By Marc Easton – Senior Structural Engineer – Arup
There are many reasons, from heritage to environmental, why building tall isn’t always the right approach. And yet the unparalleled opportunities tall buildings provide, especially in light of a growing dependence on cities, means their popularity continues to reach new heights. Among other advantages, skyscrapers provide solutions to high-density areas, freeing up other zones for natural and low-rise neighbourhoods and decreasing urban energy use (Resch & al, 2016).
According to the UN, last year 56.2% of the world’s population was urban, with 83.6% of North Americans living in cities. This is set to increase, with 70% of the world’s population expected to live in urban areas by 2050. With the modern city relying on the skyscraper to function, this expansion of urban living means we will inevitably become more and more dependent on tall buildings.
Therefore, as we look to tackle the climate crisis, questioning the construction of skyscrapers is narrowminded. The real focus must be on how they can be built in the most appropriate and sustainable manner.
This means futureproofing tall buildings – recognising their functionality while avoiding vanity projects. This approach will ensure projects retain their value for the next 100+ years. Fortunately, history proves the longevity of tall buildings – no building above 220m has been voluntarily demolished. Where they have been, it has generally been because the potential value of a new building on the site outweighed the value of the current asset.
Tall buildings have a key role to play in a sustainable city and so we need to make it as easy as possible for future users to adapt them as they see fit. Let us then look at three ways we can influence a tall building’s potential value at the design stage, giving it every chance of being retained for decades to come.
Flexibility
The superstructure of a new building can contribute to half its up-front embodied carbon, with the foundations contributing another 25%. We should therefore focus on persuading future users not to remove them and instead encourage repurposing. This means that considering flexible usage at the design stage is vital.
Sustainably-designed floors can become more efficient by minimising the quantity of materials used – and, in turn, embodied carbon. Floor loads should be reduced based on realistic predictions, whilst also factoring in high point loads and hotspots. These zones can provide the flexibility for future use or construction without wasting material on the entire floorplate.
https://www.weforum.org/agenda/2020/11/global-continent-urban-population-urbanisation-percent/
https://www.independent.co.uk/asia/cities-skyscrapers-world-bank-b1858063.html
Vertical structures and foundations can accommodate flexibility with lower impact. Designing these elements with capacity in reserve allows for greater adaptability, as well as capacity for possible increased wind loads resulting from climate change. This is particularly important for foundations that are difficult, if not impossible, to strengthen.
Our aim should always be to achieve long life and avoid demolition. However, if a tall building is demolished, we want to ensure that any remaining parts are reusable. Even small changes can make a big difference in increasing the resilience of buildings for the future.
Deterioration
At more than £500/m2 GFA, one of the most expensive items during a tall building renovation is the façade’s potential replacement. Fortunately, considering specification during design can help extend its useable life and reduce later costs. In addition, circular economy principles are driving the market and in turn improving its performance. An example is 1 Triton Square in London, where 3500m2 of façade panels were refurbished and reused. Compared to the new build alternative, this contribution helped towards the total saving of 40,000t CO2.
Applying appropriate specification control during construction with a good maintenance schedule helps prevent severe deterioration of the structure – which is avoidable when managed correctly. For example, concrete has the potential to last much longer than its initial design life through tweaks such as using an appropriate cover, while steel should be painted to the right specification and timber kept away from water. These are easy wins for any building, not just those over 200m.
Information
Technology has never been more accessible and at such low cost. But to reap the rewards, we need to take full advantage of its capabilities by feeding back once a building is operational. Almost every building today is designed and documented using a BIM package. We share these models throughout the design process, but they are often forgotten after completion. We should be asking for these design models to be converted to as-builts, as well as creating a digital twin of the final building, including data on all systems and elements. These can be saved in the cloud to ensure information is always available and backed-up. This technology is already in use through Arup’s Neuron system, implemented on One Taikoo Place in Hong Kong.
Furthermore, hard stamping or using radio-frequency identification tags on structural components or equipment are quick and easy ways to link to specifications, material certificates or even directly into the 3D model. Harnessing and monitoring live data could prove incredibly powerful in supporting a change of load further down the line, increasing the flexibility of the building and justifying more efficient building codes of the future. These could even be used in foundations to explain reuse or in the stability structure to evaluate the building’s health after storms or earthquakes.
Looking ahead
Skyscrapers are engineering and architectural feats that reflect the power of human ingenuity. Now they have an additional purpose. In a post-pandemic world and in the age of climate change, skyscrapers showcase what future buildings must be: flexible, resilient and smart.
When designed and built correctly, tall buildings are vital to increase city density while facilitating a long-term and sustainable built environment. In contrast, poorly designed or executed tall buildings can undermine positive work in our cities. They can even be actively detrimental to our social wellbeing. It is therefore integral that we get tall buildings right, thereby bringing our sustainable cities of the future into being.
Words By Marc Easton – Senior Structural Engineer – Arup
Works Cited
Resch, E., & al, e. (2016). Impact of urban density and building height on energy use in cities. Build Green and Renovate Deep (pp. 1-15). Tallin and Helsinki: Elsevier.
