Science Buddies: "Ask an Expert"

I am doing a project on earthquake damage resistance. I have 3 possible solutions that I will be focusing on. 1 is rubber dampers in the foundation of the building. The second method is a rather impratcial one but it might work. The whole building is suspended from a HUGE hanger. The third method is one that I adapted from a method to keep TALL buildings from falling down in high winds. It comprises of placing large water tanks in the top, middle, and bottom of the building, the water sloshing back and forth would counteract the shaking. I just need 1 thing, a earthquake macheine that I can control the shaking.

If you put "shake tables" into a search engine, you should get some articles including ways to make some simple ones.

If you are near a mechanical and civil engineering school with a large shake table, you might be able to piggy back on one of their test setups if your foot print is small. Often several things are placed on the table for a run as long as they are compatible.

A "sky hook" introduces another structure to hold the hanger which is suseptible to wave action. This effectively makes a large pendulum whose stability is a function of shake frequence.

Large baffless tanks (like milk trucks) are probably not a great design. There will be some shake frequency that will cause the wave action in the tank to amplify the shaking. Try stopping a partially full milk truck quickly, the a wave of milk rushes to the front bounces off the front and travels to the back which helps to stop the truck and then rushes forward and hits the front pushing the truck several feet further that where it looked like it was gong to stop.

The key to using any dynamic damping is having a control system that will change the tuning so as to dampen and not add to the oscillations over the entire expected wave frequency range.

could you give any suggestions on methods that I can use? Most shake tables that I see on a search engine are not controlable.

could you give any suggestions on methods that I can use? Most shake tables that I see on a search engine are not controlable.

Welcome to the world of problems that engineers have to struggle with in terms of creating test equipment to assist with scientific and/or engineering investigations. The first people working in an area often spend 90% of their time and effort on coming up with test and measurement equipment and they often have to find simplifications and reduce their scope in order to make any progress.

What grade are you in and what math classes are you currently taking? Have you had physics?

I am in seventh grade, in ap math and have a OK grasp of physics.

i found a good website try this one out:
http://jclahr.com/science/earth_science/shake/

I am in seventh grade, in ap math and have a OK grasp of physics.

Unfortunately, 7th grade ap math experience can vary significantly from school to school.

Have you been exposed to any kind of functions? Do you know what a vector is? I'm trying to get a more accurate starting point how to explain waves and forcing functions and responses.

Some simple demonstrations of waves deal with dropping a marble into a large bowl or pan of water. The wave front propigates out in a circle. Its amplitude is the height differential from the top of the wave to the trough and it diminishes with distance traveled. If you have a cork floating in the water, it will be pushed by the wave front and also tilted by the wave front. In other words there is a complex horizontal and vertical effect on the cork in the water. The cork will also cause a portion of the wave front to be reflected. When the wave front reaches the sides of the container, it will reflect back as well.

Do some research/reading on waves, wave propigation, damping, reflection, amplitude, and mathmatical functions.

Commercial shake tables are designed to cause horisontial displacement, vertical displacement, and complex horizontal and vertical displacement at various amplitudes and frequencies with various repetition and decay.

If you simplify your study to only investigate horizontal displacements which is the largest component seen seen at long distances from the fault, you should be able to build something using a variable speed electric drill with an eccentric and follower with a variable lever multiplier to move a platform (piece of plywood) sitting on top of dowel rods.

To investigate the waves coming from different directions, you simply rotate what you place on the platform.

The drill speed will control the frequency and the lever fulcrum will adjust the amplitude and how fast you squeeze and release the drill trigger will affect the attack and decay of the waves. The attack and decay won't be very repeatable so analyzing what happens in steady state for longer periods is probably what you are going to be limited to with homemade equipment.

I've used a lot of technical terms that are probably new to you so look them up and post back any specific questions.

I might have found my methods to test! The first one is simple, pure reinforcement. Hopefully it will stifen the building enough to keep it from falling apart, while leaving it flexible enough to still shake. #2 is lead-rubber bearings (I will use graphite) which are already in use. The third method is a combination of the two. PLEASE!!! give feedback!!!

I'm not sure I am visualizing the bearings, but in concept what you are trying to do seems reasonable. Keeping in mind that it is 20 years since I studied any civil engineering with respect to earthquake bracing.

Assuming you've managed to set up a shake table and construct a "building", you'd want to try it out:

1. unreinforced

2. with "earthquake bracing" - there are a variety of ways to do this, the most typical is just boards that attach the building mechanically to the foundation. I think though what you're describing is reinforcing the building frame itself, making it out of stronger/stiffer materials or adding some kind of extra material to make the walls stronger. You may want to look up "truss" when doing this, generally extra material added in triangular formations gets you the most effect for the minimum added bracing material/weight.

3. with some kind of foundation that the building "floats" on, which damps the effect of the earthquake by decoupling the building motion from the earth motion. I believe that's what you are getting at with the lead/rubber bearings.

4. with both earthquake bracing and modified foundation

I think what you are doing is very interesting but also very challenging. Good luck with it and please do report your progress and results here so we can all see it.

Thanks Everyone for giving feedback and help! Yes the lead-rubber bearings are a way of isolating the foundation, and I meant to reinforce both the structure and the foundation.

here is the link for the lead-rubber bearings: http://leadrubberpretread.blogspot.com/ I hope this will help.