How Japan mastered the art of earthquake-resistant buildings

Japan is known for having excellent building structures that can withstand strong earthquakes greater than 7 magnitude, because it is located in an area where many earthquakes occur.

The country has two earthquake safety standards: If a building is damaged by a minor earthquake, it must be rebuilt with the latest earthquake-resistant features; If a building is damaged by a major earthquake, some physical damage is allowed as long as no one is injured or killed.

Japan is one of the most earthquake-prone countries in the world, with thousands of earthquakes occurring every year. To protect its people and infrastructure from the devastating effects of seismic waves, Japan has developed a variety of technologies and techniques to make its buildings more resilient and earthquake-resistant.

The need for earthquake-resistant design

Japan is located along the Pacific Ring of Fire, where four tectonic plates meet and collide. This causes frequent and severe earthquakes, as well as volcanic eruptions and tsunamis. According to the EarthScope Consortium, Japan experiences about 1,500 notable earthquakes each year, some of which can cause widespread damage and casualties.

The most devastating earthquake in Japanese history was the Great Kanto Earthquake of 1923, which killed more than 140,000 people and destroyed hundreds of thousands of buildings in Tokyo and Yokohama. Since then, Japan has learned from its past disasters and implemented strict building codes and regulations to ensure the safety and durability of its structures.

The hill on which Himeji Castle was built was first fortified in 1333 AD. Image source: Himeji Castle/Andre Doiron (CC BY-ND)

The main goal of earthquake-resistant design is to prevent building collapse and protect the lives of its occupants. To achieve this, buildings must withstand the horizontal and vertical forces of the earthquake, as well as aftershocks and secondary impacts such as fires and floods. Buildings must also absorb and dissipate seismic energy as much as possible, to minimize stress and deformation on the structure.

Old technologies

One of the oldest and most effective techniques that Japan has used to make its buildings earthquake-resistant is the use of wood. Wood is a flexible, lightweight material that can bend and swing without breaking. Wood also has a high strength-to-weight ratio, meaning it can handle heavy loads with minimal mass.

Wood also has low thermal conductivity, meaning it does not conduct heat well, reducing the risk of fire.

Wooden buildings in Japan are often constructed using a traditional method called columns and beams. This method involves erecting vertical wooden columns that support horizontal beams, which in turn support the roof and floors. The columns and beams are connected by joints that allow some movement and rotation, making the structure more adaptable to ground movement. The joints are also reinforced with metal brackets, nails or screws, which prevent the structure from collapsing.

Six overturned buildings (A-F) in the town of Onagawa and the mechanisms that mediated the overturn. Image credit: Wikimedia Commons

One of the most famous examples of wooden buildings in Japan is the pagoda, a multi-story tower often found in Buddhist temples. The temples are designed to be stable and sturdy, despite their height and slim shape. One of the secrets to its stability is the use of a central column called a shinbashira, which runs through the core of the pagoda and acts as a shock absorber.

The shinbashira is loosely attached to the floors, allowing it to swing independently from the rest of the structure. This reduces the echo and amplification of seismic waves, and prevents the pagoda from toppling over.

Dampers

Another technique Japan has used to make its buildings earthquake-resistant is the use of dampers, which are devices that reduce the vibration and oscillation of the structure. Dampers work by converting the kinetic energy of motion into heat, which is then dissipated into the environment. Dampers can be classified into two types: passive and active.

These passive dampers are the simplest and most common type of dampers, which do not require any power or external control. Passive dampers can be made of different materials, such as rubber, steel or concrete, which have high damping properties. Passive dampers can be installed in various parts of a structure, such as the base, walls, columns or beams, to provide additional stiffness and damping.

Wooden buildings in Japan are often constructed using a traditional method called columns and beams. Image source: UC San Diego Jacobs College of Engineering/CC 3.0

Active dampers are a more advanced and sophisticated type of damper, which requires external energy and control. Active dampers can sense structure movement and adjust the damping force accordingly, to counter seismic waves.

These dampers can rely on different mechanisms, such as hydraulic, pneumatic, electromagnetic or piezoelectric, which can generate and apply a controllable force. Active dampers can be installed in various parts of the structure, such as the roof, floors or supports, to provide additional control and stability.

Protective net

Another technique that Japan has used to make its buildings earthquake-resistant is the use of protective mesh, a mesh-like material that covers the outside of a structure. The protective net serves two purposes: preventing falling debris and reducing the impact of flying objects.

This mesh is made of different materials, such as steel, nylon, or fiberglass, with high tensile strength and durability. The protective net can be attached to the structure by hooks, clips or cables to form a flexible and flexible barrier. The protective mesh can also be designed in different shapes and patterns to enhance the aesthetic and architectural value of the structure.

The mesh can prevent falling debris, such as glass, concrete or metal, that can be caused by a cracked or broken structure. The protective net can capture and retain debris, preventing it from injuring people or damaging property below. The protective net can also reduce the impact of flying objects, such as cars, trees or poles, that can be pushed by an earthquake or tsunami. This protective mesh can deflect and absorb the kinetic energy of objects, reducing force and damage to the structure.

Shock absorption

Another method that Japan has used to make its buildings earthquake-resistant is the use of shock absorbers, which are devices that isolate the structure from ground movement. Shock absorbers work by creating a gap or buffer zone between the base of the structure and the foundation, allowing the structure to move independently of the ground. Shock absorbers can be classified into two types: basic isolation and seismic isolation.

Base isolation is a shock-absorbing method that places a structure on a base that can bend or slide, making seismic waves weaker. To insulate the base can use different materials, such as rubber, steel or lead, that can expand or resist movement. Base insulation can also use various devices, such as pulleys, bearings, or springs, that allow the base to move or rotate.

Seismic isolation is a shock-absorbing method that places a structure on a solid or stable base which makes the structure vibrate faster. Seismic isolation can use different materials, such as concrete, steel or carbon, that are rigid or strong. Seismic isolation can also use different devices, such as arches, columns or walls, that provide additional support and strength.

Read on

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