.6 tonnes distributed over the 10 grids, 360kg per frame. On the underside, the grids are separated by cosmetic plastered roof panels, so from the hall below it looks as if there are 30 smaller Nets. A four-person team from Slingco completed the installation in two weeks.
City Halls production manager Graeme Ironside has not worked with the Slingco CableNet before, he says: "It makes life so much easier both in terms of access and moving equipment around." Hoists rigged through the grid make it incredibly easy to drop things in and out as required.
Another reason for choosing CableNet involved practicalities relating to the overall task of improving the room acoustics. The stage has been lowered to increase the volume of the ceiling area above, aiming to create a bigger and fuller orchestral sound, so it was essential that the grid above would work in as shallow a roof space as possible. Neatly concealed above the grid at the stage end of the Net is a series of acoustic baffles.
Slingco's Peter Downham-Clarke says: "From working out a suitable scheme with Ray at his Judds Farm base in 2001, developing the design to ensure an efficient manufacturing and installation method to carrying out the final inspection on the finished installation in 2006, the job's proved to be one of the most interesting the team has worked on."
The Grand Hall is now being utilised for a full programme of concerts, recitals, recordings and music events and is proving exceptionally popular.
(Chris Henry)
