The tallest built structure in the world up until 1311 was the Giza pyramid, constructed in 2600 BC. Even after this date, the world's tallest buildings – normally cathedral spires in Europe and the UK – remained no more than 150 to 160 metres high right up until the end of the nineteenth century.
The Industrial Revolution generated technologies that permitted the mass production of materials and enabled extraordinary increases in the scale and height of construction. Through this period and into the twentieth century, the relationship between labour and material costs in construction gradually reversed. Labour costs increased exponentially, albeit with massive variations in the distribution of wealth. At the same time, astonishingly, material costs stayed almost constant.
As a result, the pre-industrial construction methods, which were generally labour intensive, with material use reduced as far as possible, were gradually replaced. Instead, methods that minimised labour took over. Tiled masonry vaults, built in Europe since the Middle Ages and made famous on the east coast of the United States in the nineteenth century by the Spanish entrepreneur Raphael Guastavino, were rendered uneconomic by their high labour costs in the early twentieth century, and replaced by reinforced concrete shells. More recently, loadbearing walls made of bricks or stones laid by hand have been replaced by prefabricated brick slips cast into concrete panels and attached to a structural frame.
This profound shift in construction economics is inconsistent with our current climate crisis. If the cost of a structure was proportional to its carbon footprint, then optimising for minimum cost would be consistent with optimising for minimum carbon. Although the two variables are linked even now, their relationship would become closer if we properly accounted for the negative externalities of carbon, and in particular for the combustion of the fossil fuels involved in making materials.
A profound change in the way we approach structural design is required, and even if the goals and the overall themes are clear, the precise details of the most efficient solutions are still evolving. Will cement be replaced by another material, or improved such that the use of carbon intensive Ordinary Portland Cement becomes dramatically reduced? Will we rethink the standard engineered timber truss, or the reinforced concrete flat slab? And will optimisation for carbon become standard practice in the conception as well as the delivery of new buildings?
This special issue of the Structures and Buildings Journal sets out to address these subjects.
It starts with a call to arms both written and by video from Ibell and Russell (Ibell and Russell, 2023). They confront us with the radical change in education required for the next generation of civil and structural engineers. A graphic can transmit a message more directly than words, and Ibell and Russell's first figure leaves no doubt as the scale of the change in the design philosophy that engineers of the future need to adopt.
Schematic illustration of anthropogenic fossil-fuel related carbon dioxide emissions into the atmosphere, starting from the industrial revolution (Ibell and Russell)
Schematic illustration of anthropogenic fossil-fuel related carbon dioxide emissions into the atmosphere, starting from the industrial revolution (Ibell and Russell)
Staying at the overall industry scale, Dunster and Marriott (Dunster and Marriott, 2023) have set out the opportunities and considerations to bring in new lower carbon cementitious materials into widespread use in the UK. Given that cemetitious materials are the most heavily used construction materials worldwide, it is essential to urgently reduce their carbon footprint. The knowledge of practicing engineers is often strongest in their core skills of design and analysis and the specification of materials has received comparatively little attention in the current environmental debate. Greater consideration to this, and in particular a focus on alternative cementitious materials, could significantly reduce the embodied carbon of a building.
As the environmental debate matures, it is essential to appraise the wealth and quality of new information being produced. An increasing number of material suppliers are providing Environmental Product Declarations (EPDs), almost unheard of a few years ago. Anderson and Moncaster (Anderson and Moncaster, 2023) compare EPDs to evaluate the balance of renewable and non-renewable energy as well as the efficient use of energy in the production of cement, brick, and timber products.
The second set of papers closes in on specific subjects across the industry.
Frangedaki, Sardone, Marano and Lagaros (Frangedaki et al., 2023) review the evolution of optimisation processes in architectural and engineering design, and present different strategies for introducing parameters for a variety of different architectural, environmental and structural variables.
Costa, Oval, Shepherd and Orr (Costa et al., 2023) propose a specific low carbon design solution for floors – the element with the largest contribution to structural quantities in most buildings. Expanding on existing research into this important field, they focus on the design, development and construction of a thin segmented shell. The paper describes the computational framework that was developed during the process.
The final paper is also a specific proposal for a more carbon efficient structural system. Chahade and Schober (Chahade and Schober, 2023) have evolved and tested a composite connector for timber trusses. The new type of connector that they have developed enables trusses to be created in roundwood, which has structural benefits over other engineered wood products.
