Image by Nicola Evans, WSP
Claudina Vaz is an undergraduate engineer currently enjoying a work placement at WSP. Roma Agrawal is an associate structural engineer at the firm, where she has worked for nine years on numerous projects including bridges, sculptures and the world famous Shard tower. She has won various awards, including the Institution’s "Young Structural Engineer of the Year" competition, and has been a Chartered Member since 2011. Here they explain some of the challenges structural engineers face when building super tall structures
A staggering statistic is that 70% of the world’s population will live in urban areas by 2050. It’s no wonder that an increasing number of super-tall buildings are being planned and constructed to cope with this demand. Skyscrapers allow space to be maximised in densely populated areas, minimise urban sprawl, reinvent the city skyline, and satisfy human fascination with tall buildings.
People’s affection towards tall towers varies hugely around the globe. In the Middle East living and working higher is a widespread aspiration, whereas in the UK it’s taken us longer to embrace super-talls. I am proud to have designed the spire and foundations for the world famous Shard, a building which is helping to stimulate the conversation about the place tall buildings will have in our future cities.
The science of tall building design is evolving rapidly to match increasing demand. As structures become higher and develop increasingly complicated geometry, structural engineers are challenged more and more to push the limits of what is possible.
Some of the main factors we have to consider are:
Engineers are constantly developing the way we use materials in the construction of tall buildings. Whether they are traditional materials like steel and concrete or newer ones like carbon fibre, we try to incorporate them in a way that makes the tall building both stronger and more efficient. Crucially lighter, stronger materials allow us to reduce the weight of the structure, minimise loads on foundations and ultimately make the building more economically viable.
Lift technology can be a limiting factor when we try to build taller. It is a problem because the steel cables used to suspend lifts are subjected to huge strain, mostly due to their own weight. Lifts can even be put out of service on particularly windy days, as they are easily affected by buildings swaying. This limits the maximum height of an elevator to approximately 500 metres, which is why tall buildings often have elevators that only go up to certain floors.
Human comfort and safety
Engineers have a lot to consider when ensuring that tall buildings are comfortable for the people living in them. Wind makes tall buildings sway – if the movement is too great, the building’s fabric might be damaged and if accelerations are too high, residents can experience a ‘sea-sick’ feeling.
There is also the vital question of safety. If there is a fire in the building we need to be certain that inhabitants can evacuate the structure quickly. The taller the building, the more vulnerable it is to these factors. Engineering solutions usually rely on suitably strong, stiff and robust stability systems for both the interior and exterior.
There are other considerations when building tall - we need to know more about the wind and air environment at different atmospheric levels and the effect of extreme temperatures. We also have to consider the practicalities of building at greater and greater height – how will construction crews of the future travel to and from the upper levels of a super tall building? Will they live at the top, rather like North Sea workers living for weeks on oil rigs?
We are faced with numerous challenges, but engineers are creating advanced techniques to overcome them. We work at the cutting edge of technology in order to enable humans’ aspirations for tall living.
It seems with the advancement of sophisticated computer modelling systems, materials and construction methods, the science of structural engineering will not impose a limit to how high we can build. It’s an exciting time to be a structural engineer.