Expert Consultancy – Sustainability in Structural Engineering Design

It is estimated that the built environment in Ireland is responsible for approximately one-third of our national greenhouse gas emissions. The Irish Green Building Council has found that producing and transporting construction materials and constructing buildings and infrastructure account for 11% of our national emissions. Therefore, decarbonizing the construction industry is essential in addressing the ongoing climate emergency and is now something driven by policy from a central government level and through state agencies and professional representative bodies.

This blog aims to give an overview of the areas where an engineer can have the highest impact in minimising the embodied energy associated with their projects. In structural engineering specifically, significant work has been carried out by the Institution of Structural Engineers (IStructE) in providing awareness, guidance, and tools to promote sustainable development. In a publication by the Climate Emergency Task Group of the IStructE , a Sustainability Resource Map has been produced, and some of its themes are used here to summarise some steps engineers can take.

• Influencing the Brief
• Lean Design
• Low Carbon
• Zero Waste

Figure 1 – Carbon Reduction Curve (Source – Green Construction Board)

 

Influencing the Brief on a project is where engineers can significantly impact embodied energy. The phrase “Build Nothing, Build Less, Build Clever, Build Efficiently” is a hierarchy of how engineers should approach a brief and, with this in mind, help to influence areas with maximum benefit. Figure 1 shows the concept of a carbon reduction curve based on this hierarchy of decision points and the potential to reduce emissions at each project stage.

While building ‘nothing’ or ‘less’ is counter-intuitive in terms of development, this can be achieved through the re-use of a building rather than demolition and reconstruction. For example, could floors once designed for commercial space be re-used as residential, and are original structural designs capable of this change in use? In more complicated cases, justification of load-carrying capacity by innovative approaches such as detailed investigation and analysis can help find capacity or prolong the safe use of a structure.

Figure 2 Example of Reinforced Concrete Embodied Carbon

Lean Design refers to the design of buildings while being conscious not to be overly conservative with designs. Designers should consider if it is possible to make changes such as reducing concrete content or cube strength or prescribing a 56-day strength rather than a 28-day strength.

As serviceability limits often dictate design decisions, designers need to be aware that simple changes such as optimising spans around building facades effectively ensure the building is performing closer to its ultimate capacity and performance are not driven by serviceability alone, thus promoting a lean principle.

Low Carbon. Graphics shown in Figure 2 indicate the typical embodied carbon within structural concrete constituents. Designers can use graphics like this to become aware of sources of embodied energy and make decisions between various schemes with this in mind.

Life cycle information (commonly carried out as Life Cycle Assessment, LCA) can be compiled to calculate the embodied energy of alternative scheme designs to allow for comparison. Various bodies have prepared Guidance and tools that describe a consistent method for carrying out these calculations , . Figure 3 below shows an LCA’s typical components, including the five stages A to D and their constituent modules. Embodied carbon can be calculated for each module and then expressed in general terms over one or more stages – typically as ‘cradle to gate’ (A1-A3) or ‘cradle to grave’ (A1-C4).

 Figure 3 Life Cycle Assessment Stages

Zero Waste. Some of the means to reduce waste include the circular economy concept, re-use of existing buildings, and modular construction in factory conditions.

The circular economy has gained a lot of attention recently. Building design decisions can be made with circular principles in mind, such as the ability to re-use materials, designing for future de-construction and material salvage as opposed to demolition, and extending the life of a building by refurbishing but retaining the main structure. This last point might be achieved by extending vertically but retaining foundations or using a grid that does not limit future use. A concept known as the ‘Shearing Layers’ of a building introduced by architect Frank Duffy and later developed by Stewart Brandt describes how layers should be independent to promote re-use and refurbishment without fundamental changes to the structure. Figure 4 shows how these six layers are viewed.

Modular construction is now commonplace in Ireland, particularly with significant developments where gains can be scaled. Economic and programme objectives may have once driven this; however, the reduction in waste due to factory conditions and the ability to incorporate sustainable material choices now means sustainability will also drive this form of construction.

ORS is now incorporating sustainability into design decisions through the use of concepts and tools referred to above.

Figure 4 – Stewart Brand’s ‘Shearing Layers’

References

	Irish Green Building Council, “Whole Life Carbon in Construction and the Built Environment Ireland,” 2021.
	Engineers, Institution of Structural, “Climate Emergency Task Group – End of Year Report 2021,” 2021.
	O. J. Gibbons OP, How to calculate embodied carbon, London: Institution of Structural Engineers, 2020.
	“Irish Green Building Council,” . Available: https://www.igbc.ie/planetary/.
	S. Brand, How Buildings Learn: What Happens After They’re Built, New York: Viking, 1994.