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A look at the sustainability of steel structures

by Darren
a look at the sustainability of steel structures

The pressure is mounting, both locally and internationally, on industries to radically reduce their greenhouse gas emissions and the construction industry is not excluded from this demand. Steel has been in use for hundreds of years and this well-known construction material might just offer possible answers to the quest for sustainability in the industry as engineers and architects are urged to think about the long-term implications of their choices.

In the UK’s steel sector, Tata Steel, the British Constructional and Steelwork Association (BCSA) and the Steel Construction Institute (SCI) is leading the way in developing a more sustainable construction industry for the country. This sector argues that steel is one of the most sustainable of the major structural materials. The low waste, flexibility, off-site manufacturing, speed, resource-efficiency, adaptability, ability to deconstruct, long-lasting appeal, safety, reusability and recyclability are all benefits of steel wherever it is used. According to the UK’s steel sector, these natural qualities result in many social, environmental and economic benefits to satisfy sustainability’s triple bottom line.

Locally, Dr Hennie de Clercq, executive director of the South African Institute of Steel Construction (SAISC) is just as vocal about the many benefits of using steel as a sustainable structural material. “Besides steel’s reliability and accuracy in the structural process and the longevity of the product, it has limited environmental impact and can be renovated and changed. Steel structures can literally be taken apart and reused at a different building site for another project.”

Steel’s carbon footprint
Before one can determine the carbon footprint of steel, you have to make sure that you are making a fair comparison. It is important to consider whether data is derived from a limited “cradle to gate” analysis or from a full product life cycle.

According to information provided on the World Steel Association (Worldsteel) the data collection and methodology for calculating the life cycle inventory (LCI) for steel products, the CO² emitted during the production of one tonne of a structural section is 0,76 tonnes. This value is higher than some other structural materials on a ton-by-ton basis, but Tata Steel, Europe’s second-largest steel producer, states that a ton of steel goes a great deal further than other materials, so the actual carbon footprint of the structure is lower.

Worldsteel calculated the value of 0,76 tonne using the system expansion methodology (the most comprehensive assessment method currently available and the preferred approach of the ISO 14040 series of environmental standards). There are other values in circulation, some are lower and others higher, but most are derived by less rigorous methods than the system expansion, which attempts to have a common method for all materials. The method intends to provide a fair comparison and takes into account steel’s unique environmental qualities. Steel also has a high strength-to-weight ratio, which means that the weight of steel required for any given application is often much less than for the alternatives.

When calculating the CO² emissions associated with steel production, the system expansion method credits manufacturing processes for co-products that save energy and emissions, such as process gases being used to generate electricity. Credit is also given for the net CO² that is saved when a product is reused or recycled. While every fabricator must determine its own carbon footprint in the manufacturing process, the BCSA has developed a common methodology for calculating the carbon footprint of the steel fabrication process. Initial evidence from a selection of carbon footprinting assessments indicates that the answer will be generally be in the order of 0,3 tonnes CO² per tonne of fabricated steelwork.

From the cradle to the grave: the whole story of steel’s life cycle
Steel also has sustainability benefits at its end-of-life because steel structures are inherently reusable in full or part. Complete buildings can be taken down and rebuilt elsewhere or individual elements can be reused. Tata Steel indicated that an increasing number of buildings are being designed with this in mind, but reuse is an option for steel structures, even without any special provision.

Steel is also not like most other materials that can be recycled only once or to a lesser use, which is also known as down-cycling. Steel can be recycled indefinitely without loss of property or performance. The multi-cycling of steel is supported by a well-developed and efficient scrap-collection infrastructure. It can be recycled at end-of-life to form products that are of the same or even a higher quality as the original material. Most steel components are large and easily captured. Capture rates vary depending on the ease of extraction from the demolition site, but on averages 94% of all steel components are recovered. This average might even be higher in poorer economies where the relative value of steel is higher. It means that steel always has a value, which guarantees that virtually none is of it is ever disposed of to landfills. According to Tata Steel, a recent survey indicated that no more than 1% of structural steel ever goes to landfills.

The multi-cycling of steel is a self-sustaining system that predates modern appreciation of environmental issues and would continue in the unlikely event that these issues should lessen in their importance. Tata Steel says over 500-million tonnes of steel are multi-cycled worldwide each year, an equivalent of 180 Eiffel Towers every day.

