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Shaking a 275-ton Building
Roland Piquepaille writes "If you want to predict how a tall building can resist to an earthquake, some researchers have better tools than others. Engineers from the San Diego Supercomputer Center (SDSC) have built a full-size 275-ton building and really shaken it to obtain earthshaking images. The building was equipped with some 600 sensors and filmed as the shake table simulated the 1994 Northridge earthquake in Los Angeles, California. It gave so much data to the engineers to analyze that they needed a supercomputer to help them. Now they hope their study will yield to better structure performance for future buildings in case of earthquakes."
http://michaelsmith.id.au
The simulated quake must've been so big it shook the images off the linked page!
To do something right, you often have to roll up your sleeves and get busy.
Are we at the point in history where we can design a building completely inside a computer and simulate the effect earthquakes of various degrees will have on the building?
Who makes that software?
How much does it cost?
How we know is more important than what we know.
Read more...
"Wednesday, Apr 11 @ 13:13 PDT The powerful earthquake struck suddenly, shaking the seven-story building so hard it bent, cracked and swayed in response. But this was no ordinary earthquake. In a groundbreaking series of tests, engineering researchers from UC San Diego's Jacobs School of Engineering jarred a full-size 275-ton building erected on a shake table, duplicating ground motions recorded during the January 17, 1994 Northridge earthquake in Los Angeles, California. To record the impact on the building, the structure was fitted with some 600 sensors and filmed as the shake table simulated the earthquake, yielding a flood of data including stress, strain, and acceleration -- so much information that engineers were having a hard time making sense of it all. That's where visualization experts from the San Diego Supercomputer Center (SDSC) at UC San Diego came in. "
Link!
Two little dashes in the url became one superdash!
They threw a truly awesome kegger and cranked the amps to 11!
Why are they using a supercomputer?
Screw that, let's wait for Earthquakes@home - and hope the name doesn't scare off some people.
The building where I used to work and write bad software every work day used to be owned by a military contractor and was built to withstand a nuclear blast. It is no longer owned by the military contractor, but is still used by non-mil gov't agencies who want communications to remain up after emergencies (floods, fires, quakes, riots, nukes, etc.) They put their servers and communications centers there. I was told that they used to do periodic "shake tests" on it by hooking up huge cranes to each edge and vigorously shaking it for a while. It seems that would be risky because it would weaken it. Even though shaking it in tests might not topple it, it may introduce undetected fractures that may result in problems on the next earthquake or whatnot. Perhaps its infrastructure is purposely built for easy inspection, being what it was originally designed for.
Table-ized A.I.
A coworker of mine is in the department, and showed me this page: http://visservices.sdsc.edu/projects/nees/article. php
It has a video of the shake as well as high def video of the simulations themselves. It's pretty damn cool, you can watch the whole building flex and sway about on top of the the shake table, and the waves propagate through the building. (Each colored dot is a GPS sensor, 10 per floor, over 7 floors).
Link to UCSD news release with pictures.
It's too bad noone can find a way to protect steel frame buildings from collapsing due to fire...
Oh. Wait.
Technically, yes. The only problem is, any simulation is only as good as the model it uses. E.g., you can also simulate scattering of alpha particles through a foil, but if you based it on the old raising pie atom model, you'd get the awfully wrong results anyway.
Hence what these guys are doing: a good old fashioned experiment, involving an actual building on a giant table that shakes, reproducing the exact movements recorded in an actual earthquake. That's how you find out if your model and simulation are actually the right ones. If the building behaves like in the assumed models, then all's well, if not, well, someone will have to come up with a better model.
It might seem that wth, we already know the laws of mechanics well enough, we don't need experiments to test them. The problem is that any model is based on some simplifications, since you just don't have the computing power to even account for all waves, reflections and interferences in a big building with hundreds of joints and thousands of metal bars, pipes, whatever other discontinuities through the walls. So physicists get to decide what are the important parts to simulate, and which should at best be lost in the decimals.
E.g., if you want to know if a horse floats, you can just as well imagine it to be a sphere or a cube. (As the wisecrack goes, "you know you're an engineering student if you approximate a horse as a sphere, because it makes the math easier.") Actually, wisecrack aside, for that you won't even imagine it to have any shape at all, since shape is irrelevant. It doesn't really matter what exact shape it is, just the mass and the volume. E.g., if you want to know how fast a rocket reaches the moon, you don't need to know the exact shape or colour of the rocket, you can just think it's a point. Etc.
That's how we solve problems nowadays. We get to decide what is really important, and what can be safely ignored in the model.
Unfortunately, if you to be really sure that you did the right choices, you have to compare it to what happens in real life. Does your simulation really behave like the real thing in that situation? Or did your approximating the horse as a sphere lead you to a wrong solution like rolling it along the race track to win?
That's, in a nutshell, what these guys did.
A polar bear is a cartesian bear after a coordinate transform.
There is a list of all the media (including several movies) on their press release site:. php
http://visservices.sdsc.edu/projects/nees/article
This includes both real and simulated building captures (and several overlayed ones).
As reported in every other story, But this was no ordinary earthquake. In a groundbreaking series of tests, engineering researchers from UC San Diego's Jacobs School of Engineering jarred a full-size 275-ton building erected on a shake table, duplicating ground motions recorded during the January 17, 1994 Northridge earthquake in Los Angeles, California. The guys at the supercomputer center played a role, but they didn't build the building or run the test. It was obviously folks from the Structural Engineering department.
I'll chalk that mistake to sloth, not pride. No doubt, some are envious of the attention the lead guys get, but the greedy bastards deserve it. In their wrath, they shake the building, lusting for its fall and gluttonous for the massive data.
Miliken Library at caltech which was an ten story building built before 1980 had a huge eccentric weighted rotor on it's roof which every year the engineering school would Activate and drive the building into resonance. All the book shelves inside were cross braced to withstand the effect. It's still there.
Some drink at the fountain of knowledge. Others just gargle.
The saddest poem