From the underground, up. Engineering our future cites

Over the last 100 years cities have changed beyond recognition. Roma Agrawal structural engineer, and part of the team who designed the Shard, reveals how building design today is shaping what cities will become tomorrow

In 1800, 3% of the world’s population lived in urban areas, by 1950 this had increased to 30%. In the last few years, for the very first time in recorded history, the majority of us live in cities. By 2030, the world is projected to have 41 mega-cities with 10 million inhabitants or more.

As a structural engineer, I design buildings and bridges and am responsible for ensuring the safety and comfort of the people that live and work in them. But a successful structure is one that works for its users and makes sense in the landscape of 2050 just as much as 2016.

Whereas now, we are used to a bird’s eye (or google maps) views of our city showing clear outlines of buildings intersected by ribbons of train lines and roads, I believe the future city will be far more complex and challenging to map. We will increasingly think of our cities as three dimensional, less like a flat pancake and more like a multi-tiered cake. I see us moving roads and services further down underground, creating more space at ground level for parks and pedestrianised squares. Buildings will get taller, and increasingly incorporate activities at higher levels we currently see mostly at ground level e.g. shops, restaurants, car parks. We may see multiple layers of transport / connectivity corridors weaving between and even through our future buildings.

And some of this has already begun. In the last few years, I have worked on three projects in central London which entail creating space where we previously thought there was none – over and around pre-existing rail tracks and tunnels. This model brings its challenges – trains shake everything around them as they thunder past. There is even the risk that a derailment could generate a collision with the structure above, and threaten people’s safety.

To stop someone’s tea from rattling when a train runs past, we have learned how to ‘isolate’ the skeleton of a building from the ground. Large, robust rubber pads sitting between the foundations and columns act as a buffer, absorbing the vibrations and minimising the amount of force that travels into the building from movement of trains underneath. It sounds counter-intuitive to use a material like rubber to separate large pieces of steel or concrete, but this is proven method and it works.

In designing buildings that sail above train tracks, we are becoming savvy with scenarios. If a train derails and hits a column, we make sure that the building stands strong even with a column missing – by giving the loads somewhere else to travel through its skeleton. Computing power allows us to test multiple permutations of impact and create a resilient structure with in-built redundancies. And as materials become stronger, trains lighter, and computer software ever smarter, I can see this evolving until not just train lines but stations become fully integrated within high-rise towers at different levels of our layered cities.

Clever engineering and construction techniques have also allowed us to respect our past as we race ahead with our future. Cities like London have hundreds of centuries-old buildings which give them character and continuity. In many cases, the buildings are no longer fit for purpose, with safety concerns such as tight headroom, poor insulation and no lifts. We can preserve the essence of these buildings by ripping out the skeleton but keeping their skin intact. London has many such examples of old distinguished buildings, with spacious atriums, modern glass interior courtyards and efficient technology driven heat and lift systems.

Britain’s unique combination of architectural heritage and modern technology means we can use exciting engineering to allow our cities to be preserved and evolve. By modernising the old, and creating more intricate layers, we can accommodate growing urban populations. Alongside our rapid advances in technology we need our planning laws, transport policy and zoning regulations to evolve to a new reality. Where engineering leads, government will need to keep up.

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