The American Institute of Steel Construction (AISC) recently looked at the life-cycle costs on the average annual maintenance and repair of open, above-ground, multi-level parking structures that are framed in structural steel. According to the institute, steel-frame structures’ maintenance costs compare well with the industry norm and in some cases a saving of 40% was incurred. High-performance coatings and galvanizing systems also add to the superior long-term corrosion protection for exposed structural steel. A structural steel frame that was coated with a high-performance multi-coat paint system using a zinc primer can be expected to perform well with little maintenance for 25 to 30 years. Some parking-structure owners in the US chose to protect their structures by using galvanized steel that provides effective protection from corrosion in excess of 40 years. The AISC said an added benefit of a galvanized surface is that it can be painted for aesthetic purposes and it will further enhance durability.

Thermal mass
The thermal mass of a building can be used to reduce the requirements for active heating and cooling. De Clercq states that studies in the UK and and USA showed that multi-storey buildings with steel structures have sufficient thermal mass to influence diurnal temperature variations. With light steel framing, however, a study commissioned through the Council for Scientific and Industrial Research (CSIR) confirmed that using steel framing positively affects the thermal behaviour of a building, and especially the amount of energy required to maintain year-round acceptable temperatures in a house. “Using steel framing can result in energy cost cuts of up to 30% for the cooling or heating of a building,” he says. De Clercq states that the institute recently received practical confirmation of the research at the Deloitte office site in Garsfontein, Pretoria, where light-steel frame cladding resulted in less air-conditioning needed for the building.

Cost-effectiveness: the economic benefits of steel
To be sustainable, a solution needs a sound economic basis. Tata Steel describes steel as fast, efficient, predictable and safe. Production is highly automated and site operations are not labour-intensive. Steel offers a cost-effective solution, while offering long-term value through flexibility, adaptability and a lasting appeal.

Steel is widely considered as a fast, safe construction material. Reduced time on site means lower costs, quicker profits and less disruption to the local community affected by the building site. Steel is also manufactured off-site in a factory environment and arrives only on site when needed, making it a very accurate material that is predictable with little room for error. There is also no site waste and any waste that is generated earlier in the process is easily returned to the steel-supply chain.

A case study of sustainability
According to Tata Steel, the Prologis set itself high sustainability targets for its future distribution facilities. Prologis Park near Stockley Park, Heathrow, is an excellent example. Barrett Steel Buildings supplied this 5 500m² warehouse and it was designed so it could be disassembled and reused on another site, even down to the level of the ground beams.

The two-storey structure is 99m long. It is manufactured in the form of a two-bay portal frame and has an adjoining office space. The high-bay portal frames span 24m in two bays and allow 10m clear space to the underside of the haunch. All steel members are stamped with section size and grade to allow them to be identified for reuse. It is estimated that a total of 80% of the components can be reused, while 80% of the portal frame structure is reusable. About 95% of the floor beams and 100% of the galvanised steel components can also be reclaimed.

Barrett Steel Buildings walked away with the BCSA’s Gold Sustainability Charter for this. The company also had an independent assessment made of its own carbon footprint as a manufacturer and steelwork contractor, reported the Tata Steel website.

Closer to home and more recently, Moyo on the Pier at uShaka Marine World also illustrates how steel structures can perfectly address the need for sustainable functionality. The overall flexibility of the site, both in terms of the pier usage and Moyo’s ability to relocate the restaurant, had to be maintained and called for a sustainable solution. Reversible connections were adopted in the structure. Furthermore, the team opted for a construction sequence that was easily demountable so that deconstruction could take place with no damage to the steelwork.

No wet work, painting or dirty construction methods were allowed on the pier due to the tough environmental regulations, which only added to making steel the preferred construction material on site. According to SAISC, the professional team feared that Moyo on the Pier would never be built but when the project finally received the go-ahead, they only had five months from design development to the delivery of the building. The fact that it was delivered on time is a tribute to the client, professional and contracting team, as well as the benefits of steel.

A positive outlook
Tata Steel says people like a steel-built environment which is adaptable, airy, light and open. Steel structures also do not deteriorate or decay. With steel’s long clear span, interiors can be changed easily, while steel frames can be adapted to give old buildings a new lease on life. The longevity of a building is fundamental to its overall sustainability and steel structures offer this.

As the markets start to settle, the need and demand in the building industry will grow. Local official statistics already show there has been a 4% growth in the area of building plans approved during 2011, which could herald increased building activity towards the end of 2012. “In general, we have also noticed a much greater demand for steel structures, certainly at the conceptual stages. We believe that this upsurge in steel utilisation is largely driven by the need for environmentally-friendly materials,” says Uwe Schlüter, business development manager of MiTek Industries.

Full acknowledgment and thanks are given to Dr Hennie de Clercq of SAISC, MiTek and Tata Steel Construction for the information used in this article.

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