Seismic Base Isolation Technique for Building Earthquake Resistance




It is easiest to see the principle at work by referring directly to the most widely used of these advanced techniques, known as base isolation. A base isolated structure is supported by a series of bearing pads, which are placed between the buildings and building foundation.

Base Isolation Technique

Base Isolation Technique

The concept of base isolation is explained through an example building resting on frictionless rollers. When the ground shakes, the rollers freely roll, but the building above does not move. Thus, no force is transferred to the building due to the shaking of the ground; simply, the building does not experience the earthquake.

Now, if the same building is rested on the flexible pads that offer resistance against lateral movements (fig 1b), then some effect of the ground shaking will be transferred to the building above. If the flexible pads are properly chosen, the forces induced by ground shaking can be a few times smaller than that experienced by the building built directly on ground, namely a fixed base building (fig 1c). The flexible pads are called base-isolators, whereas the structures protected by means of these devices are called base-isolated buildings. The main feature of the base isolation technology is that it introduces flexibility in the structure.

As a result, a robust medium-rise masonry or reinforced concrete building becomes extremely flexible. The isolators are often designed, to absorb energy and thus add damping to the system. This helps in further reducing the seismic response of the building. Many of the base isolators look like large rubber pads, although there are other types that are based on sliding of one part of the building relative to other. Also, base isolation is not suitable for all buildings. Mostly low to medium rise buildings rested on hard soil underneath; high-rise buildings or buildings rested on soft soil are not suitable for base isolation.

Concept of Base Isolation

Concept of Base Isolation

Lead-rubber bearings are the frequently-used types of base isolation bearings. A lead rubber bearing is made from layers of rubber sandwiched together with layers of steel. In the middle of the solid lead “plug”. On top and bottom, the bearing is fitted with steel plates which are used to attach the bearing to the building and foundation. The bearing is very stiff and strong in the vertical direction, but flexible in the horizontal direction.

How it Works

To get a basic idea of how base isolation works, first examine the above diagram. This shows an earthquake acting on base isolated building and a conventional, fixed-base, building. As a result of an earthquake, the ground beneath each building begins to move. . Each building responds with movement which tends towards the right. The buildings displacement in the direction opposite the ground motion is actually due to inertia. The inertia forces acting on a building are the most important of all those generated during an earthquake.

In addition to displacing towards right, the un-isolated building is also shown to be changing its shape from a rectangle to a parallelogram. We say that the building is deforming. The primary cause of earthquake damage to buildings is the deformation which the building undergoes as a result of the inertial forces upon it.

Response of Base Isolated Buildings

The base-isolated building retains its original, rectangular shape. The base isolated building itself escapes the deformation and damage-which implies that the inertial forces acting on the base isolated building have been reduced. Experiments and observations of base-isolated buildings in earthquakes to as little as ¼ of the acceleration of comparable fixed-base buildings.

Acceleration is decreased because the base isolation system lengthens a buildings period of vibration, the time it takes for a building to rock back and forth and then back again. And in general, structures with longer periods of vibration tend to reduce acceleration, while those with shorter periods tend to increase or amplify acceleration.

Spherical Sliding Base Isolation

Spherical Sliding Base Isolation

Spherical Sliding Base Isolation

Spherical sliding isolation systems are another type of base isolation. The building is supported by bearing pads that have a curved surface and low friction. During an earthquake the building is free to slide on the bearings. Since the bearings have a curved surface, the building slides both horizontally and vertically. The forces needed to move the building upwards limits the horizontal or lateral forces which would otherwise cause building deformations. Also by adjusting the radius of the bearings curved surface, this property can be used to design bearings that also lengthen the buildings period of vibration

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  1. #1 by janki on July 17, 2010 - 8:28 am

    thanks so much for this explanation

    • #2 by nandakishore on January 23, 2011 - 1:50 am

      very valuable information for the emerging civil engineers

  2. #3 by PAUL CURA on November 10, 2010 - 12:23 am

    THANKS A LOT..IT REALLY HELPED ME ON MY WORKSHOP PRESENTATION REGARDING BASE ISOLATION..

