Earthquake-Resistant Building Technology
After a large earthquake, the news inundates us with images of crumbled concrete, twisted steel, and disaster recovery teams searching through rubble for survivors. According to the California Department of Conservation, the 1989 Loma Prieta earthquake caused 63 deaths, and 3,757 people reported injuries from the disaster. The World Health Organization says that earthquakes caused nearly 750,000 deaths worldwide between 1998 and 2017. And more than 125 million people were affected, either through injuries or displacement.
Earthquakes themselves didn’t cause these deaths and injuries. Collapsed buildings, roads, and bridges were the greatest danger. As an industry adage says, earthquakes don’t kill people; buildings do.
Though earthquakes are uncontrollable, earthquake damage to people and property is predictable and preventable with earthquake engineering and earthquake-resistant building technology. While an earthquake-proof building is impossible, at least for the foreseeable future, earthquake resistance is possible with a holistic, cohesive approach.
Elements of an Earthquake-Resistant Structure
In the many parts of the world with frequent seismic activity, building earthquake-resistant structures is now common practice. While geophysicists and seismologists have made great advancements in early warning systems, they cannot yet predict exactly where, when, and how strongly an earthquake will strike. As the earth’s crust constantly changes, new seismic zones may emerge and long-existing zones may shift and change. Thus, all communities can benefit from knowledge of earthquake-resistant building technology.
Why Structures Fail in an Earthquake
Earthquakes occur when tectonic plates in the earth’s lithosphere (the mantle and crust) grind together and then suddenly shift. The shift produces a massive energy release that travels from the epicenter through the ground in concentric waves.
These waves then move through structures in both vertical and horizontal waves, stressing foundations, walls, and connections between materials. Most structures are designed to handle vertical forces, such as gravity and their own weight. They fail in an earthquake primarily because of the horizontal forces, which normal building codes don’t account for.
You can also view structural failure in terms of harmonics. All physical objects vibrate at a certain rate when force is applied, much like a tuning fork. When the vibration of seismic waves matches that of a structure’s harmonic frequency, the vibration is amplified.
In earthquakes, some of the damage is immediate, catastrophic, and obvious. Other damage can be more insidious. For example, seismic vibration could separate roof flashing, the material that directs water away from vulnerable connection points in the roof. Then water can enter the structure (sometimes unnoticed) and cause damage later.
Fine cracks that can appear in columns or beams are another example. These cracks may not be apparent to the human eye, but they make their presence known when the next natural disaster strikes.
Methods for Earthquake Resistance
Methods for making a structure earthquake-resistant involve either deflecting, absorbing, transferring, or distributing vibrations from seismic activity. Those methods come into play with building design. A more holistic, proactive approach is seismic design. This process analyzes both the site and the surrounding area before building design begins.
In addition to analyzing the site’s geological features, other seismic hazards and other types of disaster are considered. For example, what communications technology or other utilities could be disrupted? How might nearby buildings impact or be impacted by the new building? Could nearby bodies of water cause flooding, either through a tsunami or a seiche?
All these considerations help establish priorities and inform which seismic resistance techniques to use. This holistic approach has the added benefit of hardening buildings against other threats, from terrorism to high-speed winds.
Earthquake Resistance Techniques to Protect Buildings and Inhabitants from Seismic Threats
Environmental monitoring and early-warning systems are continuously improving and may become the most effective way to protect buildings’ inhabitants from seismic threats. However, 5G deployment challenges continue to inhibit communications-related solutions in rural and low-income areas. Therefore, building earthquake-resistant structures remains paramount.
Making buildings resistant to earthquakes begins with the soil beneath it. Soft, silty soils are prone to liquefaction during earthquakes. Liquefaction is when soil temporarily behaves like a liquid. Soft soils can also amplify vibrations. Any structure on such soil is at risk. An earthquake-resistant building is best located on solid ground.
When existing structures aren’t located on solid ground, deep-mixing and compaction-grouting techniques can be applied to protect them from seismic threats. Compaction grouting involves adding cement-like materials to the soil around footings and pressurizing it. Deep mixing involves inserting diaphragms around the foundation and into an impervious layer and then pumping out any groundwater within the diaphragms.
Where to Employ Earthquake-Resistance Techniques within a Building
Earthquake-resistance techniques can be used throughout a building, from foundation to roof and exterior to interior. The specific technique depends on the type of vibration control ideal for that location.
A base isolator allows the foundation to move separately from the main building structure. This flexibility prevents most seismic vibrations from entering the structure.
Seismic dampers can be used throughout the foundation and structure to absorb vibrations from earthquake forces. Dampers come in a variety of forms. For example, viscous dampers use hydraulics to dissipate energy. A tuned mass damper uses weight at the top of or at critical points throughout a structure to counteract ground motion. Friction dampers are like the brakes in most cars, converting movement to heat.
Structural reinforcements transfer or distribute vibrations to decrease their impact. For example, shear walls transfer vibrations to the foundation. Floors and roofs built as diaphragms distribute vibrations across the horizontal structure and into stronger vertical structures. Moment-resistant frames help connection points remain secure while allowing columns and beams to move without damage.
Nonstructural elements of the building can also cause significant injuries during an earthquake. In fact, a study in New Zealand showed that while failed structural elements caused the most fatalities, damaged nonstructural elements caused exponentially more injuries. The elements that caused the most injuries were furniture, shelving, suspended ceilings, and HVAC equipment and ducting.
