Seismic Isolation Experiment

[chosunboy02]

Dear readers,
I have a project idea that involves experimentation with seismic isolators.
First I will build a basic foundation of the building, similar to this one: http://www.dis-inc.com/seismic_isolation.html (scroll down and there is an earthquake simulation of the building. I will create the one on the right).
Then I was thinking about building a layer of "earth" and place it above the foundation.
Here's my rudimentary idea of "earth": place ball bearings between two pieces of wooden block, so one piece would shift to one direction, while the other piece shifts to the opposite direction.
In my hypothesis, transfering seismic wave to another layer of "earth" would limit the impact of the waves, since "earth" will have a limited range of movement.
After placing the "earth" above the foundation, I will place the same foundation above the "earth" and see if adding another layer of "earth" would reduce the impact of seismic waves on the building.

My two main questions are: "Is this feasible?" and "Has this been done before?"

[ChrisG]

Hi chosunboy02,
Welcome to the Ask an Expert forums. Congrats on what sounds like a very promising start to your project.
I don't yet understand your plan well enough to say whether anyone has done it before, but that should not be a major obstacle anyway. You can always adapt your experiment to complement what has already been done.
By "earth" do you mean soil? I don't understand the idea of using ball bearings in place of "earth." It sounds as though you are planning to do something similar to what is shown on the animation on the left on that web page you gave, as opposed to the one on the right.

Chris

[chosunboy02]

Yes, I apologize for my mistake. I meant the animation on the right.
And when I say earth, I mean I will create a structure that will act like the earth.
Let's take it step by step:
1. Take two pieces of wooden block (5ft in length)
2. Place ball bearings between the wooden blocks

Now that's the "earth." I will construct it in a way, when a lateral forces is applied
one piece of wood will shift to one side while the other piece shifts to the opposite side.

During an earthquake, the earth experiences an lateral movement. I am trying to minimize that lateral movement by transferring the seismic wave to my "earth."
I hope my explanation is clear enough for you to understand.

[tdaly]

Correct me if I am wrong, but I think that when you are talking about "earth" you are referring to the shaking of the Earth that occurs during an earthquake. I think that what you are describing would be better termed a "shake table". A shake table is something that simulates the shaking that occurs during an earthquake. I think that for your purposes, the design you have outlined would be acceptable. You are not going to be able to reproduce the kinds of waves that cause the shaking that happens during an earthquake (e.g. p-waves, s-waves, and surface waves; if you don't know what these are then take a look at this site: http://en.wikipedia.org/wiki/Seismic_wave) but I think that for your experiment you can show the effectiveness of your seismic isolation method with the general design you have outlined. I would add that you might want to think about putting resistance (something like rubber bands) that wrap around the two boards that sandwich the ball bearings between them. If you put four rubber bands (one on each side) on, you will be able to give the top board a shake and then it will continue to shake back and forth because of the rubber bands. You might also think about using small rubber balls (like bouncy balls) of the same size instead of ball bearings. The wood pieces will not slide as much on the rubber balls and so if you combine the rubber bands with the rubber balls, you will get more shaking and less sliding.

This Project Idea outlines the design very well. Take a look at it; I think it will help you greatly: https://www.sciencebuddies.org/science- ... p013.shtml

You will need to be careful, however to make sure that your shake table is not the same as your foundation. If all you are doing is placing a second set of ball bearings with a board on top of them to represent your seismically isolated foundation, you need to really think about whether that experiment will answer your question. The basic idea is that if you use the same thing for your shake table as you do for your foundation, you haven't really done much. If this doesn't make sense or you don't understand why this might be a problem, post back and we'll discuss it further. We can help you find ways to make your project more meaningful and accurate.

[chosunboy02]

I do know what a shake table is, but that is not what I am trying to describe.
It is really difficult to exlain what it is without showing you the picture.
I can send you a picture of my model if you don't mind giving me your email address.

[Craig_Bridge]

I do know what a shake table is

Then you need to do some literature search and reading on shake tables. In order to evaluate any given proposed isolation experiment scientifically, you are going to have to utilize some experimental test equipment. Shake tables are a common test tool for this.

Ball bearings have been utilized on some small structures that have a large footprint compared to the height. The problem with ball bearings is they won't provide any tension isolation. If you don't understand tension, compression, and shear forces, you need to do some reading on them.

Damped springs are more commonly used as isolators because they handle compression, tension, and shear forces.

Buildings that are built on isolators usually have a relatively stiff cross braced beam structure that is capable of keeping the base of the building constrained to mininimal deflection from the same plane. This is NOT a foundation. The foundation is what goes into or rests on the ground. The isolators are used between the foundation and the base structure.

[ChrisG]

I can send you a picture of my model if you don't mind giving me your email address.

We usually don't post email addresses in these forums, but you can upload a photo to this forum by starting a new post, and then clicking on the "upload attachment" tab under the "save" "preview" and "submit" buttons. I believe there is a file size limit, so you may need to shrink/ compress your image if it doesn't work the first time.