27 May 2021
Technical
Designing steelwork with hollow sections in a climate emergency
Structural hollow sections and sustainability

“We are living in a climate emergency.” 
This is the term that scientists agree best represents the current situation with respect to climate change.

People around the world, in both their personal and professional lives, are making changes to help minimise and mitigate the harmful effects of climate change.

As material producers, engineers and designers, we shape the future of the built environment every day, so it is vital that we act now, together, for a more sustainable future.

Although we can all make changes in our daily lives, the impact of intelligent design, both on the “embodied” impact of construction and on the “lifetime” impact of the built environment, can be far greater and longer-lasting. That is why it is not scientists, but engineers who are really at the forefront of tackling this climate emergency.

With the importance of sustainability in design, judging what are the “embodied” and “lifetime” impacts of certain design decisions has become a critical topic and nowhere more so than where structures are concerned. An increasing number of material suppliers are now providing Environmental Product Declarations (EPD’s) but there are also industry average EPD’s and the IStructE are now also providing guidance. So where to look? How to compare? And are there some simple rules of thumb which can help?

The first point to note is that the basics of good structural design remain the same. That is to provide the most efficient structure within the brief. Efficiency in design generally goes hand-in-hand with minimised environmental impacts. Particularly for steel weight is a good proxy for embodied impact. So designing to minimise the mass of structures will generally be a good start if wanting to minimise environmental impact too.

Structural steel is available in a variety of shapes and grades, but the largest part of the environmental impact, particularly in terms of climate change, is from the steel-making process itself. Different structural grades from low-strength S275 to the now-standard S355 up to high strength S460 and beyond display very little difference in their embodied impacts, with these higher strengths being achieved through only small additions of alloying elements as well as clever processing.

Typical mass of steel required for sustainability

In a previous blog, we demonstrated how the savings in steel can add up. A hollow section can be intrinsically more efficient than an open section and a hot finished section to EN 10210 (such as our Celsius® range) is more efficient than a cold formed section. But to take it even further, our Celsius® range is now available in high strength S460NH steel, enabling further light-weighting and at least 20% steel savings in many applications. By using this combination of approaches, up to 50% of the steel-weight could be saved from certain steelwork elements, resulting in an instant 50% saving in embodied emissions.

Our new Celsius® design app provides a quick and simple tool to help ensure the optimum use of Celsius® hot finished hollow sections. In contrast to traditional tables of loading capabilities for each section size, the Celsius® app allows the user to search based on the required design load and view qualifying sections side-by-side to maximise efficiency and minimise environmental footprint.

Having achieved efficiency in design, accounting for that benefit, and indeed accounting for what remains of the environmental impact of a project, becomes the next major challenge.

Many organisations are now starting to set targets for projects such as “Embodied CO2 emissions per m2 of floor-space”. So even allowing for efficient design, a new skill of “carbon-budgeting” is now called for. Unfortunately, unlike structural design, the rules of carbon budgeting are not yet well defined.

The significant focus, in minimising and mitigating the harmful effects of climate change, is carbon emissions and intensity and the principle unit of measure for this is mass of CO2 emitted – or more accurately CO2 equivalents (because certain other gases can also impact our climate, but it is all converted into equivalent mass of CO2). 1kg of CO2 emitted anywhere in the world will have the same impact on climate change, so this is a truly international and transferable measure. But how do we know the impact of our structural steel? And is all steel the same?

Like many construction products, many steel-makers now produce EPD’s for their products. These detail the specific environmental impacts, associated with the production of 1kg or 1 tonne of the product, through the specified production route. It is important to ensure that EPD’s are third-party verified (Type III) and produced in accordance with the relevant ISO standards (ISO EN 14025 & 15804) but even then, there can be big differences between what is actually reported.

The EPD framework is designed to report on the whole life cycle of the product.  There are up to 17 life cycle stages defined within the framework, but not all are always reported, in many cases for very good reason. For example, as a producer of structural hollow sections, it is not relevant for us to define an impact for our product during the ‘use phase’ as it could be used in many different ways and therefore potentially incur very different impacts. For this reason, many construction product manufacturers only report the Production phase of the life-cycle (so-called Modules A1-A3). However, it is equally important, and indeed required in the latest standards, to also consider what happens to the product at the end of it’s first useful life (Modules C and D).

Recycled steel life cycle

Our actions in a climate emergency should not store up problems for future generations. Likewise, if materials we use now can be of use to future generations, we should give them credit where it is due. That is very much the case for steel. A survey of demolition sites1 found that more than 99% of scrap steel from demolished buildings is either re-used or recycled. As such, steel, particularly when used in construction, is a material that enables the circular economy. So it is almost certain that any steel made today will be used again at some point in the future, avoiding the need for primary steel-making in the future. The same cannot be said of virtually any other construction material.

This is why it is essential that Module D (which equates to the circular economy) in particular, is included in any “carbon accounting” – to ensure that what happens to a material after its first intended life, is fully taken account of.  To not account for the benefits of circular economy (or Module D) in our calculations effectively treats circular economic products the same as products that will end their life in landfill.

If looking just at “Module A1-A3” emissions for different steel products, some very different values for CO2 equivalent emissions can be found. This can be based on the steel-making technology used (usually referred to as EAF or BOS production). However, when the full life-cycle impact is calculated, the reported emissions of different steel products become much more aligned in terms of carbon intensity.

With differences in full life-cycle emissions between similar steel products or steel producers relatively small, at the design stage of a project, when the actual supplier will be unknown, it is usually better to consider all steel products as similar from the point of view of CO2 emissions. IStructE now provide guidance on some typical figures to help the design-phase carbon accounting, but just as important at the design stage will be the issue of availability in the local market.

When specifying hollow sections, use of the Celsius® design app can give some peace-of mind here, since only section sizes produced by Tata Steel and supplied through our extensive distribution network are included in the app. Taking it one step further, the app includes a real-world availability indicator for each section size, based on our experience of supplying through our network, so it is easy to be sure that efficient designs aren’t likely to be changed once they get to the procurement stage.

So there are three key lessons on designing in a climate emergency:

  1. Efficient design is still the number-one goal for the engineer (often called ‘using less stuff’);
  2. It is essential to consider whole-life carbon accounting, rather than just looking at limited life-cycle stages (otherwise we treat circular materials the same as landfill materials);
  3. And be aware of any likely availability issues up-front to ensure that an efficient design is realised in construction.

To explain these issues more fully, we are now delivering a new CPD aimed at engineers: “Sustainability and Structural Hollow Sections – decarbonization in a climate emergency”. To book an appointment for one of our engineers to provide this CPD training, either online or in-person, please get in touch.

And our Celsius® design app is available to download for either Apple or Android – search 'Tata steel Celsius' in your app store.

 

 

1. As part of a Eurofer led project, Tata Steel approached UK National Federation of Demolition Contractors for recycle and reuse rates.  The Eurofer study covered all of Europe but most returns to the survey were received from the UK.

 

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