When tremors shape the skyline26 July 2019
In both developed and developing economies, tragic events following large earthquakes have demonstrated that far too much of our building stock in seismic hazard zones is not fit for purpose. Fortunately, this is a fact that has been recognised in research labs, global legislative bodies and architecture schools, but to what extent can new techniques and approaches make a tangible difference? Ross Davies investigates.
In a presentation given in front of the Geological Society of America in September 2017, two of the world’s preeminent geoscientists warned of a potential spike in big earthquakes over the year ahead.
During their address, Roger Bilham of the University of Colorado, and Rebecca Bendick of the University of Montana, expounded the theory that fluctuations in the speed of the Earth’s rotation could bring about an upsurge in seismic activity.
Unfortunately, time would prove their predictions right. 2018 witnessed one earthquake measuring above 8.0 in magnitude, the same level as 2017, but there were 16 quakes between 7.0 and 8.0 in magnitude, a rise in 10 on the previous year. In total, there were 14,586 events measuring between 4.0 and 9.0 in magnitude, a year-on-year global increase of just under 2,000.
The deadliest to strike came on 25 February in Papua New Guinea, registering a magnitude of 7.5 and claiming the lives of 160 people. The biggest was the 8.2 quake in Fiji on 18 August. On that occasion, there were no fatalities.
Despite the significant rise in numbers, however, no quake came close to wreaking the disaster wielded on Mexico City in September 2017, in which a 7.1 earthquake tore through the Mexican capital, leaving a death toll of 230.
What subsequently transpired was that the main cause behind the fatalities was not the tremors themselves, but from collapsing buildings and flying objects. This is despite a number of new buildings springing up in Mexico City – and elsewhere – in recent years, comprised of new designs and materials, engineered to hold out during such seismic episodes.
The tragedy clearly indicated that many of these buildings still aren’t up to the task – and it is an issue that is not unique to Mexico. A recent assessment of high-rise buildings in Wellington and Auckland in New Zealand – both subjected to deadly quakes in recent years – showed many to be desperately lacking in their requirements to keep people safe during earthquakes.
Nonetheless, architects and engineers are talking of new frontiers of earthquake-resistant design. In Seattle, situated in the US Pacific north-west – an area infamously prone to quakes – work is currently taking place on one such building that is being billed as a game-changer.
Err on the side of caution
Rainier Square Tower, located in the heart of Seattle’s downtown area in the US, features a composite structural steel frame, in which cross-tied plates are filled with concrete to improve seismic resistance. With a rebar-free core, it could also be cheaper, easier and safer to build. Construction of the 850ft-tall building is set to reach completion later this year.
Yet Andrew Whittaker, a professor of civil engineering at the University of Buffalo, isn’t convinced the project merits as much excitement as it is being afforded in some design and engineering circles.
“We should be cautious with terms such as ‘game-changer’,” he says. “The composite construction being used for the tower in Seattle is the same form that contributed to the bankruptcy of Westinghouse Electric Company, which was associated with massive cost overruns at the sites of new-build nuclear power plants in Georgia and South Carolina in the US.”
“This form of construction is not yet proved to be a robust alternative to traditional reinforced concrete construction. I would wait until 10 buildings have been constructed using this form, and savings identified, before any talk of game-changers can be justified.”
But what of our building stock that’s already standing? Over at the University of British Colombia, a team of researchers is working to develop a new seismic-resistant, fibre-reinforced concrete that could one day be applied in earthquakeprone areas.
Known as eco-friendly ductile cementitious composite (EDCC), the retrofit technique works by spraying surfaces and walls with a thin layer of EDCC, which shares a similar molecular makeup to steel – in that it is strong, malleable and ductile.
Tests so far have produced positive results, claim the researchers, with EDCC shown to be able to withstand earthquake simulation tests with magnitudes as high as 9.1 on the Richter scale – the same level of intensity of the quake that devastated Japan’s Tohoku region in 2011.
“We sprayed a number of walls with a 10mm-thick layer of EDCC, which is sufficient to reinforce most interior walls against seismic shocks,” says Salman Soleimani- Dashtaki, a member of the research team. “Then we subjected them to Tohoku-level quakes, and other types and intensities of earthquakes – and we couldn’t break them.”
An issue beyond the remit of construction technique concerns the failure to undertake ongoing analysis of prone areas in more ‘stable’ periods. This is a particular problem in developing nations, especially within low-income communities where building codes may be out of date, non-existent or simply ignored. With rapid urbanisation adding to the problem, the financial and human costs in the event of a disaster are actually increasing in low and middle-income countries.
