Is A Steel Frame Sustainable
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- The use of steel in construction, The sustainability of steel, Sustainable construction, Steel and sustainable construction, Embodied Carbon and Lifecycle Assessments
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One of the questions over using steel in construction is whether a Steel Frame is Sustainable. This article looks at the sustainability of steel and why it is used.
The use of steel in construction
As far back as the 1880s, people were beginning to construct large-scale buildings for commercial and industrial use. However, at the time, when a structure was built to a certain height of about 8-10 stories high, the walls required to support the structure were far too thick.
The solution that builders found was the use of steel buildings, which holds the main load of a building and allows the walls to stay at the same thickness throughout the structure.
The Ditherington Flax Mill was the first structure built using steel construction methods in Britain in 1796 by John Marshall.
It was not necessary to use steel construction to build the mill, but a steel-frame structure allowed for a wide-open space and could fit more workers into the building, increasing profits for his company.
In the modern-day, steel has a wide variety of uses in construction and is not solely for framing purposes. Steel bars are placed into concrete to increase the tension capacity, which is naturally weak.
Steel purlins are built into roofs, supporting the roof between the mainframes. It is also used for the distribution of utilities and the transportation of oil, gas and water.
The sustainability of steel
The production of the steel itself requires a large amount of energy, which may lead you to believe it is not very sustainable if you were looking at that factor alone.
However, steel is extremely durable and is 97% recyclable. It can be recycled many times over without significant loss of quality, making it a feasibly sustainable option for building designers. So ultimately, to assess the sustainability of steel used in construction, we should look at the overall energy used by a building over its entire lifespan.
BREEAM (Building Research Establishment's Environmental Assessment Method) ratings give credentials to a buildings' environmental impact. Certain criteria are assessed within the scoring system.
A building gets several credits for each section. The total amount of credits is then multiplied by an environmental weighting factor, accounting for the relative importance of each section. The overall score ranges from "Outstanding" to "Pass".
Sustainable construction â€“ legislation and drivers
Because of its significant contribution to the UK economy, sustainable construction is an important aspect of sustainable development. It also has a significant environmental and societal impact. The overall quality of life, comfort, security, health, and well-being is linked to the environments we build for ourselves.
The Construction Sector Deal was published in 2019 as part of the UK's industrial strategy. This paper outlines a partnership between the UK government and the industry sector and aims to improve productivity through innovation and a higher-skilled workforce. Included in the deal are four main objectives, including:
a 33% reduced cost in construction
a 50% reduction in the time taken from start to finish for new builds,
a 50% reduction in the trade gap between exports and imports of construction materials
And quite importantly, a 50% reduction in greenhouse gas emissions for the overall lifetime of constructions.
These goals are expected to be met by focussing on three areas. Firstly, the deployment of digital techniques at all phases of design will ensure the delivery of better, more accurate results during the construction and operation phases.
Offsite manufacturing technology helps to reduce the waste and inefficiencies that affect onsite construction, speeding up construction and minimising disruptions. The focus of asset performance will shift from costs of construction to the overall cost of a building during its entire lifecycle.
Steel and sustainable construction
The material properties of steel make it one of the most sustainable construction materials.
Its high strength-to-weight ratio means that you don't have to use a lot of steel in comparison to other materials, allowing designers to create innovative, exciting, and creative new buildings.
Zero carbon emission buildings with high BREEAM ratings are easily achievable with the use of steel in construction.
Steel is manufactured using the most abundant element on Earth, iron. It is easily recycled or reused almost endlessly without compromising the integrity of its material properties.
This useful characteristic of steel gives it a high rating in terms of sustainability at all stages of its lifecycle. Infrastructure for the recovery and recycling of steel has been in place in the UK for decades and is highly efficient. Recovery rates from demolition sites are over 96% of all types of steel.
Embodied Carbon and Lifecycle Assessments
Previously, the assessed impact of carbon has moved beyond simply addressing the carbon emissions of a building during its operational lifetime.
We have recently moved on to assessing the carbon impact of a building during its entire lifecycle, from construction to demolition. As a result, the term "embodied carbon" is now used to refer to the greenhouse gas emissions during a building's complete lifecycle.
This includes the construction of the process itself and the end-of-life aspects such as decommission and demolition.
Embodied carbon is a single element of a broad discipline known as lifecycle assessment or LCA, which accounts for a range of potential environmental impacts such as energy, materials, and end of life processes. It is important to specify the type of LCA used during a lifecycle assessment.
Some use a "Cradle to gate" method, which only accounts for embodied carbon up until the product leaves the factory. Most agree that it is better to use a "Cradle-to-cradle" approach as its generally more robust and accounts for much more than just the manufacturing processes.
This approach measures all lifecycle phases from manufacturing to demolition and disposal via recycling or reusing.
In terms of steel, the high strength and low weight of steel frames reduce the foundational requirements of buildings. Both of which are key factors in embodied carbon.
However, as mentioned above, the carbon emissions due to the energy used during the manufacturing of steel are usually higher than other materials. Fortunately, though, because of its high strength-to-weight ratio, you generally require less steel in a structural frame compared to other materials.
Operational Carbon: Steel and Thermal Mass
Overall, structural form does not typically have a high impact on the operational carbon emissions from non-domestic buildings. Though, thermal mass is one issue that needs to be addressed.
Thermal mass describes the ability of a building to absorb and store heat. When utilised correctly, it can reduce the operational carbon emissions of a building by optimising heat transfer throughout the building, reducing the need for air conditioning.
It is often thought that concrete structures are more energy-efficient due to their greater massing, but the variation of operational carbon impact between concrete and steel frames is less than 1% in all cases. Rather, steel frames provide the optimal slab thickness to fully utilise thermal mass.
A common parameter for assessing the thermal mass of a building is admittance, which defines the ability of a building to exchange heat with a space when exposed to fluctuations in temperature.
The maximum value for admittance can be achieved with only 75-100mm of concrete, showing that it is not necessary to have a high mass of concrete.
For multi-storey buildings, the most important element for accessible thermal mass is the upper floors, which are generally always built using concrete whether or not the building is steel-framed or concrete-framed.
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