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Base Isolation Systems/Seismic Isolation - Coggle Diagram
Base Isolation Systems/Seismic Isolation
Who and When
Base isolator bearings were pioneered in New Zealand by Dr. Bill Robinson (scientist and seismic engineer) during the 1970s
What is base isolation/what is it made of
A technique developed to prevent or minimize damage to a building during an earthquake through the separation of the structure from its foundation
The technology is similar to a car's suspension system, which prevents occupants from excessive movement when driving over a bumpy road
The technology works best on stiffer soil and becomes less effective for infrastructure located close (about a few kilometres away) to a large fault since the system can become overwhelmed by the large and impulsive motion of earthquakes. In these cases, buildings with concrete walls can offer better protection.
Base isolators -- flexible bearings or pads -- made from layers of rubber and lead lay between the building's foundations and the structure above
These base isolators move and stretch under pressure and absorb an earthquake's impact by reducing swaying and shaking
The laminated layers of rubber and steel provide high axial stiffness and low lateral stiffness; the lead core provides energy dissipation to absorb seismic motion
Where are they used
It has been used in New Zealand, India, Japan, Italy and in the U.S. (city halls of Los Angeles, San Francisco, and Pasadena, and Apple's new headquarters in the Silicon Valley)
"The 10 Largest Base-Isolated Buildings in the World"
https://www.enr.com/articles/42366-the-10-largest-base-isolated-buildings-in-the-world
San Francisco City Hall
Around 40 buildings have base isolators in New Zealand
Why are they important/used/effective
The goal of base isolation is to reduce the transfer of earthquake forces from the foundations to the building above. It deflects and dissipates the seismic energy which lowers the natural frequency of the structure. This minimizes the displacement of the structure and protects its structural integrity
This reduces the need for extensive and intrusive strengthening concrete shear walls throughout the building
Researchers have found that base isolator systems allow a building to withstand an earthquake six times stronger than it would be able to without base isolation.
It significantly reduces damage of the infrastructure and risk of injury of the occupants within
Base isolation is very useful for hospitals, emergency centres and fire stations since they can still operate after an earthquake and readily assist patients
How do they work
Seismic waves cause the lateral movement of the foundation of the building. These waves are then transferred throughout the skeleton of the structure over time. The lateral movement of the skeleton results in stresses within the structure.
Each structure has its own natural frequency of oscillation which depends on factors such as stiffness, mass and height. The whole building will oscillate violently in sync with the earthquake frequency if the earthquake has natural frequencies with high energy that match the natural frequencies of the building. The building is less likely to be damaged if the natural frequency of the building does not match that of the earthquake.
A heavy and stiff structure will not sway as much as light and slender structures. Skyscrapers are tall and slender and have low natural frequencies and big deflections.
Base isolators work on this principle; It reduces the stiffness of the structure (allows a displacement in all directions) and thereby reduce its natural frequency. As a result, the building will respond to the seismic activity in a rigid manner rather than resonating with its frequency
Reference links (not cited yet)
https://www.sciencelearn.org.nz/resources/345-dr-bill-robinson-1938-2011
https://www.taylordevices.com/base-isolation/
https://www.sciencelearn.org.nz/resources/1022-base-isolation-and-seismic-dampers
https://happho.com/base-isolation-techniques-applications-advantages-disadvantages/
https://www.quanser.com/blog/base-isolation-structural-control/
https://www.parliament.nz/en/visit-and-learn/how-parliament-works/fact-sheets/earth-move/
https://www.physicscentral.com/experiment/physicsathome/baseisolatedbuilding.cfm
Videos
https://www.youtube.com/watch?v=BXqRDUWadGM&list=PLn_OnfjlkoeFd6SCqEP9OMGR4fdgn7VmE&index=3&ab_channel=DynamicIsolationSystems%2CInc
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https://youtu.be/zLtGR46FUss
https://youtu.be/fw0rgJUtXiM
