Earthquakes are one of the most destructive forces of nature. Structures can suffer severe damage when an earthquake strikes. That's why, seismic loadings must be taken into account when designing structures, especially skyscrapers.
Let's roam around the world together and discover the top 5 earthquake-proof structures and learn how buildings can be designed to resist extreme seismic loadings.
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How do earthquakes happen?
As an engineer, in order to make solving a problem easier, it's important to understand what it is. So, what exactly is an earthquake and how do they happen?
Everyone knows about the existence of tectonic plates and how they influence the movement of the Earth's crust. Earthquakes happen when these tectonic plates move or collide with each other and release large amounts of energy. This is measured using the Richter scale.
The movement of these tectonic plates can generally be attributed to mantle convection, a phenomenon where warm mantle currents carry plates of lithosphere along like a conveyor belt. It may also be caused by the buoyant upwelling of the mantle at mid-ocean ridges. In this case, gravity causes the higher plate at the ridge to push away the lithosphere that lies further from the ridge. Another cause may be slab pull; it's a phenomenon where the older, colder plates sink at subduction zones. Subsequently, the cooler sinking plate pulls the rest of the warmer plate along behind it.
Professor Iain Stewart, a geologist from Plymouth University, explains how earthquakes happen and how they affect structures in this short clip. Knowing that waves radiate from the base of a structure throughout its whole body is essential in designing earthquake-resistant buildings.
One of the main elements of any earthquake-resistant building is base isolation. Let's take a quick look at what exactly this is.
What is base isolation?
The so-called base isolation is a technique developed by engineers to prevent - or at least minimize - the damage to buildings when exposed to earthquakes. These kinds of systems are used all over the world and are most prevalent in New Zealand, India, Japan, Italy, and the United States.
More traditional constructions, like fixed-base buildings, tend to be built directly onto the ground. While this is a sound practice for places that do not experience frequent earthquakes, it is highly advised against if not.
When an earthquake hits, the ground (and the building attached to it) moves with the quake's motion, causing massive damage to the building. To counteract this, most earthquake-proof buildings are isolated from the ground in some manner.
This usually involves using flexible bearings or pads known as base isolators. These kinds of systems move during a quake, but they move to counteract the forces generated by the movement of the building.
Base isolators work in a similar fashion to car suspension systems, which allow a vehicle to travel over rough ground by isolating the interior and absorbing the shock of uneven ground, without throwing the passengers inside around.
According to the Science Learning Hub, "during an earthquake, a building can move around 11 in (300 mm) or more relative to the ground. Therefore, the use of base isolation also means there must be a way for movement during an earthquake to be accommodated. This usually means a "rattle space" or "moat" has to be put in place around the building so that the building doesn’t crash into something nearby. Building services such as water, sewerage, and electrical all need to be designed to accommodate this movement without being damaged."
While base isolation can be a saving grace for many medium-rise brick or stone buildings, and can reinforce concrete ones, it is not suitable for all types of structures. Base isolators tend to have a limited ability to cope with tension.
This means that taller buildings have a very real risk of overturning or toppling during earthquakes if they have base isolators installed. For these kinds of buildings, other measures are required.
Base isolators are also not suitable for some sites due to other geotechnical and geographical reasons. For example, there may not be enough space to install them.
They also require hard soil, not soft soil, to operate at peak efficiency.
What are the different types of earthquakes?
A random fact about earthquakes: Did you know that there are about millions of earthquakes every single year? But don't worry, most of these are very small and virtually imperceptible.
Some of them, however, can be incredibly destructive, crumbling buildings and robbing people of their lives and livelihoods.
Earthquakes generally fall under one of a few distinct categories. These are:
- Tectonic earthquakes.
- Volcanic earthquakes.
- Collapse earthquakes.
- Explosion earthquakes.
Tectonic earthquakes occur at plate tectonic boundaries. Sometimes, friction between tectonic plates causes them to lock together and become unable to move. However, the rest of the plate carries on moving, which leads to increased pressure on the locked section. Eventually, the locked section succumbs to the pressure and shatters, the plates move rapidly, releasing energy and causing an earthquake.
Volcanic earthquakes are quakes that result whenever tectonic activity also causes volcanic activity.
Collapse earthquakes are minor earthquakes that occur whenever something like a mine or underground cavern collapses.
Explosive earthquakes are any form of an earthquake that is caused by a massive explosion, like a nuclear weapon detonation. Like collapse earthquakes, these tend to be very minor.
Earthquakes are also sometimes caused by human activity such as the injection of fluids into deep wells, the excavation of mines, and the filling of large reservoirs.
All earthquakes' relative strength is measured using the Richter Scale. According to Michigan Tech, typical ranges for various magnitudes of earthquakes include: -
|Magnitude||Earthquake Effects||Estimated Number|
|2.5 or less||Usually not felt, but can be recorded by a seismograph.||900,000|
|2.5 to 5.4||Often felt, but only causes minor damage.||30,000|
|5.5 to 6.0||Slight damage to buildings and other structures.||500|
|6.1 to 6.9||May cause a lot of damage in very populated areas.||100|
|7.0 to 7.9||Major earthquake. Serious damage.||20|
|8.0 or greater||Great earthquake. Can totally destroy communities near the epicenter.||One every 5 to 10 years|
If you want to learn more about what earthquakes are, Encyclopedia Britannica's entry on this subject is quite comprehensive.
What are some of the world's top earthquake-proof buildings?
