## PSN-L Email List Message

Subject: Re: Shake table
From: John Lahr johnjan@........
Date: Sat, 05 Apr 2008 03:01:17 -0700

```Hi Kay,

This sounds like a great project.  I would really like to post some
pictures to my web site, along with construction details, when you're done.

I've always used variable frequency, rather than amplitude.  It's
easier to do and let's the resonant period of the model be
determined.  The best frequency (the one that causes damage!) will
depend on the height and construction of each model.  It's best if
there is a weight requirement, in that each model must carry a
considerable weight on the roof.  This could be considered an air
conditioner unit for the building or some other machinery.

One thing to avoid is providing too much time/material so that the
buildings are indestructible!   A teacher sent me a video of his
class testing their models and they were so strong that not much
happened on the shake table.  One actually fell on the floor and was
not damaged!

Cheers,
John

At 09:57 AM 4/4/2008, you wrote:
>Folks,
>
>Thanks for the feedback on the leveling screws for my seismometer.
>
>Now here is a question regarding a shake table.
>
>I currently have a small shake table that has a 10" base plate which
>I use in the public schools to help kids understand the relationship
>of building structure and materials to earthquake damage.  I divide
>the kids up into teams to construct their "buildings" and then
>individually set them on the shake table.  Because only one building
>can be tested at a time it is more time consuming and less "fun" for
>the kids because they can't easily see how their building measures
>up to another team's building.
>
>So, I am constructing a larger shake table with a 30" base that can
>hold four buildings.  This lets a class divide up into four teams
>and then the entire class can watch their buildings shake at once.
>
>Say an actual building has a footprint of 100 feet square.  Relative
>to a model building which has a footprint of 12 inches square, the
>width is a factor of 100.  I have a variable frequency motor to
>which I am attaching off center cams to create the vibration
>movement.  Springs pull back the base towards the drive shaft with the cams.
>
>So, here is my question.  Has anybody experimented with a shake
>table of this size?  What displacements should I design the cams to
>create?  I could use different size cams to create different
>"magnitude" earthquakes.  Also, what frequencies should I set the motor to run.
>
>Thanks for any help that you might offer.
>
>Kay
>

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