Between 1994 and 2013, roughly half a million people around the globe died due to earthquakes while over 118 million (approximately) were affected. The situation may get more life-threatening in the coming years. According to the Centre for Research on the Epidemiology of Disasters (CRED), as more people are moving to highly seismic zones in the urban areas, it is adding to the number of crowded and poorly constructed settlements that are extremely likely to be unsafe during an earthquake.
In light of the fact, it is cities that are most prone to the impact of quakes, particularly the ones that have been the most innovative. The aftermath of the earthquakes in cities shows that most of the casualties are caused due to the collapsing of buildings, and not the natural disaster itself.
Hence, to cope up with the challenge, in 2015, the UN general assembly approved a 15-year voluntary agreement to reduce the probability and impact of such disasters around the world. Known as ‘Sendai Framework for Disaster Risk Reduction 2015-2030’, the agreement aims to curb the human and economic costs of natural calamities and enhance global cooperation. It focuses on building better from scratch by adopting appropriate design and construction strategies while also retrofitting and restoring the existing structures. These focal points among others are supporting nearly 100 countries worldwide.
Few of the smart cities (as we call them) from different parts of the world have been striving to become more resilient and resistant to earthquakes, that are way more devastating than floods. These stories reveal strategic solutions that are instigating. Read on to spur the change!
Constructing Earthquake-resistant Buildings
Christchurch
After the disastrous earthquake in February 2011 that caused 185 deaths and substantial loss in Christchurch, the city reacted aggressively. It was found that the multi-storey steel structures including eccentrically braced frames (EBFs), concentrically braced frames (CBFs) and resisting frames (MRFs) reopened shortly after the quake. In fact, modern light steel-framed houses from 1-3 storeys suffered no to very little damage even in the strongly shaken regions.
Detailed studies conducted in New Zealand and the USA revealed the absence of significant damage in these steel structures was due to the high strength/stiffness ratio of steel, soil-structure effects, and buildings holding extra stiffness/strength than that considered explicitly in design. The extra strength was a result of concrete slab effects and presence of non-structural elements like interior walls and cladding.
Advantage of steel structures comes with the fact that they reinforce buildings and don’t need to remove walls to assess any damage. Pacific Tower, 23-storey building, the tallest in the city survived the quake with just one steel link falling. It was evident that steel structures outperformed concrete buildings.
Mexico City
A similar instance was seen in Mexico City earthquake on 19 September 2017. The buildings that collapsed used cheap flat-slab concrete construction that has now been banned by many countries. Torre Mayor, the 57-storey office building in the same city was built using proper materials and technologies. The building sitting on a foundation backed by 252 deep-drilled piles which fasten a superstructure of reinforced-concrete-encased steel columns and structural steel, did not sustain any visible damage during the disaster. 98 seismic dampers incorporated in it absorb and neutralise the earthquake vibrations.
Istanbul
Istanbul is an earthquake-prone city. So, when construction for a second international airport was approved, seismic resistance was one of the top priorities. Today, the Sabiha Gökçen International Airport uses “base isolation” to reduce the impact of earthquakes. Base isolation is a technique in which a building stands on pads or bearings that separate the structure from the encircling earth. This means that it tremors less during a quake and sustains minimal damage.
Arup, the airport’s engineering designer, incorporated 300 isolators that lessen the lateral load of an earthquake by 80%. Theoretically, this indicates that the structure can survive a quake of 7.5-8 on the Richter scale. The airport is one of the biggest seismically isolated constructions in the world.
Sensor Technology To Improve Resilience
Southern California is going to have a new optical sensor that accelerates the reopening of critical buildings after a major earthquake. After two recent shakings experienced in the city, seismologists have warned of more such happenings in the future.
The new technology to improve resiliency was developed at Lawrence Berkeley National Laboratory. It autonomously gathers and transmits data related to inter-storey drift. As per researchers, it will provide reliable information about any building damage to speed up efforts to repair and reopen buildings post-quake. This will be critical especially to reoccupy hospitals as soon as possible.
It will help building inspectors understand a building’s drift profile enabling them to inspect the most at-risk buildings first. As a result, this will save a significant amount of time compared to manual inspections that take days to let people reoccupy a building.
The work on the new technology began in 2015, the research was reviewed by peers and simulation testing was executed at the University of Nevada Earthquake Engineering Laboratory. And now, the Discrete Diode Position Sensor (DDPS) will be installed for the first time this year in a multi-storey building at Berkeley Lab, that sits near Hayward Fault, believed to be one of the most dangerous faults in the US.
Until now frequency limitations of sensors and the inability to receive data quickly to accelerate decision-making was a challenge. However, DDPS comes as a hopeful solution that combines laser beams with optical sensors. The roll-out of 5G will further support the required data transmission speed.
The September 2017 earthquake that shook Mexico lead to a school becoming the first in the city to be equipped with a cheap sensor system to monitor quake and assess any damage if occurred.
The kids of Mariano Matamoros Elementary School still get frightened over a noise that feels like an earthquake has come.
Pulse, as the sensor technology is called was supplied by company Grillo, is not new. Earthquake engineers have used these in skyscrapers and bridges to look for hidden damage that may be deadly. For instance, 50 minutes after the shaking stopped in Mexico, some people got back to work in a four-storey building, which later collapsed.
According to the researchers at Grillo, the Pulse sensors installed on each floor of a building helps measure how many floors have moved out of alignment during a quake.
Although Pulse does not replace expert inspections, it does serve as a tool that experts can use to enhance their action after a strong shaking.
The rapid response of people of Anchorage, the largest city in Alaska shows that there is more we can do to recover quickly after an earthquake. When recently in 2018, a quake of 7.0 magnitude hit the city, some roads broke apart severely. But just a week after, the roads were reopened, as a result of the crew working 24/7 to repair the damage.
The region has experienced more quakes than any other place in Alaska, and people take this very seriously. The quick fix achieved by the city indicates how time and money can be invested into adaptations of these kinds, even when there is no clue where or when a quake may occur.
