EARTHQUAKE PROOF STRUCTURES

To earthquake-proof buildings, engineers work to reinforce the structure and counteract the potential or expected earthquake’s forces. Earthquakes release energy and as a result of the forces generated, it acts in such a way that it pushes on buildings from one direction thereby try to displace it. Therefore, the correct strategy to this displacing force involves having the building push the opposite way to counteract it.

Here are some of the methods used to help buildings withstand earthquakes.

1. Create a Flexible Foundation

One way to resist ground forces is to “lift” the building’s foundation above the earth through a method called base isolation. Base isolation involves constructing a building on top of flexible pads made of steel, rubber and lead. When the base moves during an earthquake, the isolators vibrate while the structure itself remains steady. This effectively helps to absorb seismic waves and prevent them from traveling through the building.

2. Counter Forces with Damping

If you’re familiar with shock absorbers used in cars, you might be surprised to learn that engineers also use a version of them in earthquake-resistant buildings. Similar to their use in cars, shock absorbers reduce the shockwaves magnitude and help reduce pressure on the building. This is accomplished in two ways: vibrational control devices and pendulum power.

2.1 Vibrational Control Devices

This method involves placing dampers at each level of a building between columns and beams. Each damper consists of piston heads inside a cylinder filled with silicone oil. When an earthquake occurs, the building transfers the vibrational energy into the pistons, which push against the oil. The energy is then transformed into heat, dissipating the force of the vibrations.

2.2 Pendulum Power

Another common damping method is pendulum power, used primarily in skyscrapers. To implement this, engineers suspend a large ball from steel cables that connect to a hydraulic system at the top of the building. When the building begins to sway, the ball acts as a pendulum and moves in the opposite direction to stabilize the building. Like damping, these features are tuned to match and counteract the building’s movement in the event of an earthquake.

3. Shield Buildings from Vibrations

Rather than just counteracting forces, researchers are experimenting with ways buildings can deflect and reroute the energy from earthquakes altogether. Dubbed the “seismic invisibility cloak,” this innovation involves creating a cloak of 100 concentric plastic and concrete rings and burying it at least 3 feet beneath the foundation of the building.

As seismic waves enter the rings, ease of travel forces them to move through to the outer rings. As a result, they are essentially channeled away from the building and dissipated into the ground.

4. Reinforce the Building’s Structure

To withstand collapse, buildings must redistribute forces that travel through them during a seismic event. Shear walls, cross braces, diaphragms and moment-resisting frames are central to reinforcing a building.

4.1 Shear walls

Shear walls are a useful building technology that can help transfer earthquake forces. Made of multiple panels, these walls help a building keep its shape during movement. 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.

 

4.2 Diaphragms.

Diaphragms are also a central part of a building’s structure. Consisting of the building’s floors, roof and the decks placed over them, diaphragms help remove tension from the floor and push forces to the building’s vertical structures.

4.3 Moment-resisting frames.

Moment-resisting frames provide additional flexibility in a building’s design. These structures are placed among a building’s joints and allow columns and beams to bend while the joints remain rigid. Thus, the building is able to resist the larger forces of an earthquake while still allowing designers the freedom to arrange building elements.

5.0 Earthquakes-Resistant Materials

While shock absorbers, pendulums and “invisibility cloaks” may help dispel the energy to an extent, the materials chosen for a building are equally responsible for its stability. The materials used for these purposes are steel and wood and in some cases innovative materials are employed specifically to suit the operating condition.

5.1 Steel and Wood

For a material to resist stress and vibration, it must have high ductility, which is the ability to undergo large deformations and tension. Modern buildings are often constructed with structural steel, a component that comes in a variety of shapes and allows buildings to bend without breaking. Wood is also a surprising ductile material due to its high strength relative to its lightweight structure.

5.2 Innovative Materials

Scientists and engineers are developing new building materials with even greater shape retention. Innovations like shape memory alloys have the ability to both endure heavy strain and revert to their original shape. Additionally, fiber-reinforced plastic wrap made by a variety of polymers can be wrapped around columns and provide up to 38% added strength and ductility.

Engineers are also turning to natural elements to help reinforce buildings. The sticky yet rigid fibers of mussels and the strength-to-size ratio of spider silk have promising capabilities in creating structures. Bamboo and 3D printed materials can also function as lightweight, interlocking structures with limitless forms that can potentially provide even greater resistance for buildings.

Over the years, engineers and scientists have devised multiple techniques to create effective earthquake-proof  buildings. However, as advanced as technology and materials are today, it is not always possible for buildings to completely withstand powerful earthquakes unscathed. Still, if a building is able to avoid collapse and save lives and communities, we can consider that a great success.

Top 5 Earthquake Resistant Structures around the World

1. Sabiha Gökçen International Airport

Sabiha Gökçen International Airport is one of airports to serve the historical city of Istanbul. It also happens to be one of the world’s most earthquake-proof buildings. it is one of the two international airports in Istanbul, Turkey, which is located near the North Anatolian fault line.

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”.

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. Transamerica Pyramid

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 torsional movements and allows the absorption of large horizontal base shear forces.

3. Burja Khalifa

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

Taipei 101 is another of the world’s best earthquake-proof buildings and 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.

5. Philippine Arena

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 is 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.

ETECHNOW

Sources:

(1)How Stuff Works 1, 2(2) REIDsteel (3) Rishabh Engineering (3) Seeker (4) Futurism

(5)VIATechnik(6)Interesting Engineering(7)Architizer(8)kcFED(9)National Geographic

(10) Civil + Structural Engineer (11)BigRentz