Name: Shake tables are way more complex than I thought
Uploaded: 2026-01-18T17:12:01.000Z
Duration: 8 min 28 s
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California gets earthquakes, which means that the building codes here have some pretty strict requirements.

There's a lot you can do with computer simulation, but

at some point, new building techniques have to be tested in the real world.

The massive 10 story building behind me has been constructed to test and certify a new design.

Basically, there's a massive heavy wood and steel spine that runs all the way up from the floor to the roof.

Bracing and dampening, the whole thing, with which, along with new fireproofing, might allow wooden buildings to be far taller than ever before.

Well, to really test it, you need an earthquake, so we're about to get one.

The building is sitting on the shake table here at the University of California, San Diego.

This whole site is locked down because that table is ready to go.

I was here a few months back while that building was still under construction, and

one of the folks in charge showed me round while everything was powered down.

We started in the equipment building where there's colossal accumulators and pumps that pressurise hydraulic fluid to 5,000 psi, which is more than 100 times the pressure of your average car tire.

If you're going along the long axis, the X direction, we can go plus minus 35 inches.

Going in the lateral, the Y axis we can go plus minus 15 inches.

And in the Z, up and down, it's plus minus 5.

We have the largest payload capacity in the world.

This 10 story building is about 700,000 pounds total.

So that's maybe 10%, 15% of our capacity.

They're going to shake a 10 story building back and forth and it's not even a big deal for them.

Also, it's not just up, down and sideways.

The shake table also does roll, pitch and yaw.

When it was Originally built about 20 years ago, it did only go back and forth in one direction.

They can shake in precise mathematical sine waves if they want to for a particular experiment.

But these days they can also replay actual records of real life earthquakes.

Although that turns out to be far more complicated than I thought.

Before we build anything on it, we need to do some tuning for the control system.

When there's nothing on the table, we do some tuning.

Then when you put the specimen on, those dynamics, the specimen dynamics actually affect the control loop.

So we need to do some further tuning and actually filter out some of those frequencies in order to successfully move the shake table.

Oh, because if the building that you've made has a resonant frequency, it interferes with the control system.

So we need to filter out those resonant frequencies.

So you're not just playing back an earthquake.

You're trying to get as close to that as possible while dealing with whatever the building wants to do as you shake it.

So the first few tests, the building hasn't been altered in any way, then the building might shift or break, or you might change.

Next up on the tour was the connector between the power building and the shake table, where, again, there is stuff that feels like over engineering until you realize just how much mass this thing has to move.

So the red is high pressure, blue is return.

These large pipes here, they're 12 inch diameter.

I feel like every curve in that pipe was something that had to be really carefully engineered.

Every time 3000 psi fluid has to change direction, you're gonna get water hammer off.

The hydraulic shock, Right, that's the term.

It will add vibrations to the table itself.

It'll cause a lot of headache, not to mention the damage that it could do if one of these connections breaks and you're getting 3,000 psi.

And that's why the whole area is locked off right now.

Everything is charged up, Warning lights are flashing.

It's very unlikely there'll be anything wrong.

But right now, inside and under those buildings is not technically a safe place for humans, just in case.

So from here, 5000 psi in the accumulators.

3000 psi running through these pipes at who knows what speed.

And they come over here and make a U turn.

Damper system here to make sure there's no vibrations here.

So this was very highly engineered to make sure everything was okay.

Don't ask me exactly why there's a U turn in the pipes.

It's to do with retrofitting new improvements around existing concrete structures.

But I do know that no sane engineer would put a U turn in that pipe unless they absolutely had to.

Now we're actually under the shake table.

The 10 story building is currently sitting on it.

Everything you see on this side is mirrored.

So there's three of them on this side, three of them on the north side.

The vertical actuators do the up and down movement and then the roll and the pitch movement.

Because you can actuate each one a different amount.

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Shake tables are way more complex than I thought

constantly

absolutely

massive

routine