A complex project that called for a variety of trusses demonstrates the flexibility and cost-effectiveness of Mitek’s steel roofing system
Light steel frame (LSF) roof structures can themselves be considered architectural wonders as a training facility in Mpumalanga illustrates.
The Kingdom Leadership Centre, a training and education facility developed by the Joe Singh group, required a complex, curved ultra-span LSF roof structure. The challenge was to build a scissor bowstring truss over a 20m clear-span section with additional mono bowstring truss sections on either side, making a total building width of 42m. To complicate matters, the client wanted the roof structure to combine two end-projecting, dog-leg hipped roof sections, with the main roof section on a fully curved end wall.
‘This was a particularly complex job,’ says Uwe Schlüter, general manager of the Ultra-Span (LSF) division at Mitek Industries South Africa. ‘But ultimately this project showcased how flexible Ultra-Span LSF steel is, and how it makes it possible to design and erect a complex roof safely, cost-effectively and on time.’
He believes that this is only possible if the contracting company has the requisite skills, adding: ‘In this regard, I must complement EcoStruct’s Jacques Cloete who designed this structure on the Mitek 20/20 roof design and engineering software with full 3D resolution, which certainly helped to achieve all the complex curves and roof lines.’
The result is an extremely lightweight 3 250m² roof structure using just 8.7kg/ m² of LSF sections, roll-formed using ArcelorMittal’s high-strength galvanised steel sheet. This means a total mass of only 28.3 tons of LSF for the entire roof structure.
According to John Barnard, director of the Southern African Light Steel Frame Building Association, one of the keys to this project was the assembly of ‘clusters of trusses’ on the ground, which significantly improved the safety of the process. The process was also speeded up by using a mobile crane with a long reach to lift the trusses into place. ‘The combination of low mass, safety and speed translates into cost-effectiveness,’ says Barnard.
EcoStrut used a 160 ton mobile crane to lift five pre-assembled braced roof truss clusters into the final position simultaneously. According to Barnard, it took only one day to lift all 46 trusses of the main roof into position, ‘greatly reducing the total time spent on site’.
The unique profile shapes of the Mitek Ultra-Span roof system ensures a low mass per m2 (between 6–10kg/m2), thereby saving on the supporting structure and on the transport and erection costs.
Large sections of the roof can be pre-assembled on the ground and hoisted into position on the roof – making this one of the most viable roof systems in the range of 15m to 40m clear-span structures.
This project is an excellent testimonial for LSF roofing. It illustrates the beneficial aspects of steel – formability, guaranteed high strength, low mass, straight and true elements, narrow tolerances, ease of transport, handling and erection, with life-long corrosion protection supplied by the galvanised coating. In addition, the cost of the light gauge steel roof structure was lower than timber trusses, or welded heavy steel trusses.
The use of light steel roof structures – such as Ultra Span – is growing rapidly, replacing timber, and even competing with heavy steelwork in some cases.
Nothing emphasises the coming-of-age of light steel frame building in SA more than the record number of project entries for Steel Awards in 2017.
There are many advantages to using the Ultra Span light gauge truss system:
It is an elegant and simple system, with all members straight and true for a level roof
It has a span capability from small and low-cost, to large 40cm clear-span commercial structures
It comes in kit form for low-cost housing or remote projects
The roofing system will last a long time due to its galvanised coating plus its inherent properties of non-combustibility, and resistance to borer and fungus attacks
Its lower weight reduces transportation costs and improves handling and erection
The trusses can be assembled with screws and an electric fixing tool directly on site or in factory conditions.