  3. #4 by HECTOR VALENCIA on December 10, 2010 - 3:11 pm

    I am the inventor of the Seismic Filter (SF), a device that isolates structures from ground displacements provoked by earthquakes. It achieves this task up to a point that their occupants will hardly become aware of the occurrence of a tremor, no matter its displacements, magnitude, duration or ground velocities. The tests carried out at UCSD demonstrate the veracity of this statement.
    Under the direction of André Filiatrault PhD – now Deputy Director of Multidisciplinary Center for Earthquake Engineering Research – a test program was inspired from the “Guidelines for the Testing of Seismic Isolation and Energy Dissipating Devices” prepared by the Highway Innovative Technology Evaluation Center (HITEC 1996). The tests were conducted under three different confining pressures: 1400, 3500 and 6000psi. For each confining pressure, three different types of tests were conducted:
    • 1 performance benchmark.
    • 11 frequency dependency
    • 6 earthquake-aftershock simulation (Mexico’85(1), Northridge’94(2), Saguenay’88) (3)
    (1) 16C temperature gain after 3 min. simulated ground displacements
    (2) Peak relative velocity  120cms/sec.; 1.7G peak acceleration
    (3) Earthquakes chosen as representatives of soft, intermediate and hard grounds

    After 33 frequency tests plus 27 accumulated minutes of earthquake simulations, Dr. Filiatrault concluded in his DYNAMIC CHARACTERIZATION OF A SEISMIC FILTER Report: ”For the three confining pressures considered in the test, the behavior of the seismic filter is repeatable, stable and nearly identical in tension-compression. The hysteresis loops are nearly rectangular indicating a coulomb-type frictional response. The static coefficient of friction varied from 0.08 to 0.025. The kinematic coefficient friction varied from 0.003 to 0.013”.
    Afterwards, Jose Restrepo PhD, Director of Operations Charles Lee Powell Structural Laboratories at UCSD, used Seismic Filters as “sliders” (they allow relative displacements structure-foundation) in the tests of a three story prefab building erected on the Englekirk shake table (2nd largest in the world). The structure was much wider than the shake table and the overhanging sides were supported by SF. The results, as far as the SF was concerned, were spectacular.

    Presently, the Seismic Filter comprises two different materials: steel and plastic. Even though, the comparative selling price between my invention and those of the competitors are extremely in favor of mine, it still is not economically desirable for its use in small one or two story commonly built houses. Therefore, I am looking to overcome this hurdle and give most people affordable earthquake isolation for any type or size of construction: houses, buildings, structures, etc. This endeavor can become possible with the implementation of plastic or carbon-fiber injected into molds to replace the machined steel and plastic components. The minimal requirements for such a product are:
    1. Lubricated Dynamic Friction Coefficient 10,000psi
    3. Shear strength > 6,000psi
    4. Relatively flexible
    5. Non-combustible
    6. High temperature resistant
    In my prototypes, I have used Nylamid XL in cylinder shape that I have machined, but I desire to know if you carry a product, plastic or carbon fiber, of similar-superior properties of inject able type or are willing to manufacture it.
    I will also greatly appreciate it if you communicate to me if your company would be interested in becoming directly involved with my invention in this sure to become world-wide market.

    • #5 by Alan camacho on April 29, 2012 - 1:47 pm

      Dear Mr Valencia: Im working on a proposal involving the building a single level masonry structure of aprox. 40,000 sq. feet, with a basement of aprox. 30,000 sq. feet on hard soil, and would like to know if you have come up with a SF device suitable for this application and the costs associated with it. Please kindly reply to my e-mail address.

  4. #6 by Malcolm Bland on December 23, 2010 - 10:20 am

    Is there a list of products or manufacturers for seismic isolation pads?

  5. #7 by Cookies on December 30, 2010 - 3:42 pm

    this really explained things for me on my science project and gave a GREAT deal of info

  6. #8 by Mayur on January 4, 2011 - 11:56 pm

    Sir,
    We are planning for multistoried hospital building and for that we may decide the use of bearing for earthquake resistance. So, how much it cost and which company do the work? If possible please give me some idea about it and send me some prospects also.
    Thanking you,
    With regards,
    Mayur Bhavsar.

    • #9 by Lindsay R Jones, Pd D on July 11, 2011 - 3:19 pm

      I am in the base isolation business and can help you. Send me information about your hospital project and i will reply with the information you are looking for

      • #10 by sepide on December 1, 2012 - 1:42 am

        I am a student of civil eng & now looking for info about oil tanks’s base isolation,So if you now:
        what kinds of base isolation exist?when we use which of them? how much they cost?or any thing else please share your info or experience with me
        and help me
        thanks a lot

  7. #11 by pankaj on January 14, 2011 - 9:24 am

    I am studant of Mtech

  8. #12 by Rajendra Acharya on January 23, 2011 - 8:05 pm

    Sir,
    I’m interested in the fields of seismic base isolation

  9. #13 by Ethan on May 19, 2011 - 5:05 pm

    I am a student at Tauranga boys college in New Zealand and for this inquiry I am researching base isolators. I was hoping that you could provide some information on the cost of base isolators thanks.

