We have built magnificent cities and structures throughout history, but they have been destroyed by natural forces. One of the most damaging natural phenomena on earth is earthquakes, which send seismic waves causing buildings to collapse, people to die and enormous financial losses due to damage and restoration.
The National Earthquake Information Center estimates that there are typically 20.000 earthquakes each year, of which 16 are major disasters. On August 14, 2021, the 7,2 magnitude earthquake that shook southwest Haiti killed nearly 2.000 people. The collapse of buildings with residents inside contributed significantly to the destruction, as in past earthquakes, and made earthquake-resistant construction a necessity.
Engineers have increased the earthquake resistance of buildings by using new building designs and materials over the past few decades. Find out how modern buildings are made earthquake resistant by continuing reading or by scrolling to the infographic below.
Effects of Earthquakes on Buildings
Before looking at the characteristics of earthquake resistant buildings, it is vital to understand how earthquakes affect man-made structures. When an earthquake occurs, it causes shock waves to travel across the ground in short, rapid bursts that reach in all directions. Buildings can typically withstand the vertical forces produced by their weight and gravity, but not the side-to-side forces produced by earthquakes.
Walls, floors, columns, beams, and the fasteners that hold them together vibrate as a result of this horizontal movement. The upper and lower movements of the buildings are separated from each other, creating significant pressure on the support frame and ultimately causing the collapse of the entire structure.
Making a Building Earthquake Resistant
Engineers work to strengthen the structure and mitigate the effects of a potential earthquake when creating an earthquake resistant building. Since buildings are pushed in one direction by the energy released during earthquakes, the technique involves pushing the building in the opposite direction. Here are a few techniques to make structures more earthquake resistant.
1. Build an adaptive foundation
Base insulation is a technique used to “raise” the foundation of a building from the ground in order to withstand ground stresses. Base insulation requires building a structure over flexible steel, rubber and lead pads. When the foundation shakes during an earthquake, the isolators vibrate, but the building itself does not move. As a result, seismic vibrations are successfully absorbed and prevented from passing through the building.
2. Damping Forces in Counterforce
If you are familiar with the shock absorbers used in automobiles, you may be surprised to learn that engineers also use some form of shock absorbers in earthquake resistant buildings. Shock absorbers work similarly to cars: they reduce the force of shock waves and reduce stress on the structure. Pendulum power and vibration control devices are used to achieve this.
Devices to control vibration
This technique involves placing dampers between columns and beams at each level of a structure. Each damper consists of a cylinder and piston heads containing silicone oil. When an earthquake occurs, the vibration energy of the structure is transferred to the pistons pressing on the oil. The force of the vibrations is then dissipated as the energy is converted into heat.
Pendulum Force
Mostly used in skyscrapers, pendulum power is another typical damping technique. Engineers do this by hanging a large ball from steel cables attached to a hydraulic system at the top of the building.
The ball works like a pendulum and when it starts to swing, it swings in the opposite direction to stabilize the building. Like damping, these properties are adjusted to coincide with and resist the movement of the building during an earthquake.
3. Protect Structures From Vibration
Researchers are working on ways in which buildings can completely deflect and redirect energy from earthquakes rather than simply resisting them. Known as the "seismic invisibility cloak," the invention requires making a cloak of 100 concentric rings of plastic and concrete and buried at least three meters below the building's foundation.
Ease of movement forces seismic waves to pass into the outer rings as they enter the rings. As a result, the waves are effectively directed away from the structure and dispersed over the earth.
4. Strengthening the Structure of the Building
Buildings must redistribute the seismic forces that pass through them to withstand collapse. A building can be reinforced with shear walls, cross braces, diaphragms, and moment resisting frames.
Shear walls are a practical construction technique that can help transfer earthquake forces. Composed of several panels, these walls help a building maintain its shape as it moves. Shear walls are often supported by steel cross beams. These beams have the capacity to support both compression and tension, which helps them resist thrust and compressive stresses.
Another important component of a building's structure is its diaphragm. The diaphragms of the building's floors, roof and decks above them help to repel forces to the building's vertical supports and relieve ground tension.
Moment resistant frames give architects more freedom when designing a structure. These elements are placed between the joints in the building and allow the columns and beams to flex while the joints remain rigid. As a result, the building can withstand the greater forces of an earthquake while allowing architects to arrange building components as they see fit.
Earthquake Resistant Materials
Shock absorbers, pendulums, and "invisibility cloaks" can help dissipate energy to some extent, but the materials chosen for a building are also responsible for its stability.
Earthquake Prevention Effect of Wood and Steel Material
In order for a material to withstand stress and vibration, it must have high ductility (capacity to withstand significant deformations and stress). Structural steel, which is available in various shapes and allows buildings to bend without breaking, is frequently used in the construction of modern buildings. Wood is also an unexpectedly ductile material due to its remarkable strength compared to its lightweight structure.
Contemporary Materials to Prevent Earthquake Damage
Engineers and scientists are working to create new building materials that retain their shape even better. Shape memory alloys are an example of innovation that can withstand significant stress while returning to its original shape. In addition, columns can be covered with fiber-reinforced plastic wrap to offer up to 38% more strength and ductility. Such plastic wraps are produced from various polymers.
To strengthen buildings, engineers now resort to natural materials. Both the high strength-to-size ratio of spider silk and the inflexible but sticky fibers of mussels show promise for use in building materials. Bamboo and 3D-printed materials have the ability to further increase the resilience of a building, as well as being lightweight, interlocking structures with almost endless design options.
Engineers and scientists have developed a number of effective building methods that are earthquake resistant over the years. While today's materials and technology are highly sophisticated, it is not always possible for buildings to completely resist strong earthquakes without being damaged. However, if a building can prevent collapse and save the lives of people and communities, we can consider it a great success.
Source: bigrentz.com/blog/earthquake-proof-buildings
Günceleme: 06/02/2023 13:30
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