Engineers can't wait around for the next big one to hit. So, they use a huge platform to simulate an earthquake.
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Transcript:
- [Voiceover] On an October afternoon in 1989, a major 6.9 magnitude earthquake, brought Northern California to a standstill. The Loma Prieta Earthquake was the strongest to hit the region in over 80 years. It killed 63 people and injured nearly 4,000 when sections of bridges failed, buildings collapsed, and freeways buckled. Property damage was estimated at $6 billion. And geologists tell us future quakes are coming, it's not if, but when. What can we do to make our buildings and bridges safer before the next big earthquake hits?
- The simulation of earthquakes is a big part of what we do.
- [Voiceover] Khalid Mosalam is the Director of the Pacific Earthquake Engineering Research Center, headquartered at UC Berkeley with testing facilities in Richmond, California. To test how different structures respond to the complex forces of an earthquake, the center's research engineers rely heavily on a piece of equipment called a shaking table. Engineers use this shaking table to simulate real earthquake conditions on just about any structure that they want to model.
- The shaking table is one of the hallmark pieces of testing equipment that we have. It's 20 feet by 20 feet, it's made of reinforced concrete so that the table can be very stiff.
- [Voiceover] Beneath the table are mechanical devices called actuators, that working together, can simulate an earthquake. Two actuators shake the table along the X axis, two shake the table along the Y axis, and four shake the table vertically, along the Z axis. Additionally, the table can also rotate independently along each of these three axes.
- So we have a very large database of these recorded motions from past earthquakes and we have a computer that is connected to the table that drive the table, and in this computer we put the exact signal that was recorded in that particular earthquake in a digitized form.
- Okay the table is clear.
- [Voiceover] Clement Barthes oversees most of the tests performed on the shaking table. Companies often come to him to test how their equipment will perform during an earthquake. Today, a company is anxiously waiting to see how their new concrete wine tanks stand up to an earthquake. Two different scenarios are being tested. On the left, the wine tanks are free standing on the shaking table, on the right, the tanks have been bolted down. In the control room, Clement dials in a simulation of the 2014 Napa Earthquake. at first glance, it may appear that bolting down the tanks is the way to go, but upon closer inspection, Clement finds a crack at the base of the wine tank. The best method to secure the wine tanks will need further research.
- [Clement] We observed very satisfying behavior when we simply let the horse tack rock, and it leads to that idea that maybe it wasn't a good idea in the first place to bolt these units down and maybe they are behaving better if we simply let them rock.
- [Voiceover] Letting a structure rock has actually come to be one of the most effective methods of protection from earthquakes. In fact, one of the most significant developments to come out of testing on the shaking table is the proof of concept for energy dissipation devices.
- [Grace] Basically it's something that takes the accelerations or the energy from one source, and basically dissipates it so that the impact of the earthquake to the building structure itself is minimized.
- [Voiceover] The building may sway and even develop small cracks, but major damage is avoided.
- This technology is used very commonly now, 30 years after the original testing was done in the early 1980's.
- [Voiceover] In 1999, San Francisco City Hall was retrofitted with these devices. A year later, the International Terminal at San Francisco Airport was one of the largest structures in the world to be built on base isolators, a kind of energy dissipation device. Still, in earthquake prone areas like California, there are thousands of structures that wont' be able to withstand the next big earthquake. But with the help of the shaking table, engineers have more tools than ever before to protect against earthquakes, both large and small.