    • #14 by sepide on December 1, 2012 - 1:55 am

      Do you any thing about Robinsons company( a new zealand company that work in this field)?
      (I am a student of civil eng & looking for info about oil tanks’s base isolation

      thanks a lot )

    • #15 by pawankumar on April 9, 2013 - 9:21 pm

      I am a student at DCE/ DELHI INDIA and for this inquiry I am researching base isolators. I was hoping that you could provide some information on the cost of base isolators thanks.

  10. #16 by priya.punpun on July 4, 2011 - 10:27 pm

    it.s very useful information about base isolator which i got fully satisfication and

  11. #17 by surya on August 2, 2011 - 11:59 am

    im a mtech student in structures..hey itz really gud..very much useful while giving the presentation on base isolation..

  12. #18 by monisha on August 3, 2011 - 10:10 am

    thanks a lot 4 providing those useful info’s….

  13. #19 by hermy & em on August 31, 2011 - 5:23 pm

    Thanks, this really helped for our science assingment.

  14. #20 by Alok Sarkar,C.E., M.S., B.Sc(Civil) on September 23, 2011 - 12:12 am

    well written article. I think this will be helpful to professionals and non-professionals alike. Thanks!

  15. #21 by Mayur on September 26, 2011 - 5:25 am

    Hello sir, I am a student of City University, London studying civil engineering and need some help in Base Isolation, as I am making a project ob it.

  16. #22 by Tejan Patel on January 27, 2012 - 6:31 am

    sir, i want design of a building with base isolation provided

  17. #23 by dev on March 20, 2012 - 7:08 pm

    Hi I read your article ans is really help full and I am actually stimulating it has my project some of points I am getting confuse are as follow:
    1) hwo much weight one assume on bearings due to building
    2) what is magnitude of force due to earthquke
    3) as mention lead rubber bearings are use, how can I make them on stimulation and how canI get properties for this material.
    I am using hyermesh
    please let me know asap
    thanks

  18. #24 by martin morning on July 31, 2012 - 7:40 pm

    Thanks a lot this helped me in history class. :)

  19. #25 by martin morning on July 31, 2012 - 7:44 pm

    Thanks you have a lot of good info on title waves and volcanoes im so gonna do good in my upcoming test. :) :) :)

  20. #26 by lorraine san pedro on September 25, 2012 - 9:58 pm

    hi. good day.. i am a civil eng’g student and now doing a research about base isolation of a low rise building.. but for now i am not yet sure of what i am going to do.. can you suggest something new about it that i can workout for.. thankyou..

  21. #27 by civil on November 2, 2012 - 9:35 am

    hi dear
    i worked at base isolation system and write article about it but, i dont know that, how verify my model with articles concern about these topic?please guide me for verifying.

  22. #28 by k.Lakshmanan on January 11, 2013 - 10:43 pm

    I am a final yr civil student I am intrested in base isolating tech. I want to do my project in base isolation so I need some ideas and information related to that so please send any information you know ………thanking u

  23. #29 by tjf on January 20, 2013 - 12:18 am

    :) :)

  24. #30 by A.LEONARD POGSON on March 1, 2013 - 2:54 am

    I AM INTERETESTED IN HECTOR VALECIAS
    WORKS AS RELATED TO LIQUID NATURAL GAS TANKS IN HIGH SEISMIC AREAS
    ALP

  25. #31 by Oral Oh on April 17, 2013 - 1:47 am

    Was the Hagia Sofia, Istanbul one of the earliest buildings with base isolators made of lead?

  26. #32 by Larry Bowlus on April 21, 2013 - 2:22 pm

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    3. It is usually made of standard plate steel, but other materials will work.
    4. This base isolation solution is not complex, it has very few parts.
    5. Our device will scale up in size and strength to handle large structures.
    6. The engineering needed to design and deploy is straight forward.
    7. Our device will handle larger ground displacements of five to six feet, more than any prior device.
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  27. #33 by Swati on April 30, 2013 - 3:37 am

    Case study of base isolation

(will not be published)