Earthquake-Resistant Building Technologies Earthquake is a concept that refers to the sudden release of strain energy in the Earth's crust and the resulting outward propagation of seismic waves from the earthquake source. When stresses in the Earth's crust exceed the strength of rock, an existing fault line or newly formed line begins to fracture. The point where an earthquake originates is called the earthquake center (hypocenter) and can be located several kilometers deep within the Earth. The point on the surface directly above the earthquake center is called the epicenter. The impact created by an earthquake is related to the soil hardness level in the area. The National Earthquake Hazards Reduction Program (NEHRP) has established six different soil classifications based on soil and rock type in the region and their shear wave velocity: Type A hard rock, Type B firm rock, Type C dense soil and soft rock, Type D stiff soil, Type E soft soil and Type F soils requiring site-specific investigation. Seismic waves move faster through hard soil than through soft soil; as waves pass from hard soil to soft soil, their amplitudes increase. Soft soil means larger waves and stronger amplification. Bedrock absorbs more wave energy than sandy soils, so buildings on solid rock are much less affected compared to those built on softer soils. When an earthquake occurs, shock waves propagate through the ground in all directions at short and rapid intervals. Although buildings are generally constructed to withstand vertical forces resulting from their weight and gravity, they cannot resist the horizontal forces generated by earthquakes. This horizontal movement shakes walls, columns, floors, beams, and the connectors that hold them together. The most dangerous type of earthquake is one that triggers horizontal movement, because tall buildings show better resistance to vertical loads than to horizontal ones. These ground movements can damage building foundations in just a few seconds. The difference in movement between the lower and upper portions of a building creates extreme stress, causing the load-bearing frame to fracture and subsequently the entire structure to collapse.

Earthquake-Resistant Materials

Ductility is a concept that describes a material's resistance to stress and vibration and includes the material's ability to withstand large deformations and stresses. Modern buildings are generally constructed with structural steel, which can be found in various forms and allows buildings to bend without breaking. Wood is also a ductile material due to its high strength relative to its light weight. Many scientists and engineers are developing new building materials that can better retain their shape. Innovations such as shape-memory alloys have the ability to withstand heavy pressures and return to their original shapes. Additionally, fiber-reinforced plastic wrapping made from various polymers can be wrapped around columns and provides up to 38 percent additional strength and ductility. Recently, engineers have also turned to natural elements to help strengthen buildings. The adhesive and strong fibers of mussels and the strength-to-size ratio of spider silk have notable potential in creating new structures. Bamboo and 3D-printed materials can also function as lightweight, interlocking tools that offer greater resistance to structures with unlimited forms.

Earthquake-Resistant Building Technologies

Shear walls are a useful building technology that can help redirect the direction of earthquake forces. Composed of multiple panels, these walls help a building maintain its shape while in motion. Shear walls help buildings remain stable by transferring lateral loads to the foundation, preventing the structure from bending or collapsing. While all shear walls serve the same purpose, the materials they are made from (such as concrete, steel and wood), their thickness, length and positioning vary depending on various factors in building construction and must comply with building codes. Shear walls are typically supported by diagonal bracing made of steel. These beams can support compression and tension by helping resist compressive and push forces. One of the most important reasons buildings collapse during earthquakes is foundation failure. When the foundation cannot withstand applied seismic stresses, it fails and causes the building to collapse. One method of resisting ground forces is a technique called base isolation, which raises the building's foundation off the ground. Base isolation involves building a structure on top of flexible blocks made of steel, rubber and lead. During an earthquake, when the base moves, the structure itself remains stationary while the isolators vibrate. This helps absorb seismic waves and effectively prevent them from traveling through the building. Retrofitting existing buildings to improve their seismic performance is just as important as using earthquake-resistant technologies. Engineers have demonstrated that adding base isolation systems to structures is both feasible and cost-effective. A more promising solution that is much easier to implement is a technology known as fiber-reinforced plastic wrapping or FRP. Manufacturers produce these wrappings by mixing carbon fibers with binder polymers such as epoxy, polyester and vinyl ester to create a lightweight but highly strong composite material. In strengthening applications, engineers wrap the material around the building's concrete support columns and then pump pressurized epoxy into the gap between the column and material. Even earthquake-damaged columns can be strengthened with carbon fiber wrapping. Another technology that helps buildings withstand earthquakes is dampers. Engineers typically install dampers on each floor of a building, with one end attached to a column and the other end attached to a beam. Each damper consists of a piston head that moves inside a cylinder filled with silicone oil. When an earthquake occurs, the horizontal movement of the building pushes the oil in each damper piston, converting the earthquake's mechanical energy into heat. Today, many high-rise buildings use core wall construction to increase seismic performance at lower cost. In this design, a reinforced concrete core passes through the center of the structure surrounding elevator entrances. For tall buildings, core walls can be quite important. While core wall construction helps buildings withstand earthquakes, it is not sufficient on its own. Researchers have found that fixed-base buildings with core walls can still experience significant inelastic deformations, large shear forces and damaging ground accelerations. For structures in earthquake zones, a rocking core wall combined with base isolation is considered a more effective solution. A rocking core wall rocks at ground level to prevent permanent deformation of the concrete in the wall. To perform this operation, engineers reinforce the bottom two floors of the building with steel and use post-tensioning throughout the height. In post-tensioning systems, steel beams are passed through the core wall. Tendons function as elastic straps that are tightly tensioned with hydraulic jacks to increase the tensile strength of the core wall.