All You Need to Know About Earthquake-Resistant Foundation

 A detailed guide about earthquake-proof foundations and their specifics

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If you live in an area that is predisposed to earthquakes, and you want to buy or build a house there, your very first concern would be to build a foundation for your property that will be able to withstand earthquakes without being damaged. 

In this article, we will tell you more about earthquake-resistant foundations. In particular, you will learn what kind of foundation it is and what makes it different from regular house foundations. Also, you will learn what benefits such foundations have and what you can do to improve the way the building foundation system responds to seismic waves.

A sturdy house foundation built to withstand earthquakes
Earthquake-Resistant Foundation. itishouse.com

What Is an Anti-Earthquake House Base?

Simply speaking, an earthquake-proof foundation is the type of a house foundation that can withstand seismic waves. Such foundations are used for houses that sit on soft or filled-in soil mostly. In this case, the building is more prone to damage than a house built on firm and solid ground and may fail in an earthquake regardless of the engineering techniques used.

This is why engineers have created different ways of improving the building-foundation system to enable it to respond to seismic waves. Some of the most commonly used ones include:

  • Tying the foundation to the building, which makes the whole structure move as a unit.
  • Base isolation involves floating a building above its foundation. This method uses a system of bearings, springs, or padded cylinders.
  • Active mass damping. It uses a heavy mass mounted to the top of a building and connected to viscous dampers that work like shock absorbers.
Drawing of a house with a protected foundation
By vista.com

If you are planning to build a house in an area with soft soil and high seismic activity, you should know what anti-earthquake options are available and how they work. But first, it is essential to realize how earthquakes affect our houses in general.

How Does Earthquake Impact Buildings?

When an earthquake occurs, shockwaves are sent and spread throughout the ground in short rapid intervals that extend in all directions. However, most buildings are not ready for this kind of stress! The majority of buildings (both residential and non-residential) are generally created and constructed to handle vertical forces from their weight and gravity. But they cannot traditionally handle side-to-side forces that are emitted by earthquakes.

Earth oscillation amplitude fixed on paper
By vista.com

When such horizontal movements occur, they lead to the vibration of walls, floors, columns, beams, and the connectors that hold all of them together. And even if the earthquake is not strong or doesn’t last long, the difference in movement between the bottom and top of the building produces extreme stress. As a result, the supporting frame ruptures, and the entire structure collapses eventually.

Among the typical kinds of damage caused by earthquakes, there are:

  • Cracked walls
  • Buildings being knocked from their foundations
  • Walls deformation
  • Dissipation of a building
  • Building damping
  • Building oscillation

This is why, as a homeowner, you should be aware of how to make your building resistant to seismic activity in your region. This way, you will bring down the possibility of the potential damage an earthquake may cause and make your home less prone to destruction. 

How to Make a Building Earthquake-Proof

A small gray house with a veranda
By vista.com

To design an earthquake-proof building, you will need the help of professional engineers that have experience in this field. They will estimate all the risks and work to reinforce the whole structure and counteract a potential earthquake’s forces. Here are some methods that are typically used to help buildings withstand earthquakes.

Start With Creating a Flexible Foundation

Buildings get ruined after earthquakes due to rigid foundations that can’t respond to earth vibrations appropriately. This is why one way to resist ground forces is to lift the foundation of a building above the ground. This is typically made by using a method called base isolation. 

Elevated building foundation
itishouse.com

This method is specifically popular when a house is at the beginning of the construction stage. In this case, a building is constructed on top of flexible pads made of steel, rubber, and lead. When the base moves during an earthquake, the isolators vibrate while the structure remains steady. This method helps to absorb seismic waves more effectively. As a result, they can’t be spread through the building.

Use Counter Forces to Prevent Damping

This method is somewhat similar to the one that shock absorbers use in cars. Engineers also use a version of shock absorbers to make buildings more earthquake-resistant. 

