Mechanical Technology January 2015

⎪ Special report ⎪

1

In this special report, MechTech summarises the steel construction project winners from last year’s Steel Awards 2014, hosted by the Southern African Institute of Steel Construction (SAISC). Excellence in the use of steel

access the structure without damaging the trees and the bush, reached the site. The judges concluded that the deter- mination of the whole team, the quality of their work, the fact that when you visit the site the roof is not visible from more than a few metres away, and that the construction team left the site virtu- ally as they found it, made this project “excellent in the use of steel” for every possible reason. Category winners No. 1 Silo, part of the first phase in the Silo precinct development of The V&A Waterfront, won the Architectural category. This 10-storey development consists of an east and west wing built on two levels of a mega-basement cov- ering the whole site. Structural steelwork was the solu- tion to provide slender support to the facades, walkways, bridges, lifts and feature stairs, while economically extending the cantilevers of the con- ventional post-tensioned slabs framing the atrium. The roof of the atrium is positioned above an open volume area spanning 17 metres. A composite steel and con- crete Bondek slab was designed to serve as the primary support and waterproof- ing line to an accessible and functional roof. Another critical design element of the atrium was the feature staircase that served the five office levels. Heritage requirements regarding the treatment, restoration and reinstate- ment of the existing structures were of the utmost importance and underpin-

S uch was the quality of the steel structure at the Malapa fossil excavation site, which was the overall winner and winner of the Association of Steel Tube and Pipe Manufacturers of South Africa’s Tubular category, that Steel Awards 2014 con- venor, Spencer Erling was prompted to say: “It is surely the first time since I have been managing the Steel Awards process – this year is number 13 – that the overall winner has ticked so many boxes as to why this project represents excellence in the use of steel.” In 2008, Professor Lee Berger of the University of Witwatersrand was using Google Earth to look for possible fossil deposits in the Cradle of Humankind. What caught his eye was a nearly circular ring of trees, something that indicates a possible cave entrance or potential fossil deposit. The rest is paleontological history. The brief for the Malapa fossil ex- cavation site was to build a removable structure over the dig site to protect the site and the exposed fossils from the extremes of the weather and to allow for as much ‘dig time’ as possible. It had to also blend in with the ring of trees and the rest of the bush on the hillside The structure had to, in addition, have a tourist-viewing platform, a crawl hoisting structure to lift rocks weighing up to one ton, and maximum possible natural light had to be able to

penetrate into the covered area. The access walkway to the viewing platform had to be like ‘a blanket over a baby’ so as not hinder the movement of the natural wildlife – hence no handrails were permitted. The final shape when viewed from above is like a beetle with eight legs. But how can a structure be designed when one does not know where the founda- tions will be? Enter Peter Fellows, the engineer. It was decided that during construction, once positions were cho- sen, rods would be drilled into rocks around the site, onto which base plates would be welded. This required that the eight support columns be adjustable to suit the plate positions identified. The roof was to be ‘rondavel-like’ in shape but not necessarily round, from which would hang the viewing platform and hoisting structure. The detailing and fabrication of a tubular structure such as this require special skills, which were provided by teams from Spiral Engineering, one of the few companies in South Africa with the capacity to build such complicated structures. To accommodate the site location – with a 7.5 km farm track access road that runs through a riverbed – special trucks with limited capacity were used on the farm. After four unsuccessful tries, a 30-ton all-terrain crane with a long enough radius and capacity to

8

Mechanical Technology — January 2015