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Why are Japanese houses so earthquake-resistant?
2019-06-24

Japanese architecture is also particularly particular about the selection of materials, such as bricks and tiles, which are often used as the main building materials in Europe and China, and can hardly be found in Japanese architecture now.


Brick structures are almost no longer used in Japan, but are replaced by reinforced concrete structures supplemented by light wall materials. This kind of structure is not only safe and earthquake-resistant, but also energy-saving.


The 55-story, 185-meter-high Kawaguchi Apartment in Saitama County, Japan's tallest apartment building, uses 168 CFT steel tubes, the same building material as the World Trade Center in New York, USA. The diameter and thickness of the steel tube are up to 800 mm and 40 mm respectively. Special concrete is injected into the core of the steel tube, which is three times stronger than ordinary concrete.

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1. There are almost no brick houses, replaced by light wall materials.


In Japan, an earthquake-prone country, the seismic standards of buildings are strictly stipulated by the Building Standard Law and the Enforcement Ordinance of the Building Standard Law. The Building Standard Law stipulates that new buildings must achieve the aseismic strength not to collapse in a once-in-a-century earthquake and not to be damaged in a once-in-decades earthquake. Only buildings designed to comply with the law are allowed to be built.


According to this law, building materials must be officially certified, and unqualified building materials are difficult to circulate in the market. At present, Japan's buildings are basically divided into three categories in terms of seismic resistance: one is seismic structure, the other is seismic structure, and the third is aseismic structure.


The so-called seismic structure, the most important principle is to improve the strength and toughness of columns and walls, the building as a whole can withstand vibration. At present, this method is mainly used in our country. Both aseismic structures and seismic structures are relatively new technologies.


In Japan, the cost of replacing aseismic structures with aseismic ones only needs to increase by 5%-10%.


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Japanese architecture is also particularly particular about the selection of materials, such as bricks and tiles, which are often used as the main building materials in Europe and China, and can hardly be found in Japanese architecture now.


Brick structures are almost no longer used in Japan, but are replaced by reinforced concrete structures supplemented by light wall materials. This kind of structure is not only safe and earthquake-resistant, but also energy-saving.


The 55-story, 185-meter-high Kawaguchi Apartment in Saitama County, Japan's tallest apartment building, uses 168 CFT steel tubes, the same building material as the World Trade Center in New York, USA. The diameter and thickness of the steel tube are up to 800 mm and 40 mm respectively. Special concrete is injected into the core of the steel tube, which is three times stronger than ordinary concrete.


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In the northeastern part of Japan, where it often snows in winter, in order to cope with the snow, most of the local people use iron roofs when building houses.


Wang Weizeng, a registered structural engineer at the China Academy of Architecture, wrote: "The quality of a building with iron slabs as its roof is much lighter than that of a building with tiles. In addition, in order to keep out the cold, the opening of doors and windows of the houses in this area is smaller, which makes the rooms more seismic. Less houses collapsed, greatly reducing casualties.


The common characteristics of new materials commonly used in Japanese housing construction are light weight and high strength, such as resin, aerated concrete and carbon fibers. Even if they collapse and fall, they will not cause serious harm to human body. Moreover, they are easy to install and build as easily as building blocks.


2. Ground and Seismic Isolation


In 1996, Japan implemented the "Seismic Rehabilitation Program" and widely used the isolation technology. The isolation layer was added between the building and the foundation to absorb the seismic energy by the shaking of the building itself.


This technology is to install elastic rubber pads at the bottom of the building, or friction sliding bearing buffer devices to resist earthquakes.


These rubber layers are very durable and generally have a service life of about 60 years. They can reduce the shaking of buildings by 1/3 to 1/5.


There are many tall buildings in narrow and crowded Japan. In order to withstand the damage caused by earthquakes, this kind of foundation seismic isolation technology is widely used in high-rise buildings in Japan.

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For example, a 93-metre aseismic apartment built by a company in the Tokyo metropolitan area of Sugiyama uses high-strength 16-storey rubber on the periphery of the building and natural rubber system on the central part of the building.


When an earthquake of magnitude 6 or above occurs, this kind of protection device can reduce the stress of a building by half.


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After the implementation of this technology, the cost of housing will be increased, the cost of general buildings will be increased by 10%, and the cost of apartment buildings will be increased by 25%.


3. Box design


In order to improve the seismic capacity of traditional wooden structures, ordinary Japanese houses adopt box design, which can ensure that when an earthquake occurs, the houses will not disperse, even in severe shaking, they can roll over as a whole and not be damaged.


When the earthquake in eastern Japan triggered a tsunami in March 2011, television pictures showed many houses washed away without being shaken.


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Of course, professional and technical personnel will regularly assess the seismic reinforcement grade of civil housing, and the government will give residents appropriate subsidies and incentives as appropriate.


The history of the development of earthquake-resistant buildings is the history of the continuous improvement of the building law. "After every major earthquake in Japan, the Ministry of Land and Transport will organize forces to carry out the building seismic investigation, and according to the results of the investigation, put forward suggestions for the revision of the Building Standard Law." During the 2010 Shanghai World Expo, Japanese Industrial Pavilion building producer Yukio Isaki has publicly stated that Japanese architects will strictly comply with the seismic requirements of the "Building Standard Law" when designing buildings.  And the law is revised every few years.


Looking back on the history of Japan's earthquake-resistant building development is the history of its building laws and regulations constantly improving and developing.


In the latter half of the nineteenth century, Japan had just begun to study earthquakes. At that time, Japan had not proposed that buildings should have seismic fortification capability. In 1892, the "Earthquake Prevention Investigation Society" was established. Their goal is to improve the seismic resistance of wooden buildings.


Since then, the study of earthquake resistance in Japanese architecture has entered a stage guided by a scientific world outlook. In 1916, Japanese architect Sayono Riichi put forward the "Static Seismology Method", suggesting that the horizontal force should be 1/15 of the weight of the structure in the structural design, so that it can play an anti-seismic role.


In 1923, the Societe Generale Bank Building was built according to this design idea. In September of the same year, the Great Kanto Earthquake happened, and the Industrial Bank Building withstood the test. Thus, the principle of "static seismic method" became the norm of seismic design in Japan's urban building law implemented in the second year. Since then, Japanese buildings have entered the 1.0 era of earthquake resistance and disaster reduction.


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In 1968, more than 100 meters high Xiaguan Building was built. At that time, the building used prefabricated reinforced concrete energy-dissipating shear walls and steel frame structures. It sounds a little difficult. You must have heard the term "load-bearing wall" in decoration. It is mainly used to bear vertical load, while "shear wall" is used to support horizontal load. Simply put, the idea at that time was to use Strnger's materials to build Strnger's tall buildings so that they could withstand strong winds and earthquakes.


Since 1924, Japan's building codes stipulate that seismic coefficients should be taken into account in the calculation of structural forces. In this respect, Japan was at the forefront of the world at that time.