Developed nations, though, are in no way immune, due to an absence of robust frameworks for resilience testing. Even within moderate areas where a disaster may not result in loss of life, the damage costs alone are cause for concern, according to Iranianborn scientist and entrepreneur Farshad Mirshafiei.
During research for a PhD at McGill University in Montreal – which sits within the Western Quebec Seismic Zone – Mirshafiei identified gaps in the way in which buildings are seismically analysed.
The problem comes from the current method of assessment. At present, engineers carry out an assumption-based ‘finite-element model’ predicated on a building’s engineering plans, but they often lack the resources to sample the structural components sufficiently, and non-structural components are disregarded.
“The only way we can find the real response is if you have all the behaviour of connections, beams, columns, structural, non-structural components and their interactions,” Mirshafiei says. “If you can model it perfectly, you can find the response, but no one can do it. The final result is based on how much time they want to invest, how much they want to go into detail in the modelling, and it’s not robust. You need to have a robust methodology so that everybody is going to get the same results.”
Mirshafiei’s solution, his programme Sensequake, is an analysis platform that allows a structure’s baseline to be read using sensors placed around the building. An advanced algorithm then allows the earthquake risk to be calculated. Eventually, Mirshafiei hopes to extend the technology to assess resilience to other forces such as hurricanes.
However, even with such a methodology widely adopted, a second problem remains in the apparent unwillingness of governments to assess and reinforce the built environment on a regular basis. While recent builds are constructed according to safer modern building codes, a huge number of older structures remain in use. Analysing and strengthening these buildings is vital, Mirshafiei emphasises.
“Even if governments don’t have the budget to do it for all existing structures, they need to do it for critical post-disaster buildings like hospitals, schools, fire stations, police stations and shelters, because you never know when an earthquake is going to happen,” he says.
Unfortunately, the short-term expense of reinforcement is often off-putting. Take Los Angeles (LA), in the US, where a law obligating the retrofitting of over 15,000 seismically vulnerable apartment buildings was finally introduced in October 2015, after years of delay. The significant costs of this reinforcement – in the millions for some buildings – currently fall not to the government but to private owners.
Call to mind the enormous damage costs in the event of a disaster, though, and resilience is an easy case to make. LA’s Northridge earthquake in 1994 cost $25 billion in damage. Worldwide, the average annual losses from natural disasters are now estimated at $314 billion in the built environment alone.
Shakes to stay standing
As one of the world’s most earthquake-prone countries, Japan has long sought to come up with innovative ways to stand tall during seismic events. High-rise buildings in Tokyo commonly make use of absorbing devices – known as isolators – in their foundations, made from the likes of laminated rubber, which prevent ground movement from reaching the building.
Could new technologies be afoot? NTT Facilities, a subsidiary of the Japanese telecoms giant, is reported to have developed the world’s first artificial intelligence-based system able to stop quakes in their tracks.
Able to analyse the movements of buildings, the AI works by shaking in step with tremors, in effect cancelling them out. According to Japanese media reports, the technology will be made available in the country’s Kansai region in the near future.
Whittaker, however, argues that the system is not as a novel as reports are making it out to be. “The AI-based system is not new,” he says. “30 years ago it was described as ‘active control’, and implemented to mitigate earthquake effects on a tower in China.
“There is a mischaracterisation here of seismic isolation, which is now a mature earthquake-resisting technology that has been applied to buildings, bridges and missioncritical infrastructure, in North and South America, Europe, Asia and New Zealand.
“Seismic isolation, coupled with damping devices in some circumstances, is likely the best available option for low and mediumrise buildings that have very high standards for seismic performance.”
Decades of international agreements have so far scratched the surface of risk reduction, but a raft of promises stemming from global summits – including the UN World Conference – have placed resilience centre stage. Much of the impetus must remain at state-level, but, as commissioned craftsmen of our built environments, architects too must carve out a proactive role in prevention and cure.
For Shigeru Ban, whose humanitarian work in post-quake sites played a huge role in the 2014 decision to award him with the Pritzker Prize, it is for individual architects to decide their own intentions in this regard, but he does detect positive signs for the future.“I do not intend to force my philosophy on others,” he says. “However, when I have lectures in various places, I can see that people – such as young architects – are becoming more interested in helping victims of natural disasters, and I feel the idea is spreading.”