Earthquake Resistant Building Procedure
Before building, engineers evaluate the seismic activity of the area where they are building at. In the USA, they have the 'National Seismic Hazards Maps' from the US Geological Survey (USGS). These maps show the ground motion. Geologists then try to make an educated guess about ground motions from future earthquakes using earthquake data from the past.
This shows which areas of the US have the highest earthquake hazard.
“If our buildings are strong,” Michael Blanpied, associate coordinator of the USGS Earthquake Hazards Program, says, “then it does not matter so much [if we can predict large earthquakes] because we’ll be safe no matter when the ground happens to shake.”
Building Codes
In the US, they have an 'International Building Code'. They tell information about how to design structure so as they would not collapse based on the map above. Once engineers determine the seismic risks of a site, they start building. However, they must avoid irregular or asymmetrical designs like L-shaped or T-shaped structures. Ornaments are also limited like cornices or fascia stones because earthquakes can easily break these. In general, engineers and architects try to build and design symmetrical buildings so that they are able to withstand seismic waves.
If a building's foundation sits on soil, the whole building may collapse in an earthquake because of liquefaction regardless of the advanced building techniques For example, earthquakes often knock buildings off from their foundations. Over the recent decades, engineers have developed building codes so that buildings may not collapse when an earthquake occurs. These include:
If a building's foundation sits on soil, the whole building may collapse in an earthquake because of liquefaction regardless of the advanced building techniques For example, earthquakes often knock buildings off from their foundations. Over the recent decades, engineers have developed building codes so that buildings may not collapse when an earthquake occurs. These include:
- Base isolation - This means that a structure or a bridge is lifted off its foundation on supports made of rubber, springs bearings or padded cylinders. During an earthquake, the waves travel through them instead of the buildings because it cannot reach the building. Bearings attach to the building and foundation using steel plates and when an earthquake hits, the foundation only moves without moving the structure above it.
- Actively mass dampling - Roofs of buildings have counterweights that are connected to dampers. During an earthquake, these counterweights are moved automatically by the dampers to counter the shaking of the building. These dampers act as a shock absorber. When the building begins to wobble, the counterweights moves in the opposite direction, which reduces the vibrations.
- Ductility - Brick and concrete buildings are examples of low ductility. They absorb very little kinetic energy. This makes them especially vulnerable even in minor earthquakes. On the other hand, buildings constructed with steel concrete, can withstand much better because the steel increases the ductility of the material.
- Structural steel -- Steel components that come in a variety of preformed shapes, such as beams, angles and plates have the highest ductility, allowing buildings to bend without breaking.
Taipei 101
Taiper 101 is one of the world's tallest skyscrapers. It is 508 metres tall. It consists of an active mass damper at the top of the building. It is formed by eight steel cables and connect to eight dampers. If the building sways, the damper counteracts the motion, reducing vibrations that could cause stress on the structure.
Earthquake Resistant Building Designs
In earthquake prone countries, buildings are made earthquake resistant. Deep foundation and massive shock absorbers are laid down to lessen the kinetic energy of seismic waves. Skyscrapers are made so that they sway during a quake and not collapse. A building consists of columns, beams and bracing so as to transfer seismic forces to the ground. Engineers often build walls using braced frames, which depend on trusses to resist sideways motion.
Building Designs include:
Building Designs include:
- Diaphragms - They are a major component in buildings. They include floors of a building and its roof. Engineers place each diaphragm on its own deck and strengthen it so that when a vertical wave hits, the waves will have a lesser impact than before.
- Trusses - Diaphragms are not able to be built on roofs because strong decks are not possible on roofs. Instead, engineers strengthen the diaphragm with trusses. They are diagonal structures inserted into rectangular areas of the frame.
- Shear walls - These are walls that strengthens the frame of a building to help resist seismic forces and stop them from rocking. Engineers often place them on walls, but not around elevators or staircases.
The Transamerica Pyramid
In San Francisco towers a skyscraper called the 'Transamerica Pyramid' with an outstanding height of 260 metres. It is the tallest building in San Francisco and the eighth tallest in the world. The building's foundation is 2.7 m thick. The building uses trusses that have bracings that are x-shaped. It is resistant to the seismic waves. There are also interior frames other than exterior frames. The result is strong, fairing well during an earthquake. For example, during the Loma Prieta earthquake, which had a magnitude of 7.1, the top story of the pyramid swayed more than 30 centimeters from side to side, yet suffered no damage.