Like shock absorbers used in cars, the construction ones also reduce the magnitude of shock waves and help reduce the pressure an earthquake makes on the building. This is accomplished in two ways: vibrational control devices and pendulum power.

  • Vibration control devices include dampers placed at each level of a building between columns and beams. During an earthquake, the vibrational energy is transferred into the dampers, dissipating the force of the vibrations.
  • Pendulum power is primarily used in skyscrapers. It uses a large ball from steel cables connected to a hydraulic system at the top of the building. When the building begins to sway, the ball moves in the opposite direction, thus stabilizing the building.

Make a Shield to Protect a Building from Earthquake Vibrations

This method uses a so-called “seismic cloak.” This “cloak” involves creating a protective barrier of 100 concentric rings made of plastic and concrete. These rings are buried at least three feet beneath the foundation of the building.

When an earthquake occurs and seismic waves enter the rings, ease of travel makes these waves move through to the outer rings. As a result, they are essentially transferred away from the building and dissipated into the ground.

Make Sure to Reinforce the Building’s Structure

All You Need to Know About Earthquake-Resistant Foundation
By vista.com

To withstand collapse during earthquakes, buildings must be able to redistribute forces that travel through them during seismic activity. In most cases, engineers use shear walls, cross braces, diaphragms, and movement-resisting frames for reinforcing a building.

Shear walls, for example, can help transfer earthquake forces and seismic waves. They are made of multiple panels, helping a building keep its shape during swaying. Shear walls are often supported by diagonal cross braces made of steel. These beams can support compression and tension, helping to counteract pressure and push forces.

Diaphragms are another part of a house reinforcement system. They consist of the building’s floors, roof, and decks placed over them and help remove tension from the floor. As a result, seismic forces are pushed to the building’s vertical structures.

Finally, there are movement-resisting frames. These ones provide additional flexibility to a building. The movement-resisting frames are placed among a building’s joints, allowing columns and beams to bend while the joints remain rigid. Thus, the building can resist the larger forces of an earthquake.

Now you know not only how earthquakes may affect a house, but you also know what methods are used for reinforcing a building to make it more seismic-proof. This will help you understand how anti-earthquake methods work, which is crucially important if you are building a house for yourself in an area with high seismic activity.

What Materials Are Used For Making a Building Earthquake-Resistant

As you already know, there are different methods used by engineers for reinforcing a building and making it seismic-proof. The most common methods include shock absorbers, pendulums, and anti-earthquake “cloaks.”

On the one hand, using these tools may help you keep your home safe and not collapse during an earthquake. However, the materials you choose for constructing a building are equally responsible for its seismic stability!

Steel and Wood

To be able to resist stress and vibration that occur during an earthquake, the material must have high ductility, which means the ability to undergo large deformations and tension that occur during even the weakest seismic activity. 

In this regard, structural steel is a very beneficial material. This material comes in a variety of shapes and allows buildings to bend without breaking. This is why modern buildings are often constructed with structural steel. Wood is another material that can be helpful thanks to its surprising properties, such as high strength relative to its lightweight structure.

Innovative Materials

Although wood and structural steel are popular materials for constructing seismic-proof buildings, scientists and engineers have developed new building materials that possess even more excellent shape retention. For example, there are innovative shape memory alloys. They have the ability to both endure the heavy strain and revert to their original shape. In addition, they also include fiber-reinforced plastic wrap made from a variety of polymers. This extra component can be wrapped around columns, providing up to 38% added strength and ductility!

Of course, engineers don’t forget about the natural elements to use for reinforcing buildings. For example, they consider the sticky yet rigid fibers of mussels and use qualities of a spider web (like its strength) in creating seismic-proof structures. 

Also, bamboo and 3D printed materials are taken into consideration thanks to their lightweight, interlocking structures and limitless forms. These materials inspired by nature can potentially provide even more excellent resistance for buildings.

