Shake Table

This small shaking table allows us to demonstrate how different buildings react to different frequencies of earthquakes. It also allows us to demonstrate how we can make buildings safer in the event of an earthquake. Unfortunately, we cannot show the motion of the buildings on the website (see The End! if you want to arrange a real tour of the lab), but have been able to take snapshots of the buildings' motion and show what we can do to make buildings safer.

One of the ways we can help make buildings safer is to make them react the same way as one another during an earthquake. One of the dangers is that buildings of two different sizes respond differently to the frequencies of the earthquake. This means that when the shaking gets bad enough to cause damage, buildings will actually start hitting each other and destroying themselves. One could see evidence of this from the Nisqually earthquake. The older buildings in Pioneer Square in Seattle, as well as the older buildings in downtown Olympia had this problem. (Picture by FEMA)

 

If the buildings shake simultaneously, then this reduces the damaged caused by the earthquake. How can this be done? If we follow the picture sequence below, we can see how this works. In the first picture, we can see how the buildings are colliding into each other when the shake table is turned on. In the second picture, we add weight to the smaller building so it behaves like the big building. This added weight is making up for the two extra floors that the big building has. If we now turn the shake table back on, we can see in the third frame that they behave the same. While it is difficult to capture the motion in a photograph, we can see that they no longer collide (the shaking is turned on to full power in the last photo).

 

The other way to reduce damage is to add giant rollers to the bottom of the buildings. By placing rollers under the foundation, we can see that there is virtually no shaking of the buildings. The problem with this method is that it is very expensive, and is even more expensive and very difficult to do to buildings that have already been built. This method has been used on a few landmark buildings here in Seattle. Can you guess which ones? If you said the Safeco field stadium and the new Seahawks stadium, then you're right. Underneath their foundation lie giant rollers that keep the stadium from shaking to a great degree from an earthquake. If we look at the pictures below, this is once again demonstrated by the shake table. Even though it is difficult to tell in the picture on the right, one can see that the buildings are barely moving.

 

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