Hundreds of millions of people living and working in cities around the world are at risk from the unpredictable and potentially devastating effects of earthquakes. The ongoing challenge for property developers, architects and engineers looking to construct new buildings in affected regions is how to balance architectural ambition with safety and cost concerns.
While it may never be possible to accurately predict when and where an earthquake will hit, advances in seismology combined with cutting-edge computer software and engineering technologies offer solutions that mean it is possible to minimise risk by building intelligently.
There are several steps that can be taken to improve a building’s ability to withstand the sort of horizontal acceleration that occurs during an earthquake. Michael Willford, Global Seismic Design Leader at architectural consultants, Arup, explains that innovative engineering products can help to prevent collapse and even limit damage so buildings remain safe for occupation after a quake.
“Lower damage levels can be achieved by modern technologies such as seismic isolation, supplemental energy dissipation devices, and structural systems that accommodate rocking rather than yielding.” These systems include seismic isolators – large bearings that sit between a building and its foundations and that move side-to-side during an earthquake, absorbing the majority of the energy and limiting the impact of uneven forces on the structure.
Arup applied this method to the construction of the world’s largest seismically isolated building, the international terminal at Sahiba Gökçen International Airport in Istanbul, Turkey. The building covers over 40,000m2 and sits on top of more than 300 isolators that reduce lateral earthquake loads by 80 per cent.
Architects looking to ensure optimum structural performance in buildings that may be exposed to earthquakes are encouraged to focus on balanced symmetrical forms that reduce the likelihood of torsion or twisting. For example, the Y-shaped plan of the world’s tallest building, Burj Khalifa, provides stability and distributes loads and stresses evenly throughout the structure so there are no weak points.
Innovations in computer simulation software offer a vital tool for architects wishing to employ more expressive shapes, enabling them to identify possible weak points in the design. Michael Willford worked on the unusual looping structure of the CCTV Headquarters building in Beijing, which was completed last year, and says that the building’s top-heavy form required detailed analysis prior to construction. “The design was checked for seismic performance by means of 3D non-linear seismic response simulation for numerous potential earthquake shaking records,” he explains. “This enabled the strength of the many braces to be optimised, and the potential damage in the largest credible earthquakes to be minimised.”
In cities that regularly experience earthquakes, such as Beijing, Tokyo and San Francisco, architects and engineers are required to ensure their buildings meet the highest grades of seismic resilience. In other regions, where earthquakes are less likely, it is possible to reduce expenditure in this area while still achieving suitable safety levels. Due to the city’s high concentration of skyscrapers, the Dubai Municipality treats earthquake resistance very seriously.
Dubai is sited on seismically stable ground, with the nearest fault line, the Zagros Fault, approximately 200km away. Despite this, new buildings over four stories high must adhere to the international Uniform Building Code 97 (UBC) and are designed to meet seismic zoning standards far above what is required in a region that is unlikely to ever experience significant tremors. By implementing this ‘safety-first’ approach, Dubai is able to ensure that some of the world’s most ambitious buildings are built to withstand anything the Earth is likely to throw at them.
The latest technological and engineering innovations mean it is feasible that even the tallest skyscrapers could be built to be virtually earthquake-proof; however, in most scenarios this is unnecessary and prohibitively expensive. Michael Willford recommends that developers adopt a “performance-based approach” to the design of tall buildings that uses simulation software to evaluate risk and “permits any type of structure to be adopted, provided analysis shows that its performance will meet the intended objectives.”
This system is already in place in high risk regions including China and Japan, but its global implementation could improve safety standards, cost efficiency and creative possibilities across the construction industry.