Like puzzle pieces, Earth’s outermost layer is composed of tectonic plates that shift and collide against one another, accumulating stress over time. As the friction is overcome, an accumulation of seismic energy is suddenly released in the form of an earthquake (Kukowski, 2016). But while natural quakes destroy buildings, how have engineers worked to create better preventative solutions? An intriguing method to combat earthquakes is to build earthquake-resistant infrastructure. This can take the form of highly developed designs, often reinforced against seismic activity and with increased overall resistance.
One of the most traditional methods to build earthquake-resistant structures focuses on achieving a ductile design. The ductility of a building measures the materials within that building by their ability to withstand large strains. The most important factor is that the building can dissipate seismic energy without breaking. On the scale of ductility, bricks and concrete are very low, while structural steel is one of the most ductile materials (Newton, 2021). Diving deeper, you may wonder what techniques are used to build earthquake-resistant structures. Since the 1980s, a method known as seismic base isolation has been applied to buildings (Nakamura and Okada, 2019). The main premise of this technique involves installing isolation devices and energy-absorbing devices underneath buildings. As seen in Figure 1, common types of isolation devices are laminated rubber bearings, which are made with layers of rubber and steel wrapped around a solid lead core (Nakamura and Okada, 2019). Coupled together, the bearings help dissipate energy caused by seismic movement. As research is further improved, seismic base isolation is quickly proving to be an excellent modern tactic of earthquake prevention.
Figure 1: A laminated rubber bearing with a lead core (Ju, Yuantien and Hsieh, 2020). The lead core bears the heavy load of the structure and provides hysteretic energy dissipation (Sahoo and Parhi, 2018), while the layers of rubber and metal constrain the lead core and help recover the bearing to its original position.
In particular, Japan has invested heavily in the development of seismically isolated buildings. The country has a history of devastating earthquakes, such as the Great Hanshin earthquake in 1995 and the Great East Japan Earthquake in 2011. After such significant events, the number of buildings created with this design has drastically increased. Figure 2 below shows the number of seismic base-isolated buildings according to a survey completed by the Japan Society of Seismic Isolation (Nakamura and Okada, 2019).
Figure 2: Number of buildings with seismically isolated base designs in Japan (Japan Society of Seismic Isolation, 1982-2015). The colour-coded bars represent the number of buildings with specific functions. Looking at the subsequent years after 1995 and 2011, there are spikes in the graph. This data corresponds with Japan taking action to build earthquake-resistant structures after two major earthquakes.
The Tokyo Skytree stands as a result of Japan’s ingenious engineering techniques. At a height of 634 metres, the building has a unique design, incorporating similar technology as isolation devices. A special installation of central steel-reinforced concrete columns connects to a damping system known as a tuned mass damper (Holloway, 2012). This central-pillar technique is called “Shinbashira” and can date back to 594 AD when the world’s oldest wooden structure was built (Gowan, 2021). Together, the technology works to move with a time lag to reduce vibrations and to keep the centre of gravity (Katanuma, 2021).
Due to the unpredictable nature of earthquakes, research on seismic-resistant structures will always be ongoing. But with each quake, engineers and scientists learn more about how well our modern technology stands up against nature. So what is the next step? How can we design similar techniques to be applied in developing countries? Keep in mind that many do not have resources for the same type of investment as Japan. What methods can be more cost-effective but provide a similar level of resistance?
Reference List
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