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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.
so could you reconstruct downtown Tokyo with a beowulf cluster of these buildings?
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.
...but what about the stroke?
I really need some sleep.
Ok. Enough stories about using three PS3's in a beowulf cluster as a supercomputer.
Who would win this election: Andrew Weiner vs Andrew Weiner's weiner.
Yawn! The Japanese have had several thousend ton skyscrapers sitting on springs hooked up permanently with sensors, dynamic counter-weights and dampers for decades now...
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The building is only 275 tons? I am no building engineer, but that seems pretty light weight for a building, doesn't it?
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 any resident of an earthquake prone area will tell you, earthquakes don't only have lateral motion, but vertical motion as well ... Northridge was not exception. It seems like this simulation, and others, only simulate lateral forces. Catastrophic failures can and do happen in structures due to vertical forces (witness the collapse of the freeway in Oakland). Why do these shake tables not simulate vertical motion as well?
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.
Posted as Anonymous coward for obvious reason
Link corrected
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For those who didn't get the references in the above post, the on-campus shake table at UCSD has neon signs what flash the vices and virtues late into the night: http://stuartcollection.ucsd.edu/StuartCollection/ nauman/49530049.jpg
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.
No, that shake table is indoors and construction would be impossible. The real behomith is the one they have on the military base. It is an outdoor shake table, which means that one is able to build anything with anything. The indoor table is limited by the size of the crane and the size of the building.
heh heh don't sweat it, it happens to the best of us ; )
...
but i don't understand why you bothered with AC for the follow-up
This reminds me of a devious stategy for destroying a building. Basically if you can determine the resonant frequency of the building, you could make a device that oscillates at that frequency. Strap the device (or devices) onto the building and eventually the building will shake itself to pieces.
After they shake it, can they fly a plane into it and see if it collapses or is even close to it?
Very much so, yes. Excellent example of why models need to be tested, in fact.
A polar bear is a cartesian bear after a coordinate transform.
The saddest poem
I remember reading about how Tesla could calculate the resonant period of a building, then set up a small mechanical oscillator on an I-beam or some such, and make the whole building shake (eventually) via positive feedback.
...put a 275-ton super computer on the shake table to cut out the middlemen.
The parent makes a post based on NO SOLID FACT and it's insightful? What temperatures are necessary to melt structural steel at all, let alone to melt the steel in those buildings to the point of causing collapse? Can jet fuel fires reach those temperatures?
WAKE UP. The official story is a "conspiracy theory" requiring you to believe the first three steel frame buildings in history to collapse to the ground as a result of fire did so on 9/11. One of those buildings was not even hit by a plane.
Yeah. Insightful. Like a fox.
What temperatures are necessary to melt structural steel at all,
Who said anything about melt?
Structural steel -- almost any metal -- loses strength as it heats up. That's why a blacksmith heats up a piece of iron or steel before working it. It just needed to get hot enough to where the loss of strength was greater than the safety margin built in to the design. That's far short of melting point.
What a maroon.
-- Alastair
finnish company (http://www.honkatalot.fi/eng/index.html) has sold many log homes/houses to japan. why? earthquakes do not destroy those at all: if the worst happens, you just use few tools, few guys/gals to help you, and in few hours your log house is fixed. (i have no time to explain how, but ask here, and later i will explain how to fix it *fast* after (almost) any kind of EQ.)
Most of the buildings structure strength was needed for the purpose of withstanding hurricane force winds. There was almost no wind load that day.
The impact and fire where also no greater than the towers were designed to survive.
Designed to survive an impact by s Boeing 707
Speed: 1010 km/h
Maximum takeoff weight: 151,315 kg
Impact aircraft: Boeing 767
Speed: 850 km/h
Maximum takeoff weight: 204,120 kg
Yes, a 767 weighs more, but as this is slashdot we should know what matters for an impact is the kinetic force.
Design: 1,010^2 x 151,315 = 154,356,431,500
Impact: 850^2 x 204,120 = 147,476,700,000
If that doesn't raise a question for you, how about considering that thermite residue was present in the debris in the crater, and that the jet fuel on the airplanes, which burns almost the same as home heating oil didn't contain enough energy for there to be molten pools of metal several weeks after the collapse. Yet they are a common occurrence in controlled demolition done with thermite.
Also consider, before the events that day, not one steel structure high-rise building has had a total collapse due to fire before or after, yet three of them happened on that day, including one not hit by an airplane.
The Millikan Library shelves were braced after the 1971 San Fernando quake toppled them and dumped the books on the floor. This was the same quake that led to Throop and Culbertson being condemned, and damaged Gates badly enough that parts remained closed until it could be strengthened during its rennovation about a decade later. Dr. Housner's shaker did make the building sway slightly, but not enough to tip over shelves, spill the drinks in the president's office, knock the Isign to the ground, or otherwise interfere with normal goings-on at the library.
DEI
Some drink at the fountain of knowledge. Others just gargle.
The towers survived the impact just fine, as they were designed to. It was the fire (coupled with what impact damage there was) they had problems with.
Sustaining "hurricane force winds" means sustaining a side load -- which the towers did just fine. The weight of the floor (and the rest of the building above) is a vertical load, which in the normal course of things is fairly constant.
thermite residue
LOL! Do you even know what thermite is? It's a mixture of aluminum and iron oxide (rust) - they combine energetically to form alumiminum oxide and iron. Gee, do you think that an aluminum aircraft colliding with a steel framed building and sitting through an intense fire might leave some "thermite residue"? I'd be astonished if it didn't.
BTW, demolition is never done with thermite, it doesn't cut fast enough. It's done by precutting (partially) structural members and then using shaped charges to quickly and simultaneously cut them all the rest of the way.
-- Alastair
Now you're resorting the flat out misinformation. The bit about thermite residue randomly forming is priceless. LOL yourself there buddy. Thanks other AC for the good info.