Now you know more about earthquake-proof foundations. You learned what type of foundation it is, how it works, and what benefits it has for a building. For example, compared to a regular rigid foundation, its more flexible seismic-resistant alternative will help a building to remain stable and avoid being damaged during earthquakes. Buildings with seismic-proof foundations often avoid such negative earthquake impacts as broken walls, deformations, dissipation, and others.

We also told you how earthquakes might affect your home and what types of reinforcing methods engineers use to keep buildings safe and sound. Finally, you learned what materials are used for this purpose.

Facts

The development and implementation of earthquake-resistant foundations is a testament to human ingenuity in the face of nature's most unpredictable and devastating phenomena. With every earthquake, we gain valuable knowledge to improve our designs and safeguard our structures, making this a dynamic and continually evolving field of study.

  1. The Oldest Seismically Isolated Building: The first building to use base isolation for seismic resistance was the Foothill Communities Law and Justice Center in Rancho Cucamonga, California, in 1985. This marked a significant step forward in seismic engineering.
  2. Bearing Wall Foundation: In seismic-prone regions, many residential homes are built with a bearing wall foundation system. This type of construction helps distribute the seismic load throughout the structure, enhancing its resistance to earthquakes.
  3. Flexible Foundations: When it comes to earthquake-resistant design, flexibility is crucial. A structure that can bend without breaking is more likely to withstand the intense pressure of an earthquake. This has led to the use of flexible materials in foundations, such as rubber, combined with reinforced concrete or steel.
  4. Raft or Mat Foundations: These types of foundations spread the weight of the building over the entire footprint, reducing the pressure on any single point. Raft foundations are particularly beneficial for structures built on soft or sandy soils where earthquake vibrations can be especially destructive.
  5. Reinforced Concrete Foundations: Reinforcing concrete foundations with steel bars (rebar) greatly enhances a building's resistance to the lateral forces produced during an earthquake. This is a common practice in earthquake-prone regions and a crucial element in the construction of skyscrapers and other tall structures.
  6. Dynamic Analysis: Engineers use computer simulations to predict how a structure will react to seismic activity. This dynamic analysis allows them to design foundations that will best withstand potential earthquakes in their specific locations.
  7. Importance of Soil Studies: The type of soil a building is constructed upon can greatly influence its earthquake resistance. Buildings on loose or sandy soils suffer more damage during an earthquake than those built on solid rock. Because of this, extensive soil studies are a critical component in the design of earthquake-resistant foundations.

History

Our story begins in ancient times, when the destructive power of earthquakes was attributed to the fury of gods. The earliest record of an attempt to design earthquake-resistant structures comes from the Indian subcontinent. The architectural treatise, Manasara, written in 5th to 6th-century AD, described some principles to make houses resilient to the shocks of an earthquake.

The concept of earthquake-resistant construction, however, really began to develop after the catastrophic earthquake in Lisbon, Portugal in 1755. This event led to the first scientific studies into earthquakes and how buildings respond to them.

Fast forward to the 20th century. After the tragic 1906 San Francisco earthquake, American engineers initiated the use of reinforced concrete to improve structural integrity during seismic events. The first building to use such design was the Ingalls Building in Cincinnati, Ohio, built in 1903.

In the 1970s, a significant innovation emerged, known as base isolation. The first building to use base isolation for seismic resistance was the Foothill Communities Law and Justice Center in Rancho Cucamonga, California, in 1985. The base isolation technology places shock absorbers at the foundation of the building, which helps to mitigate the seismic energy during an earthquake, keeping the building relatively steady.

Throughout the 1990s and into the 21st century, our understanding of earthquakes and how buildings can be designed to withstand them has grown exponentially. Engineers now use advanced computational modeling to predict how a building will respond to seismic forces. These dynamic analyses help engineers design and optimize earthquake-resistant structures.