And so, without further ado, here are some of the best earthquake-proof buildings from around the world. This list is far from exhaustive and is in no particular order.
1. Sabiha Gökçen International Airport is one of the world most earthquake-proof buildings
One of the major airports to serve the historical city of Istanbul, it also happens to be one of the world's most earthquake-proof buildings. Called Sabiha Gökçen, it is one of the two international airports in Istanbul, Turkey, which is located near the North Anatolian fault.
It was designed by the engineering firm Ove Arup to have 300 base isolator systems that can withstand an earthquake of up to a maximum of 8.0 Mw (moment magnitude). The base isolators can reduce lateral seismic loadings by 80%, which makes it one of the largest seismically isolated structures in the world.
One of the major features of the airport that makes it so earthquake-resistant is its so-called "triple friction pendulum device".
Architects Journal explains that "the whole terminal building sits on a platform that is, to a high degree, isolated from the ground below. This enabled the team to design the terminal almost as though it were situated in a non-seismic location, and to include features such as [structures with] large spans because the platform and pendulum devices mean that violent lateral ground movements will scarcely affect it."
The airport's triple friction pendulum bearing was manufactured by Earthquake Protection Systems (EPS). They use the principle of a basic pendulum to prolong a structure's isolation during serious earthquake events.
When an earthquake hits the structure, the airport's earthquake-proofing structures move with small pendulum motions. Earthquake-induced displacements occur primarily in the bearings, so lateral loads and movements transmitted to the structure are greatly reduced.
2. The Transamerica Pyramid can really take a pounding and keep standing
The Transamerica Pyramid is an iconic 1970s structure located in the Californian city of San Francisco, which sits closely beside the San Andreas and Hayward faults. In 1989, the Loma Prieta earthquake struck the area at a magnitude of 6.9 Mw which caused the top story of the structure to sway by almost one foot (30 cm) from side to side for more than a minute, but the building stood tall and undamaged.
This earthquake resistance feat can be attributed to the 52-foot-deep steel and concrete foundation that is designed to move with seismic loadings. Vertical and horizontal loadings are supported by a unique truss system above the first level, with interior frames extending up to the 45th level. The complex combination of these structural systems makes the building resistant to torsional movements and allows the absorption of large horizontal base shear forces.
3. The Burj Khalifa is also specially designed to resist earthquakes
This skyscraper doesn't really require any introduction. The Burj Khalifa is simply one of the most iconic supertall structures in the world. It also happens to be an earthquake-proof building!
The structure is composed of mechanical floors where outrigger walls connect the perimeter columns to the interior walling. By doing this, the perimeter columns are able to support the lateral resistance of the structure. The verticality of the columns also helps with carrying the gravitational loads.
As a result, the Burj Khalifa is exceptionally stiff in both lateral and torsional directions. A complex system of base and foundation design was derived by conducting extensive seismic and geotechnical studies.
4. Taipei 101 is another of the world's best earthquake-proof buildings
Taipei 101 is perhaps one of the most mesmerizing supertall skyscrapers in the world. The exterior design (by C.Y. Lee) was inspired by the phrase, "we climb in order to see further".
Putting aside the architecture, the mind-blowing fact about Taipei 101 is that it houses the biggest tuned mass damper (TMD) in the world! It's basically a giant metal ball that counteracts big transient loadings like wind and earthquakes to reduce the sway of the supertall tower.
The TMD is supported by hydraulic damper arms and bumper systems which function in the same way as a car's shock absorber. When large forces act upon the tower, the TMD sways in the opposite direction, bringing the entire building into equilibrium by damping out the transient forces using the ball's mass. How amazing is that?
This earthquake damper system is located between the 87th floor and the 92nd level.
5. Philippine Arena also happens to be an earthquake-resistant building
The Philippine Arena is the world's largest domed arena and is an amazing earthquake-proof structure. It is owned by the Christian group Iglesia Ni Cristo (INC) which commissioned this 55,000 seating capacity arena for their 100th anniversary three years ago on July 27, 2014.
It is also the centerpiece of the tourism enterprise zone called Ciudad De Victoria in Bulacan, Philippines. The arena was designed by Australian architecture firm Populous and the elite engineering firm Buro Happold.
The Philippine plate sits along the so-called Pacific Ring of Fire, home of the world's most notorious and active chain of earthquake fault lines. Previous earthquakes in the country have reached as much as 8.2 Mw, and have claimed thousands of lives. Seismic activities have also been responsible for volcanic eruptions and tsunamis in the region.
Philippine Arena's vast stadium roof, spanning 170m, was engineered to withstand severe transient loadings such as earthquakes, winds, and typhoons. During an earthquake, the lateral loads that generate throughout the structure can reach up to 40% of its mass.
Buro Happold cleverly responded with an independent base design for the entire structure, which means that the main structural body of the arena is isolated from its base and foundation. The gap between the main structure and base foundation system is composed of lead rubber bearings (LRB) which are a flexible arrangement of materials with high energy dissipation properties.
This allows the base and foundation system to freely move with the force of the earthquake, while the top structure remains stationary. This is truly an amazing earthquake engineering feat!
That's all for now folk.
So, the next time you visit one of these structures, take a moment to appreciate not only the architectural aesthetics but also the magnificent engineering feats they have to offer.
While there's no way of defeating the awesome power of nature, our engineers can tinker with the tools at hand to at least attempt to tame her. These, and other earthquake-resistant buildings around the world, are a testament to the ingenuity of man and the skill of the engineers behind their construction.