By Anoushka Knowles
In 2017, over 200 people were killed during an earthquake in Mexico. The majority of deaths in earthquakes are caused because of damage to buildings. The damage can lead to collapse or dangerous falling parts which is what often leads to loss of life. Though earthquakes have been affecting civilizations for centuries, the industrial revolution and subsequent increase in the height of buildings only posed more danger during earthquakes. The taller buildings could be very dangerous as they put more weight on the foundation and could cause collapse. The base would be shaken, and the stuff rods that hold up the building would prevent any flexibility and movement, leading to a collapse. Thus, the need for earthquake resistant building design was created.
What is earthquake resistance?
When you think about the events of an earthquake, the quake itself is rarely the cause of death or injury. Rather, factors such as seismic waves cause damage, inducing deadly tsunamis, landslides, or building collapse. Because of this, it’s important that our buildings are designed with the intent to do the least harm during an earthquake. This is called earthquake resistance, which focuses on protecting human life. Damage to the building is a second priority. Buildings are constructed to survive seismic waves and remain standing. While there could be significant damage to the interior of the building, it’s important that the frame remains standing. If the frame were to collapse, everyone inside or even in proximity to the building would be at risk.
While earthquakes are still deadly, the idea of earthquake resistance is not new. One prime example of this are the ancient Japanese pagodas which have remained standing through 46 high-magnitude earthquakes. This was incredibly surprising, as they were able to withstand earthquakes that collapsed the newer, concrete buildings. Further research revealed that the Japanese architects knew what took others much longer to discover. They utilized the “snakedance theory”, in which they designed their pagodas with flexible joints. Essentially, this means that each floor of the building was able to move independently through earthquakes or storms. Though they were connected with brackets or “joints”, the stories were not connected with immovable framework. Additionally, these joints acted like a damper and helped to absorb some of the energy. Thus, during earthquakes each story of the building could move independently, without all of the stress going to the base. Additionally, many say it looks like a snake dancing as the different parts move, which is why many refer to it as a snake dance.
Flexibility has always been an essential part of earthquake resistance. However, as buildings were constructed higher and higher, more strategies were implemented to protect buildings. From cross bracing to base isolation, architects discovered many more ways to protect their buildings. There are many impressive examples of this. In Taiwan, the Taipei 101 building stands at a staggering 1667 feet (or 508 meters) and it was constructed incredibly close to a fault line (where tectonic plates meet, and earthquakes are most common) because of this, its earthquake-resistant design was essential in the blueprinting and construction stages. While there were numerous aspects to its design, the most noticeable is definitely the large yellow sphere spanning 4 stories of the building. From the 88th to the 92nd, the sphere is used as a TMD or tuned mass damper. Its purpose is to absorb and reduce shaking caused by the seismic waves. During an earthquake, the higher stories of the building will shake and the ball will shake in the opposing direction, countering the waves. Currently, Taipei 101 has already survived a strong earthquake (the 7.9 magnitude Sichuan earthquake of 2008) where the ball performed and kept the building safe.
While Taipei 101’s TMD is very obvious and visible, there are many others with a more subtle design that have been added to buildings worldwide. Especially when horizontal TMDs are used, the same counter-effect can be achieved without the obvious nature of a larger vertical TMD.
Oftentimes, constructors will build structures implementing a variety of ways to protect them from seismic waves. Base isolation is used often, as it can be added to many types of buildings with minimal interference to the structure’s other design elements (as opposed to a vertical TMD system like Taipei 101’s) The base isolation system works by construction the base of the building so that the base is not directly connected to the rest of the building. This reduces surface wave transmission and thus significantly decreases damage to the building itself. They also reduce friction which protects the base from further damage. One of the most known examples of base isolation is in Apple Park, California. Underground, its base contains 700 base isolators, each weighing nearly 1500 lbs.
In addition to protecting countless buildings from seismic waves, these designs also keep structures sturdier through typhoons, hurricanes, and any other events resulting in strong winds. These designs keep our urban world safe from the many dangers earth has to offer.
Sources
Cofer, Ashton. “earthquake-resistant construction | Britannica.” Encyclopedia Britannica, https://www.britannica.com/technology/earthquake-resistant-construction.
Science Channel. The Secret of the Pagoda's Earthquake Resistant Design.
Taylor, Douglas P. “Ancient construction is a model for earthquake-safe buildings.” NY Daily News, 8 November 2017, https://www.nydailynews.com/life-style/ancient-construction-model-earthquake-safe-buildings-article-1.3620347.
“Base Isolation Systems | Seismic Isolation.” Taylor Devices, https://www.taylordevices.com/base-isolation/.