Previous Issue: September 2017

Mall of Africa – light steel frame efficiency at its best

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History was made for the light steel frame (LSF) industry in South Africa when Ohlhorst Africa Lightweight Building Solutions were appointed contractors for the design, supply and installation of the light- weight steel facade wall and parapet structure at the Mall of Africa (MOA). “This was one of the largest single phase shopping mall building projects ever undertaken in South Africa and certainly the biggest and most prominent LSF project to date in this country,” says Southern African Light Steel Frame Building Association (Sasfa) director, John Barnard.

The fact is there have been several projects in recent times all over the southern African region that have confirmed the acceptance of light steel frame building (LSFB) as a mainstream construction method for a wide range of building solutions. None, however, is more significant than the massive MOA structure, which required 217 tons of LSF steel and 25 000m² of Saint-Gobain Weber ETICS (external thermal insulation and cladding system) cladding.

Ohlhorst LBS technical and marketing manager, Jacques van Zyl, says that there are many benefits of LSFB and the main considerations in choosing it at the MOA were the speed of the build – the programme required that the building envelope be closed within a few months – and the long-term cost savings. “The LSF/ETICS system ensures weight reduction on the superstructure resulting in significant cost saving on structural steel and concrete. It also provides a durable external cladding with low maintenance requirements further reducing costs over time,” he says.

The quantum of weight reduction is well illustrated by comparing brick with LSF/ETICS. A brick wall has a mass of 450kg per square metre translating into a weight of 11 300 tons over the 25 000m² at the MOA. The comparable weight with LSF/ETICS is an astonishing 10% of this – 1 130 tons! Add to this that it would take 1100 truckloads of bricks against 110 loads of LSF and the logistical advantage of LSF/ETICS on the entire construction process becomes abundantly clear,” says van Zyl.   

The steel used was cold-formed thin gauge light steel frames and, according to van Zyl, what made this project unique was the architect’s requirement for 30mm and 60mm protruding, horizontal bands (some in excess of 100 meters in length) to wrap the building and to be completely in line at a height of up to 25m.

The LSF/ETICS system was used to create the bands and the accuracy of the system made this complex specification readily achievable. “It worked well even over the brick portion of the building as the LSF/ETICS system has a tolerance of between 50mm and 70mm in surface inaccuracies. Overall, it was just much easier to create the bands this way as regular plaster bands, not being as accurate as LSF, are notorious for creating water traps affecting the longevity of the structure,” he says.

Tia Kanakakis of MDS Architecture, the MOA architects, says that the speed of installation was a major benefit on the project and that the LSF/ETICS lightweight walling system is a far more expedient construction methodology than traditional masonry walls. “Being a lightweight product, it is beneficial for use where there are slab loading limitations. I would definitely recommend the system to other architects or engineers – its benefits far outweigh its limitations, which can always be managed” she says.

Gert Visser of HAGE Consulting Engineers, who worked closely with Ohlhorst LSB, says that, from an engineering perspective, one of the biggest challenges on the MOA project were the extra-large openings and unusually high parapet walls – the LSF walls exceed 6m in height and the parapets are just short of 4m-high, and span 8m between columns. The wind load on the roof parapet walls were a serious issue, which was overcome by reinforcing the LSF wall panels with LSF web joists.

“There is no doubt that use of LSF has opened a whole new world for engineers and architects who are now challenged to become more innovative and creative with their specification of LSF. The Mall of Africa is now the benchmark for what is possible for LSF in construction,” says van Zyl.

An important stipulation on the MOA project was a high R-value – a measure of resistance to heat flow through a given thickness of material and the higher the R-value the greater the resistance – for the external cladding in order to meet the energy efficiency and energy saving requirements of the project. In the case of LSF/ETICS system at MOA the R-Value was approximately 3.6 as opposed to the standard R-value of less than 0.6 for a double brick wall.  “Apart from the substantial energy savings over time these R-value levels give the architects the freedom to be as creative and as inventive as possible while, at the same time, reducing thermal losses and keeping ambient temperatures comfortable throughout the year at low cost,” van Zyl says.

He adds that in the middle of summer – and even while it was still a building site – it was palpable how cool the building was. “Those working inside commented frequently on this apparent anomaly!”

Barnard says the facts are indisputable. “LSFB is a very cost-effective building method, with financial savings emanating from significant time savings to complete building projects, less rework, reduced logistical costs –which are of growing importance due to the escalation of transport costs and general construction inflation – and a drastic reduction of rubble on building sites, when compared with the brick-and-mortar alternative. The piles of broken and unused bricks from the brick sections at the MOA were a glaring example,” he says.  

He explains further that LSFB is significantly more energy efficient than more traditional construction methods – both with regard to “embodied energy” of the materials and components, as well as “operational energy” relating to heating and cooling of the building over its design life. A research project carried out by the CSIR indicated that a LSF residential building will require less than half of the energy needed to heat and cool a masonry residential building to comfortable internal temperatures. “Furthermore, from an environmental perspective, steel is infinitely recyclable.”

Barnard says that the steel consumption of the LSFB industry has achieved double digit annual growth rates over the past five years. “The biggest growth area is in multi-storey office and commercial buildings, where it is replacing heavy masonry curtain walls and, looking at the advantages and the successes of LSFB at the MOA, one can understand why this is the case.”

Van Zyl says the entire team is very proud of this award-winning achievement (the MOA was a joint winner of the Light Steel Frame category at Steel Awards 2016). “This was indeed a project of real class and will remain an example of the massive advantages of the LSFB method in a changing world where costs are spiralling and construction efficiency is the name of the game.

Back Issue: November 2016