Cracking the code on earthquakes
EXPERTS EXPLORE EVERY OPTION FROM STRUCTURAL PROPS TO SUPERMATERIALS TO LIMIT DAMAGE FROM SEISMIC EVENTS
Experts explore every option from structural props to supermaterials to limit damage as global death toll due to quakes between 1994 and 2013 stands at 500,000 |
Earthquakes affect every continent, though certain areas — the Pacific border of South America, the western coast of North America and Mexico, Alaska, south-eastern Europe, New Zealand and much of Asia — are especially prone.
Though rarer than floods, they can cause devastating damage and large numbers of casualties very quickly. The Haitian earthquake in January 2010 killed an estimated 230,000 people, injured 300,000 and displaced 1.5 million from their homes. It also caused around $8 billion (Dh29.37 billion) of destruction.
These figures may get worse. According to the Centre for Research on the Epidemiology of Disasters (CRED), more people worldwide are moving into urban areas in highly seismic zones, contributing to the number and size of squats and slums that are extremely vulnerable in the event of an earthquake.
The global death toll due to earthquakes between 1994 and 2013 stands at nearly 500,000, with a total of 118.3 million people affected.
It is collapsing buildings that cause the most casualties, not the earthquake itself — meaning harm-reduction measures can make an impact.
In 2015, the UN General Assembly endorsed a 15-year voluntary agreement to reduce the likelihood and impact of disasters around the world. Named after the Japanese city where it was endorsed, the Sendai Framework for Disaster Risk Reduction 20152030 aims to lower the human and economic costs of natural catastrophes and improve international cooperation.
Nearly 100 countries have Sendai Framework focal points, with four priorities for action. Priority three — “Investing in disaster risk reduction for resilience” — covers “building better from the start” using proper design and construction, as well as retrofitting and rebuilding existing structures. But where to begin? Not surprisingly, it is the cities most prone to quakes that have been the most innovative.
Nearly 31,300 earthquakes were felt in New Zealand last year alone, and one of the most prone areas is the capital, Wellington. Earthquake preparedness has been a high priority since the devastating Canterbury earthquake in February 2011, which caused 185 deaths and significant damage in the city of Christchurch. The city has since responded aggressively.
“When strengthening a building for earthquakes, the approach is to retain the existing structure to take vertical gravity loads, and add structure or reinforce existing structure to take the lateral — sideways — loads from earthquakes,” says Dr Geoff Thomas from Victoria University of Wellington.
A popular means of reinforcing a building is to add a steel structure. The most common type is the eccentrically braced steel frame. EBFs, as they’re known in the industry, are stiff themselves, and so suit stiff concrete or unreinforced masonry walls. Often they’re added to the exterior of a building, as it is cheaper and easier than adding to the interior —although this does alter the structure’s appearance.
The effectiveness of EBFs were tested in the series of earthquakes that shook Christchurch in 201011, and it was found by researchers to be “generally better than expected”. The 23-storey Pacific Tower, the tallest building in the city, survived the earthquakes with only one steel link failing.
Another advantage of fitting steel frames is the ease with which they can be examined after a quake: you don’t need to remove walls to assess any damage.
When structural steel is often left exposed as a focal point, it could even be factored into buildings’ designs. In an article in Modern Steel Construction in 2014, architect Terri Meyer Boake called on her colleagues to embrace the opportunity to modify structural steel to help improve earthquake resilience — both in new builds and when retrofitting existing buildings. “This holds promise for seismic reinforcing systems,” she wrote.
Composite material
In the 20 years up to 2013, Japan reported the world’s second biggest economic losses from natural disasters — nearly $500 billion. The majority was due to earthquakes.
One building on Honshu, Japan’s biggest island, has been shrouded in a new kind of material in an attempt to help it withstand future tremors. The building, known as Fa-bo, is owned by Japanese textile company Komatsu Seiren. It’s made of reinforced concrete and has been retrofitted with Cabkoma strand rods, developed by the company. These rods are 9mm wide, a composite of thermoplastic and carbon fibre, and five times lighter than metal of the same strength.
In a design by architect Kengo Kuma, Cabkoma rods were attached from the roof of the building to the ground, wrapping it in a light curtain. The rods are also used in partition walls inside. The idea is to help the building move during a quake.
As cities become more crowded, slums and squats grow, spreading on to surrounding slopes and embankments. These areas are particularly prone to damage from landslides after quakes.
“Many other recurrent and pressing needs tend to put seismic vulnerability on the back burner for governments and homeowners,” says Juan Caballero of Build Change, a nonprofit social enterprise that aims to save lives in hurricanes and earthquakes. “An earthquake is a very intangible risk until it happens,” he says.
Build Change launched its Latin American programme in 2012, working with municipal governments to retrofit vulnerable housing in Bogota and Medellin. With partners and local professionals, it developed a manual that helps people evaluate and retrofit low-rise vulnerable houses, to improve their ability to withstand earthquakes. The pilot programme involves 50 houses in each city, eventually scaling up to 500 per year.
The organisation gives decision-making power to the homeowners, and the improvements they suggest use existing, familiar techniques. “We try to present at least a couple of options to the homeowner, so that they can decide,” says Caballero.
Bamboo has been used as a cheap, sustainable building material for centuries, including in Asia and Central and South America.
In April 2016, an earthquake claimed hundreds of lives and 35,000 homes on the northern coast of Ecuador. Architects Al Borde say that a school they built using bamboo in 2009, Nueva Esperanza, responded well to the quake.
Housing prototypes
The architects have also found an interesting way to reuse materials from Habitat III, the UN conference on housing and sustainable urban development, which took place in Quito in October 2016. One of the structures from the exhibition is now being used to develop housing prototypes for rural Ecuador, which would, according to the architects, “allow a cheaper and faster construction with a smaller carbon footprint”.
Professor Saiid Saiidi at the University of Nevada, Reno, has worked in earthquake engineering for over 35 years. Much of his work focuses on bridges.
These essential pieces of infrastructure can be built faster when parts are prefabricated — but can bridges manufactured in this way resist earthquakes as effectively as conventional ones?
To find out, Professor Saiidi’s team has been developing earthquake-resistant bridge connections for premade elements. They’ve been testing three 22-metre-long bridge models in the lab on shake tables, which simulate an earthquake of approximately 7.5-8 magnitude.
Another area of research is bridge columns that use metal alloys with “shape memory”.
The World Health Organisation has published guidance about hospital construction to ensure they survive earthquakes as well as possible, and seismic isolation has also been incorporated into new hospitals.
Earthquakes killed 20,000 people in Turkey in the past 18 years, and Victor Zayas, an engineer and founder of the California-based Earthquake Protection Systems, says half of these live could have been saved if hospitals had remained functional.
Architects have also found an interesting way to reuse materials from Habitat III, the UN conference on housing and sustainable urban development, which took place in Quito in October in 2016.