How Japan mastered art of earthquake-proofing its buildings

Japan is known for having excellent building structures that can survive strong earthquakes above magnitude 7, because it is located in a region where many earthquakes happen.

The country has two standards of earthquake safety: If a building is harmed by a minor earthquake, it has to be reconstructed with the newest earthquake-proof features; if a building is harmed by a major earthquake, some material damage is allowed as long as no one is hurt or killed.

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

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 intense earthquakes, as well as volcanic eruptions and tsunamis. According to the EarthScope Consortium, Japan experiences around 1,500 noticeable earthquakes each year, some of which can cause widespread damage and casualties.

The most destructive earthquake in Japan’s 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 main goal of earthquake-resistant design is to prevent the collapse of buildings and protect the lives of the occupants. To achieve this, buildings have to withstand the horizontal and vertical forces of the earthquake, as well as the aftershocks and secondary effects such as fire and flooding. Buildings also have to absorb and dissipate the seismic energy as much as possible, to reduce the stress and deformation on the structure.

Age-old techniques

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

The Wood also has a low thermal conductivity, meaning that it does not conduct heat well, which reduces the risk of fire.

Wooden buildings in Japan are often constructed using a traditional method called post-and-beam. This method involves erecting vertical wooden posts that support horizontal beams, which in turn support the roof and the floors. The posts and beams are connected by joints that allow some movement and rotation, which makes the structure more adaptable to the ground motion. The joints are also reinforced by metal brackets, nails, or bolts, which prevent the structure from falling apart.

One of the most iconic examples of wooden buildings in Japan is the pagoda, a multi-story tower that is often found in Buddhist temples. Pagodas are designed to be stable and durable, despite their height and slender shape. One of the secrets behind their stability is the use of a central pillar, called the shinbashira, which runs through the core of the pagoda and acts as a shock absorber.

The shinbashira is loosely connected to the floors, which allows it to sway independently from the rest of the structure. This reduces the resonance and amplification of the seismic waves, and prevents the pagoda from toppling over.

Dampers

Another technique that Japan has used to make its buildings earthquake-proof is the use of dampers, which are devices that reduce the vibration and oscillation of a structure. Dampers work by converting the kinetic energy of the 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 external power or control. Passive dampers can be made of various materials, such as rubber, steel, or concrete, that have high damping properties. Passive dampers can be installed in various parts of the structure, such as the base, the walls, the columns, or the beams, to provide additional stiffness and damping.

Active dampers are more advanced and sophisticated type of dampers, which require external power and control. Active dampers can sense the motion of the structure and adjust their damping force accordingly, to counteract the seismic waves.

These dampers can be based on various mechanisms, such as hydraulic, pneumatic, electromagnetic, or piezoelectric, that can generate and apply a controlled force. Active dampers can be installed in various parts of the structure, such as the roof, the floors, or the braces, to provide additional control and stability.

Protective mesh

Another technique that Japan has used to make its buildings earthquake-proof is the use of protective mesh, which is a net-like material that covers the exterior of the structure. Protective mesh serves two purposes: to prevent the falling of debris and to reduce the impact of flying objects.

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

Mesh can prevent the falling of debris, such as glass, concrete, or metal, that can be caused by the cracking or breaking of the structure. Protective mesh can catch and hold the debris, preventing it from injuring people or damaging the property below. Protective mesh can also reduce the impact of flying objects, such as cars, trees, or poles, that can be propelled by an earthquake or tsunami. This Protective mesh can deflect and absorb the kinetic energy of the objects, reducing the force and damage to the structure.

Shock absorbers

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

Base isolation is a way of absorbing shocks that puts the structure on a base that can bend or slide, which makes the seismic waves weaker. The Base isolation can use different materials, like rubber, steel, or lead, that can stretch or resist movement. Base isolation can also use different devices, like rollers, bearings, or springs, that let the base move or turn.

The Seismic isolation is a way of absorbing shocks that puts the structure on a base that is hard or fixed, which makes the structure vibrate faster. Seismic isolation can use different materials, like concrete, steel, or carbon, that are stiff or strong. Seismic isolation can also use different devices, like braces, columns, or walls, that give more support and strength.

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