Seismic performance of buildings in Japan

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(Updated on December 27, 2016)

Japan is widely known around the world for its earthquakes, but many people are amazed when they realize that the world’s oldest wooden building Horyuji (Horyu Temple) has survived multiple massive earthquakes. The temple shows that Japan had highly advanced construction technologies even in the ancient times. The Japanese construction technologies have made continuous improvements to increase safety during earthquakes, and have now become the most advanced in the world. In 1924, Japan introduced the world’s first earthquake resistance standards for buildings, and subsequently, the standards have been revised to become stricter each time when a massive earthquake occurred. When purchasing a real estate property in Japan, it is important to know about the earthquake resistance standards and construction technologies. We therefore recommend you to check each of the following points for analyzing a building’s seismic performance.

 

 

Does the building meet the new earthquake resistance standard requirements (when was the building constructed)?

Earthquake resistance standards

The earthquake resistance standards are technical standards for structures that are necessary for a building to be safe during an earthquake. The standards are set forth in the Building Standards Act, Order for Enforcement of the Building Standards Act, and Notification of the Ministry of Construction. The old earthquake resistance standard is that used from 1950, when the Building Standards Act was established, until May 31, 1981 for the verification of constructions. This old standard was established as a structure standard where applicable buildings should not collapse in earthquakes of seismic intensity of upper 5, and even if the buildings suffered damages, they could be lived in again after repair. This standard was later significantly revised after the 1978 Miyagi Earthquake, and from June 1, 1981, the new earthquake resistance standard was enforced. In this standard, the frames of the buildings should not be damaged in earthquakes of seismic intensity of upper 5, which are said to occur once in several decades, and buildings should not collapse in earthquakes of seismic intensity of upper 6 to 7, which are said to occur once in several hundred years. Subsequently, the Building Standards Act has been revised numerous times, including the significant revision enforced on June 1, 2000 triggered by the Great Hanshin Earthquake in 1995, and the revision enforced on June 1, 2005 after the 2004 Chuetsu Earthquake. As such, the construction date of the building will be one of the factors for judging the building’s seismic performance. Buildings constructed in or after 1981 (buildings for which applications were made for building verification on or after June 1, 1981 to be precise) should meet the new earthquake resistance standard, and can be considered to have a certain level of seismic performance. The buildings constructed in or after 2000 (buildings for which applications were made for building verification on or after June 1, 2000) should have more improved seismic performance. There also exists an “earthquake resistance standard certification of compliance,” which is a certificate certifying the building’s conformity with the new earthquake resistance standard. This is a certificate issued by an architect who belongs to a registered architect office or by a designated performance evaluation organization, and if this certificate has been issued for a property to be purchased, the following advantages can be obtained.

 

  1. 1. The property owner will be qualified for a tax reduction for housing loans.
  2. 2. Registration and license tax at the time of purchase will be reduced.
  3. 3. Real estate acquisition tax at the time of purchase will be reduced.
  4. 4. Fixed property tax will be reduced 50% at maximum for a year.
  5. 5. Earthquake insurance premium will be reduced 10%.

 

Although a building that meets the new earthquake resistance standard is more resistant to earthquakes in terms of expected degrees of damages and probability of being damaged compared to one that meets the old earthquake resistance standard, there is no such thing as a 100 percent earthquake resistant building, even if the building meets the new earthquake resistance standard. To find a truly safe house, it is necessary to collect information from perspectives other than those of earthquake resistance standards.

What is the seismic performance level of the building?

Seismic performance level

With the introduction of the Housing Performance Indication System in 2000, the seismic performance level, the level of resistance of the framework structure from collapsing during earthquakes, is now indicated and has become an effective criterion for judging the safety during an earthquake. There are levels 1 to 3; level 1 buildings have about the same seismic performance as the Building Standards Act compliant buildings; level 2 buildings will not collapse in an earthquake 1.25 times stronger than level 1 buildings can handle; and level 3 buildings can survive an earthquake 1.5 times stronger than level 1 buildings can handle. As the Building Standards Act sets out a minimum level of seismic performance, buildings with a seismic performance level of 2 or above will be safer during an earthquake. In addition, discounts can be applied to earthquake insurance premiums in some cases depending on the buildings’ seismic performance level.

Are the wall quantities, metals and foundations capable enough to resist earthquakes?

