Earthquake-Resistant Building Technologies

Throughout history, mankind has built impressive structures and cities whose durability could only be tested by the forces of nature. Among these natural forces, the most dangerous is undoubtedly the earthquake. Seismic waves in the ground can destroy buildings and claim lives. The devastation brought by earthquakes also results in enormous financial costs. According to the U.S. National Earthquake Information Center, an average of 20,000 earthquakes occur each year; although the majority are of low magnitude and go unnoticed, those that cause major disasters continue to claim lives in any corner of the world. For example, in September 2017, a magnitude 7.1 earthquake shook Mexico's capital and killed approximately 230 people. As with other earthquakes, the damage came not from the earthquake itself, but from the collapse of buildings with the people inside them. Of course, this reality makes earthquake-resistant buildings essential. Over the past several decades, engineers have introduced new designs and construction materials to better equip buildings to withstand earthquakes. But first, it is important to understand how earthquakes affect man-made structures. When an earthquake occurs, short shock waves are created at different intervals across the ground. Buildings are generally designed to carry vertical forces, that is, forces resulting from their own weight and gravity, so they struggle to resist lateral forces emanating from earthquakes. This lateral load shakes walls, floors, columns, beams, and the connectors holding them together. The difference in movement between the top and bottom of buildings can apply excessive pressure, causing the support frame to break and the entire structure to collapse. How Can an Earthquake-Protected Structure Be Built? To design earthquake-resistant buildings, engineers must strengthen the structure and prevent earthquake forces. Since earthquakes release energy by pushing a building in one direction, the strategy is to push the building in the opposite direction. In this article, we have tried to examine some of the methods used to help buildings withstand earthquakes.

Flexible Foundation

One way to resist ground forces is to "lift" the building's foundation off the ground. Base isolation involves building a structure on flexible pads made of steel, rubber, and lead. When the base moves during an earthquake, the isolators vibrate and the structure itself remains stationary. This effectively helps absorb seismic waves and prevents these waves from traveling through the building.

Damped Counter Forces

Almost everyone knows that vehicles have shock absorbers, but most people do not know that they are also used to create earthquake-resistant buildings. Similar to their use in automobiles, shock absorbers reduce the force of shock waves and help buildings slow down. This is accomplished in two ways: vibration control devices and pendulum dampers.

Vibration Control Devices

The first method involves placing dampers between a column and beam at each level of a building. Each damper consists of piston heads inside a cylinder filled with silicone oil. When an earthquake occurs, the building transfers vibration energy to the pistons, pushing against the oil. The energy is converted to heat, distributing the force of the vibrations.

Pendulum Power

Another damping method is pendulum power, used primarily in skyscrapers. Engineers suspend a large sphere with steel cables connected to a hydraulic system at the top of the building. When the building begins to sway, the sphere acts as a pendulum and moves in the opposite direction to balance the motion. Like damping, these features are tuned to match and balance the building's frequency during an earthquake.

Shielding Buildings from Vibrations

Researchers are testing methods beyond counter forces that would allow buildings to deflect and redirect energy from earthquakes. This innovation, called a "seismic invisibility cloak," involves creating a cloak of 100 concentric plastic and concrete rings and burying it beneath the building's foundation. When seismic waves reach these rings, they are forced to pass through the outer rings. As a result, they are essentially channeled away from the building and distributed to the plates in the ground.

Strengthening the Building's Structure

To withstand destruction, buildings must redistribute forces passing through them during a seismic event. Shear walls, braces, diaphragms, and moment-resisting frames are central to strengthening a building. Shear walls are a useful building technology that helps transfer earthquake forces. Made of panels, these walls help a building maintain its shape during movement. Shear walls are typically supported by diagonal cross-braces. These steel beams have the property of supporting compression and tension, which helps prevent pressure and push forces back to the foundation. Diaphragms are a central part of a building's structure. Diaphragms, which are horizontal surfaces consisting of the building's floors, roof, and decks, take the stress from the ground and direct this force to the building's vertical structures. Moment-resisting frames provide more flexibility in a building's design. This structure is placed between additional locations in the building and allows columns and beams to bend while joints remain rigid. In this way, the building can resist greater forces from earthquakes while providing designers with more freedom in arranging structural elements.

Earthquake-Resistant Materials

While shock absorbers, pendulums, and "invisibility cloaks" can help dissipate energy to a certain degree, the materials used in a building are equally responsible for its stability.

Steel and Wood

For a construction material to withstand stress and vibration, it must have high ductility - the ability to undergo large deformations and strain. Modern buildings are often constructed with structural steel - a steel component that comes in various shapes allowing buildings to bend without breaking. Wood is a surprisingly ductile material due to its high strength relative to its light weight.

Innovative Materials

Scientists and engineers are developing new building materials with even better shape-retention properties. Innovations like shape-memory alloys can both withstand heavy strain and return to their original shapes, while fiber-reinforced plastics made from various polymers can be wrapped around columns and provide 38% more strength and ductility. Engineers are also turning to natural elements. Mussel fibers and spider silk, which are sticky yet strong, have promising potential in building structures due to their strength-to-length ratio. Bamboo and 3D-printed materials can also function as lightweight, interlocking structures in unlimited shapes that could potentially provide greater resistance for buildings. Prepared by: B.Serhat Cengiz Sources: • https://science.howstuffworks.com/engineering/structural/earthquake-resistant-buildings.htm • http://www.reidsteel.com/steel-buildings/resilient-steel-structures/earthquake-resistant-building/ • https://www.rishabheng.com/blog/earthquake-resistance-design-techniques-for-civil-structure/ • https://www.viatechnik.com/science-behind-earthquake-proof-buildings/ • https://interestingengineering.com/top-5-earthquake-resistant-structures-around-world • https://tommytoy.typepad.com/.a/6a0133f3a4072c970b01538e0889f1970b-600wi • https://www.kansascityfed.org/publications/research/oke/articles/2016/economic-damage-large-earthquakes • https://www.nationalgeographic.com/environment/natural-disasters/earthquakes/ • https://www.bigrentz.com/blog/earthquake-proof-buildings