Smart Structures
Greg Deierlein of Stanford University and Jerome Hajjar of Northeastern University have designed a structure with fuses that collapses on purpose and then reform after the quake subsides.
“The building, in a sense, sacrifices itself to save the occupants,” says Gregory Deierlein, a Stanford University civil and environmental engineer.
They tested the structure on Japan's E-Defense shake table (the world's largest earthquake simulator). The fuses, made out of steel, successfully absorbed the shock of the earthquake which was more than magnitude 7.0. Afterwards, the deformed fuses could be replaced in around four days.
“The building, in a sense, sacrifices itself to save the occupants,” says Gregory Deierlein, a Stanford University civil and environmental engineer.
They tested the structure on Japan's E-Defense shake table (the world's largest earthquake simulator). The fuses, made out of steel, successfully absorbed the shock of the earthquake which was more than magnitude 7.0. Afterwards, the deformed fuses could be replaced in around four days.
Another idea is to include fiber-optic sensors that can sense when a structure is about to fall. Signals from the censors would then be sent to tiny ceramic strips built into the walls and the frame, which would afterwards change shape to absorb the wave energy. the sensors would then send signals to tiny ceramic strips built into the walls and frame, which would change shape to absorb the energy.
In Cary, North Carolina in the United States, Lord's Corporation's labs and the University of Notre Dame researchers have developed a product that can reduce the damage caused by earthquakes. It is called magnetorheological fluid (MR fluid), which is used inside dampers to make buildings stable. MR fluid is a liquid that changes to a near-solid when exposed to a magnetic force, then back to liquid once the magnetic force is removed.
During an earthquake, MR fluid inside the dampers will change from solid to liquid and back as a magnetic force inside the damper activates.
Dampers filled with the aforementioned fluid mitigate vibrations of buildings during an earthquake.
Another innovation is the seismic invisibility cloak. To do this, engineers would bury up to 100 plastic rings beneath the foundation of a building. When waves meet the rings, they enter and then become compressed. The waves just pass by, just beneath the building's foundation, exit the rings and resume their original speed.
The Japanese company Air Danshin developed a levitating house. It works by putting a deflated air bag under a house and when sensors feel an earthquake, they pump air into an airbag, inflating it and lifting the entire house around three centimetres off its foundation.
In Cary, North Carolina in the United States, Lord's Corporation's labs and the University of Notre Dame researchers have developed a product that can reduce the damage caused by earthquakes. It is called magnetorheological fluid (MR fluid), which is used inside dampers to make buildings stable. MR fluid is a liquid that changes to a near-solid when exposed to a magnetic force, then back to liquid once the magnetic force is removed.
During an earthquake, MR fluid inside the dampers will change from solid to liquid and back as a magnetic force inside the damper activates.
Dampers filled with the aforementioned fluid mitigate vibrations of buildings during an earthquake.
Another innovation is the seismic invisibility cloak. To do this, engineers would bury up to 100 plastic rings beneath the foundation of a building. When waves meet the rings, they enter and then become compressed. The waves just pass by, just beneath the building's foundation, exit the rings and resume their original speed.
The Japanese company Air Danshin developed a levitating house. It works by putting a deflated air bag under a house and when sensors feel an earthquake, they pump air into an airbag, inflating it and lifting the entire house around three centimetres off its foundation.
Minimising Earthquake Risks
People who study earthquakes are called seismologists. They look for ways to predict when and where earthquakes will strike. However, since earthquakes gives few warning signals, in countries located in the Pacific Ring of Fire, earthquake survival relies on being prepared.
How to minimise earthquake risks:
How to minimise earthquake risks:
- Build a house made of wood, not brick because they are not flexible.
- Lay foundations made of concrete.
- Build triangle structures because triangles are the strongest shapes.
- Add a mass damper on top of the building and a tendon system on the bottom because it will shift the weight around to make the building steady.
- Install base isolators so that it may absorb the seismic waves.
- Put flexible pipes so that water lines and gas lines would not leak.