Sandton City contractors win steel awards
For their role in the striking new Protea Court rooflight at Sandton City, joint venture contractors Aveng Grinaker-LTA and WBHO recently took top honours in the annual Steel Awards hosted by the Southern African Institute of Steel Construction.
This impressive rooflight is 44m in diameter and the entire structure is sloped at 11 degrees, explains Andrew Owens, managing director of Aveng Grinaker-LTA Building. Challenges abounded in its installation.
"The design of the rooflight structural steelwork frame is extremely complex, and due to the nature of the roof covering, the tolerances of the structural steel installation had to be kept to 3mm," Owens notes. "The main roof beams are radiused, tapering plate girders that run at 30 degrees to each other.
The beams span up to 27m and are supported by an internal concrete tower and externally on a latticed box girder. Only with the experience, competence and close cooperation of the consulting team, main contractor and specialist structural steel contractor was it possible to construct the challenging structure from the extremely complicated 3-D design."
In evaluating this entry, the judges of the Steel Awards commented: "In assessing excellence in the use of steelwork, in all aspects – architecturally, structurally, the manner in which all the challenges have been solved and just sheer excellence – there is no doubt that the Protea Court rooflight in Sandton can take its place as an overall winner, with pride, amongst its predecessors."
In addition to its award-winning steelwork, the Protea Court rooflight also features other technical innovations. It is clad with a total of 170 translucent Ethylene Tetraflouroethylene (ETFE) cushions that are kept permanently inflated with compressed air. Each cushion is restrained within the network of profiled aluminium extrusions that have been curved to the shape of the steel structure.
The aluminium sections are fixed to all of 1 468 steel support ‘T’-brackets that were required to be surveyed independently in a three-dimensional plane to tolerance of 3mm.
"Achieving the tolerance was crucial to ensure that a quality installation of the ETFE cushions was achieved," Owens states. "This application is a first in Southern Africa, and the services of an experienced specialist contractor were employed to supply and install the innovative product."
Another construction first at Sandton City can be found in the steel latticed box girder supporting the steel roof structure, which is supported on 12 bifurcated columns of various heights. The lattice box girder is clad both externally and internally with an innovative product called Decolite, as are the steel rooflight’s main radiused girder beams and the bifurcated columns.
Decolite is a light-weight cladding system that consists primarily of polystyrene wrapped in a robust polyuria shell. The finish to the Decolite internal cladding of the gutter beam and bifurcated columns is high gloss, which, Owens notes, has never been achieved before and is yet another first time application.
The Sandton City Repositioning Phase 1 construction project was awarded to the Sandton City Joint Venture in June 2009.
The project comprises primarily of the construction of an extension to the South East corner of the existing Sandton City Shopping Centre; a refurbishment to the existing shopping centre's malls and covered parking garages; an upgrade to the existing shopping centre's mechanical and electrical networks; and the construction of a new parking deck over the existing roof top parking. This phase is due for completion towards the end of October 2011.