Tuesday, 4 February 2014

Advanced Earthquake Engineering and Preparation in Japan

Japan is a nation that has grown rapidly in the last few decades, both economically and socially. During its development Japan invested well in technology and is now one of the biggest technology exporting countries in the world today. Moreover it has managed to achieve this despite being in an area of the world that is riddled with environmental hazards. 

One of the most hazardous is the threat of a major earthquake. Tokyo, is one of the three most densely populated cities on the planet where seismologists expect major earthquakes to occur. However it is one of the few places on the planet where such seismic activity doesn’t usually cause catastrophic damage. Why is this? It is because of the adaptation techniques that Japan have installed.

Adaptation is the process by which a country prepares itself for the inevitable hazard, in this case earthquakes and their side effects. One way in which Japan has done this is by changing the way in which modern buildings are designed. It is possible these days the design buildings to sustain the effects of the ground shaking caused by earthquakes because we now know far more about how buildings behave in different scenarios.  

One way in which buildings are being designed to sustain the effects of an earthquake is by putting in dampeners. This is far cheaper to do than using building techniques that make the structure far stronger. A dampener is a mechanism that absorbs the energy of the vibrations caused by the quake and makes the movement die away over time. 

One type of dampener is  called a tuned mass damper (TMD). This involves installing a huge mass, either mounted on springs or as a pendulum, which is tuned to have a natural frequency close to that of the building. In the event of an earthquake at close to that resonant frequency, the TMD oscillates in the opposite direction to the building, counteracting its motion. 

The natural frequency of the building can be calculated by using the formula:

where K is the stiffness constant of the building and M is the mass of the building.  Structures can be both reinforced horizontally and vertically, by using: diaphragms, trussing, braced frames, shear walls and moment resisting frames.

However structural reinforcing and engineering is not the only way in which Japan is reducing the damaged caused by earthquakes. They have installed my pre-earthquake warning systems such as sirens that allow people such as school children to prepare for the imminent tremors by doing things such as hiding under desks or gathering in areas that should be safest from falling debris and collapsing buildings. 

Another way in which Japan try and prevent catastrophes during earthquakes is by shutting down core reactors in nuclear power plants to avoid meltdowns and radiation related disasters. 

The way in which Japan is now prepared for the threat of earthquakes has not always been the case and much of the planning and building regulations for “earthquake safe” buildings only came in after the Kobe earthquake in 1995. During which over 6,400 people lost their lives and thousands of homes were destroyed.

Sam Evatt

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