Most buildings can handle up-and-down forces, but fail in an earthquake because of horizontal forces that stress walls, support frames and connections. Earthquake resistant structures redistribute these forces through shear walls, diaphragms and bracings.
Steel offers several advantages in earthquake proofing, including its ability to bend and resist fractures. Wood’s ductility boosts its resilience as well.
Steel
Earthquakes are one of nature’s most destructive forces. Their ground-shaking vibrations can cause structural collapse in buildings that are not designed to resist them. Engineers and builders continue to seek ways to strengthen the resilience of structures in seismic zones, ensuring safety and stability for residents and workers.
Steel is a key material in earthquake resistant building designs. Its high strength-to-weight ratio makes it possible to construct stronger, lighter buildings that can withstand more force. Steel is also highly ductile, meaning it can bend and dissipate the energy of an earthquake without losing its load-carrying capacity. In turn, this reduces the strain on a building and lowers the risk of structural failure.
In addition to its exceptional strength, steel offers a number of other advantages for seismic resistance. For example, the fasteners used in cold-formed steel framing remain secure during and after an earthquake, despite being subjected to substantial stress. Furthermore, connections made with steel can withstand lateral forces up to seven times more than those secured in wood construction.
Builders can use steel in several ways to make a structure more resilient against an earthquake, including cross braces that frame the exterior of a building in an x-shaped pattern and transfer the force of seismic waves back to the ground, rather than allowing the building to take the hit. Shear walls are another way to add rigidity to a building frame and improve its resistance against swaying or horizontal movements caused by an earthquake.
Wood
Wood has long been a highly resilient building material. From the 8th-century Japanese temples to 11th-century Norwegian stave churches, wooden buildings of all shapes and sizes have proven to withstand earthquakes and other natural disasters. Today, research continues to prove that light-frame wood and mass timber construction can provide high levels of resilience, seismic performance and wind resistance in structures designed to meet prescriptive code requirements.
The structural configuration and redundancy of wood buildings make them more resistant to damaging forces in a quake than those of concrete structures. Because of its low weight, wood is able to disperse force through a network of shear walls and plywood or oriented strand board (OSB) diaphragms. In addition, wood’s ductility – its ability to bend and disperse force without breaking – allows for buildings to flex during an earthquake and resist lateral loads.
Engineers are now testing mass timber, which consists of layers of wood bonded together, to see how it performs in taller, seismically resilient buildings. The NHERI TallWood project, for example, has tested a 10-story mass timber structure at one of the largest shake tables in the world. Its results have demonstrated that buildings constructed of this material are capable of surviving earthquakes at a rate 1.5 times greater than comparable concrete buildings. This type of building can help increase the resilience of key facilities such as fire halls, police and rescue stations and schools to ensure they are able to continue providing services after a natural disaster.
Shear Walls
Shear walls resist lateral forces that cause buildings and structures to shake. They distribute these forces evenly, preventing them from concentrating on one part of the structure. They also help prevent the building from collapsing during an earthquake.
Steel plate shear walls are often used to withstand earthquakes and other large lateral forces. They typically have a plane or flanged section and can be combined with other structural elements like columns to provide a stronger system. Steel shear walls are lighter than concrete shear walls, reducing the amount of force they need to withstand. They can also dissipate energy during an earthquake, making them safer for people inside the building.
Most houses and buildings in seismic zones require exterior shear walls. Larger houses, high-rise buildings, and skyscrapers may need interior shear walls as well. Interior shear walls can come in the form of core walls or box-shaped columns strategically placed in areas like stairwells and elevators. They can be constructed in either wood or steel, depending on the needs of the structure.
Most shear walls in wooden buildings are made by attaching sheathing (plywood or oriented strand board [OSB]) to frames. Builders fasten these sheathings with nails sized and spaced according to an engineer’s specifications. They also use metal connectors to connect the sheathing to framing and other structural elements.
Architectural Metal
A variety of innovative steel-based designs and reinforcements can make buildings more resistant to seismic forces. These include shear walls, cross braces, and diaphragms that redirect seismic forces away from weaker parts of the structure. Additionally, buildings can be constructed on a base of springs or runners to separate them from the ground and absorb seismic energy from below.
A building’s structural integrity can be boosted by using shear walls and cross braces, which are essentially an X-shaped frame around the outside of a structure. This can prevent the structure from collapsing during an earthquake by transferring seismic waves to the ground, rather than letting the building take the full force of the wave.
In addition to utilizing shear walls and other design techniques, builders can use steel to reinforce buildings with base isolation systems. This type of construction involves placing a building on top of shock-absorbing materials, like massive blocks of rubber, to ensure that the foundations can move independently of the rest of the structure during an earthquake.
Metals used in architecture can also be strengthened through a heat treatment process, which can increase their strength and durability. They can also be made more resilient by incorporating an element called shape memory alloys. These are special types of metal that can retain their original shapes even when under a lot of pressure.