Wall quantities, metals, and foundations

In Japan, standards and criteria such as the above are used as an indicator of seismic performance of the building itself. Factors that influence such performance include wall quantities, metals, and foundations. If there are many bearing walls supporting the construction and they are arranged with good balance throughout the building, the construction will be resistant to earthquakes. If wood is used in the construction, using reinforcement metals can strengthen the joints. Foundations, the very bottom of a building, also largely influence its seismic performance. Continuous footing is a foundation consisting of continuous concrete strips, formed around the building to support it. Mat foundation is established by creating a steel reinforced concrete surface with a thickness of about 150mm under the entire floor in addition to continuous footing. With mat foundation, the foundation becomes more integrated, and as buildings are supported by a surface rather than lines, the seismic performance will be higher.

In the significant revision of the Building Standards Act made on June 1, 2000, provisions were included for the allocation balance of bearing walls in addition to the wall quantities, and specified which metal should be used in joints. From this, buildings constructed on or after June 1, 2000 (buildings for which building verifications were applied for on or after June 1, 2000 to be precise) can be said to have higher seismic performance than those constructed before such revision.

 

Which structure type does the building use?

Structural types

The structure of a building can be categorized into different types based on the materials used, such as wooden structure, RC (reinforced concrete) structure, S (steel) structure, and SRC (steel reinforced concrete) structure. RC structure is a structure made with reinforcing steel frames covered with cement, while S structure uses steel frames inside pillars and beams. SRC structure combines the strengths of both RC structure and S structure, placing reinforcing steel as the core of reinforced concrete, and is used in high-rise buildings as it secures high seismic performance.

In terms of the way to combine the structural material of buildings, there are two types of structures: the rigid frame structure and the box frame structure. While rigid frames support the weight of a building with pillars and beams, box frames support the weight with walls. As box frames need more bearing walls, windows tend to be smaller leading to less freedom in renovation works. However, the solid walls of box frame buildings will prevent its collapse during an earthquake.

Which construction method was used for the building?

Construction methods

Latest technologies are being developed from the viewpoints of seismic isolation, seismic control and damping, advancing from the perspective of being quake-proof, which focuses on the strength of the building itself based on the Building Standards Act. Especially since the 1995 Great Hanshin Earthquake, construction technologies to secure safety during an earthquake have developed dramatically. A quake-proof structure is a structure designed to withstand the forces that occur on buildings during an earthquake. However, during a massive earthquake, there are possibilities of furniture falling and breaking and glasses shattering from large quakes. On the other hand, with a seismic control structure, dampers that absorb vibrations are placed within a building and prevents the building from deformation by resisting and damping the vibration. There are wall-type, brace-type and cylinder-type dampers, and each of them absorbs energies from an earthquake. In a seismically isolated structure, a seismically isolating device made of laminated rubber bearings is set between the ground and the building to ward off vibration. With this, greater safety can be expected as earthquake-related energies reaching a building are weakened. Recent super high-rise buildings in Japan utilize hybrid structures that combine several seismic control and seismically isolated structures. Active-vibration controls, which utilize IT, are also becoming popular. Further, damping technologies, which use the movement of additional mass placed on the rooftops or the top floor as a damper, are being introduced as well.

 

What are the risk levels of the ground and area?

Ground

All of the above technologies are focused on the building itself, however, even if the building is strong and has countermeasures against vibrations, weak ground can lead to damages during a massive earthquake. In the Great East Japan Earthquake, liquefaction caused buildings and roads to subside and tilt, and lifelines such as water pipes were affected. Liquefaction does not just occur anywhere; it occurs when three factors of soft sand ground, shallow ground water level and massive long-lasting earthquake happen at the same time. Therefore, in order to avoid damages, it is important to know about the ground of the area where the building is located. If the ground was formed long ago and is mainly made up of a diluvium, an earthquake’s energy is less likely to be amplified, so damages are less likely to occur in such area. On the other hand, if the ground is formed rather recently and is mainly made up of an alluvium, energy can easily be amplified and the area will be prone to liquefaction. You can refer to hazard maps released by prefectures on their website for information on liquefaction and other natural disasters.

 

Area risks

In Tokyo, the collapsing risk, which indicates the buildings’ risks of collapsing and tilting due to earthquakes, are being measured based on the types of buildings and classifications of grounds, and the results of the measurement are released publicly. The general risk level of each area is measured based on such collapsing risk and conflagration risk, that is, the risk of fires spreading. The conflagration risk is measured based on factors such as the structure of buildings and gaps between buildings. When searching for real estate properties, in order to find a building that is safe in many aspects, it is important to bear in mind that fires can also cause significant damages during an earthquake.

 

 

 

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