The Federal Emergency Management Agency published an extensive guide on reducing risks of nonstructural earthquake damage. And cities in active seismic zones often have seismic building codes that address bracing guidelines for nonstructural elements.
New Building Materials for Earthquake-Resistant Construction
The best earthquake-resistant construction materials have an important quality in common: high ductility. Ductility refers to the material’s ability to move and change shape without breaking or losing strength. Traditionally, steel and wood are the best and most common earthquake-resistant materials.
Masonry and concrete have the lowest ductility. Unfortunately, many buildings erected prior to the 1950s used exactly those materials. Reinforcing or wrapping masonry and concrete can make such foundations and structures strong in an earthquake, which new materials are making increasingly possible.
New Materials
Scientists and engineers are developing new building materials for earthquake-resistant construction. These materials range from shape-memory alloys to invisibility cloaks to fibers created from synthetic spider silk.
Shape-memory alloys (SMAs) are fabricated metals that only change shape when cold and then return to their original shape when heated. “Cold” in this case could be as low as -100 degrees Celsius (-148 Fahrenheit). SMAs are highly ductile and create a damping effect due to their ability to dissipate heat.
Seismic invisibility cloaks are concentric rings of material surrounding a building’s foundation. These rings divert seismic waves around buildings. Scientists are still experimenting to find ideal materials (plastic, metal, trees, etc.) and configurations to create these rings. The drawback to this method is that it simply displaces vibrations instead of dissipating them. The risks to surrounding properties remain.
Spider silk is highly elastic yet stronger than steel. Its synthetic cousin displays similar properties, and manufacturers are racing to perfect it. The exact application in construction is yet to be determined. Theoretical construction-related applications include power grids, data networks, building cladding, scaffolding, and frames.
Technology-Based Techniques to Build Earthquake-Resistant Structures
New technology plays an important role in expanding our understanding of earthquakes and developing creative solutions to build earthquake-resistant structures. Seismic retrofitting, seismic analysis, and seismic sensors are aspects of this process.
The Importance of Seismic Retrofitting
According to researchers at Georgia Tech University, “nonductile concrete buildings are among the most common structures in the United States” and the most deadly. Older buildings may not have had the benefit of the seismic building codes at the time of their construction and thus require seismic retrofitting. Seismic retrofitting is extremely important to protect people and property in seismic zones.
This issue is about more than foundations, walls, and roofs. Consider utility lines (power, data, water, and gas) and how they might be impacted by an earthquake. If a building shifts, gas lines may separate and break, typically at connection points, but gas will continue to flow and fill the space. People in the space are then in danger of inhaling the gas, or the gas could ignite. Retrofitting gas lines may require multiple methods for maximum safety, including gas shut-off valves and flexible connections.
Many of the techniques already mentioned can be applied to existing structures to protect them from seismic threats. The most common retrofits include strengthening connections between building elements, adding steel frames, and isolating the base. Renovations can include other new technology—such as energy and water efficiency, air quality control, a , and fiber-optic cabling.
It’s also worth noting that not all buildings are good candidates for retrofitting. With the help of a seismic design, you may discover that it’s more cost effective to remove the old building and build a new one.
Seismic Analysis
Structural engineers use seismic analysis in earthquake engineering to predict how a structure will perform during seismic activity. While seismic building codes may specify which type of analysis is required in particular zones, engineers use a variety of models for full assessments.
Available models include equivalent static analysis, response spectrum analysis, linear dynamic analysis, nonlinear static analysis, and nonlinear dynamic analysis. Each type of analysis uses computer modeling for the complex calculations. With adequate seismic sensor data, artificial intelligence and machine learning can identify risks, structural faults, and even subtle fault lines that humans cannot.
Seismic Sensors and Warning Systems
Monitoring seismic activity is important both to give structural engineers data about a site’s geological features and to improve early-warning systems. As mentioned previously, predicting earthquakes isn’t an exact science, but sending out alerts when an earthquake is happening is more feasible. Seconds make a difference in getting people to safety, particularly for those farther from the epicenter.
Ocean-based sensors can also detect underwater earthquakes to predict tsunamis and send alerts that include wave height and arrival time. When Tonga erupted in January 2022, sending a tsunami across the globe, the US National Oceanic Atmospheric Administration issued a tsunami advisory. Coastal areas received the information and were prepared well in advance of the wave’s arrival.
The phrase “seismic sensors” conjures an old pen-and-pendulum seismograph transcribing ground motion onto paper. However, seismic sensors have come a long way and diversified to sense different frequencies for different applications. Increasingly, these sensors are creating an Internet of Things network reliant on edge computing.
Edge computing, as opposed to cloud computing, brings data processing and storage physically closer to users to increase speed and decrease bandwidth use. The edge ecosystem requires robust, reliable internet service, as does sending out alerts and coordinating disaster recovery after an earthquake.
Holistic Earthquake Resistance
Earthquake resistance requires a holistic, cohesive approach that uses the latest trends in technology on multiple fronts. Earthquake-resistant building technology, seismic monitoring, early-warning systems, and natural disaster response all exist in the same system and should be treated accordingly. This approach will save lives and protect property.
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