Base Isolation and Seismic Dampers: How Skyscrapers Dance with Earthquakes
All buildings are designed to sway and absorb movement. Despite what many think, buildings are not rigid structures, they are not stable; instead they move, everyday, by such a small margin that it is unnoticeable by us; much like a skilled dancer responding to a partner's rhythm, modern skyscrapers are designed to sway, glide, and absorb energy.This property of buildings swaying is used not only as a preventive measure against earthquakes but is also used in balancing out the everyday forces a building in use experiences. The two main technologies that make this possible are base isolation systems and seismic dampers. Together, they allow buildings to work with earthquake forces rather than against them.
There are many ways to battle against the earthquake without actually going against nature itself. But first we need to understand how the forces in a building work. A building primarily consists of a concrete core and supporting columns reinforced with steel. This concrete core acts as the main support for the whole building and channels all the forces into the ground. The building is designed in such a way that even if a part of the structure is damaged, the forces will flow around it and the building will not collapse in on itself.
An elegant solution is base isolation. This process involves inserting special flexible bearings between the structure and the ground instead of direct connection. So, when an earthquake hits, the flexible bearings absorb the movement of the earthquake and reduce the impact on the building. Another solution is the seismic dampers. Where base isolation is like a shock absorber, seismic dampers function as brakes. When a skyscraper moves during an earthquake, seismic dampers absorb and dissipate kinetic energy that would otherwise continue to move throughout the structure.
There are two types of seismic dampers; hydraulic damper and tuned mass damper. The hydraulic damper uses the principle of converting fluid into energy. A large piston pushes through a fluid filled cylinder, causing compression and turning the compression into forces which reduces the sway of the building. The other type of seismic damper is the tuned mass damper which uses the principle of weights to counteract the movement of the building. A huge weight, in the form of a pendulum or a ball is hung from the top and when the structure begins to sway, the mass moves in the opposite direction, effectively cancelling the net movement. This type of seismic damper is used in almost all the skyscrapers built today. A great and successful example is the Tepei 101 which has a huge pendulum made of steel and weighing about 660 tonnes.
During an earthquake the ground shakes and so the building. The building sways more than its normal movement. The installation of the metal pendulum, weighing 660 tonnes and made up of steel, in the Tepei 101 was completed in 2004. This metal ball is the largest among all the skyscrapers. In August 2015, when a typhoon swept the city of Taiwan off its feet, with winds blowing at least 170km/hr but the Tepei remained standing as the sway of the building was balanced out by the metal pendulum which swung the other way. This typhoon recorded the largest sway of the pendulum; about 1m.
References:
https://www.iitk.ac.in/nicee/EQTips/EQTip24.pdf
https://www.sciencelearn.org.nz/resources/1022-base-isolation-and-seismic-dampers Agarwal, R. (2020). Built. HarperCollins India.
https://www.taipei-101.com.tw/en/observatory/feature