A noteworthy development in the 21st century is the introduction of the "controlled rocking design" approach. This concept allows the building to rock during an earthquake and then re-centers it when the shaking stops. The first building to use this design was the 525 Golden Gate in San Francisco, completed in 2012.

Expert Advice

These tips are just the tip of the iceberg when it comes to constructing an earthquake-resistant foundation. The most important tip of all? Work with experienced professionals who can guide you through this complex process.

  1. Understand the Soil Type: The first step in creating an earthquake-resistant foundation is to understand the soil type on your site. Sandy or gravelly soils are usually good, while clayey or loose, water-saturated soils could lead to complications.
  2. Use Reinforced Concrete: Reinforced concrete foundations, when designed correctly, can resist earthquake forces more efficiently due to their increased ductility.
  3. Opt for Base Isolation Technique: This technique allows the base to move with the ground motion during an earthquake while the superstructure above remains relatively still. Rubber bearings, lead-rubber bearings or sliding plates are often used for this method.
  4. Consider Shear Walls: Shear walls, particularly in high-rise buildings, can help the structure resist lateral forces caused by earthquakes. These walls should be strategically placed to optimize the resistance.
  5. Reinforced Masonry: Brick or block masonry, when reinforced with steel, can provide a solid and earthquake-resistant foundation.
  6. Get a Geotechnical Report: It's important to hire a geotechnical engineer to assess the soil and geology of your site. The report will guide your architect or engineer in designing an earthquake-resistant foundation.
  7. Regular Maintenance: Like all parts of your home, the foundation needs regular inspection and maintenance. Even minor cracks could indicate problems that need attention.
  8. Work with a Structural Engineer: Hiring a professional who specializes in earthquake engineering will help ensure your foundation is designed to withstand seismic activity.
  9. Local Building Codes: Always comply with your local building codes. These regulations are designed to ensure your home can withstand the region's typical seismic activity.

 

Adequate Drainage: Ensure your property has adequate drainage systems. Waterlogged soil can compromise the strength of your foundation during an earthquake.

Frequently Asked Questions

Does An Earthquake-Resistant Foundation Cost More Than A Regular One?

Typically yes, a reinforced foundation costs more because it requires other materials and techniques to make it.

Can Any Construction Team Build A Seismic-Proof Foundation?

No. You should entrust your house foundation to constructors who have experience in building this type of foundation only!

How High Can A Building Be To Have A Seismic-Proof Foundation?

A building can be of any height, from a cabin to a skyscraper.
How Do Earthquake-Resistant Foundations Work?

These foundations work by incorporating structural elements that absorb and dissipate seismic energy, reducing the impact on the building.

How To Upgrade A Foundation After An Earthquake
  1. Post-earthquake, the foundation can be upgraded by conducting a thorough structural assessment to identify any damages. Upon completion of the assessment, repair or retrofit strategies such as epoxy injection or the installation of steel brackets can be implemented to address identified issues.
  2. The use of base isolation systems can be a robust upgrade strategy for a foundation after an earthquake. Although expensive and labor-intensive, it provides excellent seismic performance by allowing the structure to move with the ground, reducing the forces transmitted to the building.
  3. Foundation upgrade after an earthquake could involve soil improvement techniques such as compaction or grouting. Improving the soil's strength and stiffness can significantly enhance the foundation's seismic resistance for future events.
  4. Incorporating energy dissipation devices can be an effective way to upgrade a foundation post-earthquake. These devices, designed to absorb and dissipate seismic energy, can reduce the forces experienced by the structure in subsequent seismic events.
  5. Post-earthquake foundation upgrade may necessitate the installation of additional reinforcing steel or the construction of shear walls. These measures can significantly increase the structural integrity and seismic resistance of the foundation.
  6. An effective strategy for upgrading the foundation after an earthquake is retrofitting with reinforced concrete. This technique, which involves adding new concrete and reinforcing steel, can significantly enhance the foundation's ability to withstand future seismic events.
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