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."

Shakey

[Tablizer]

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.

Picture LInk

[Pinky3]

Link [ucsd.edu] to UCSD news release with pictures.

Re:Any structural engineers around?

[Arclight17]

I imagine that the software is custom written.
But it wouldn't surprise me if there were a market for such a thing... Include some other foreseeable disasters (fire, flood, airplane, Michael Jackson...), and sell it to major construction companies in skyscraper or other 'secure' building markets.

And just for kicks, maybe add an easter egg like sim city, so that you can destroy your buildings with aliens, dragons, etc. :-D

Is it Accurate?

[Anonymous Coward]

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?

Re:The only problem is

[AJWM]

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

True enough for moon rockets, but for some simulations -- like projecting whether a given asteroid (1950 DA [nasa.gov] for example), the colour does matter if you're project the orbit to see if it hits Earth in 800 or so years. Over such long time intervals the difference in sunlight pressure (and a couple of related effects) on a light vs dark surface will affect the trajectory.

The same effects have an affect on the rocket too, of course, but as you point out, on that scale they're not important.

Re:Shakey

[Anonymous Coward]

What you describe is a good application for eccentric mass vibrators, if you can affix one to the structure. I do appreciate the scale of the shake table these folks built, but sometimes you can't move the structure to your shake table to test it.

Eccentric mass vibrators are just like the cell phone vibrator (or other things you know of that vibrate) but much larger. And you strap these to the roofs of large buildings, wherever they are.

This is a crude Wikipedia article on it: http://en.wikipedia.org/wiki/Vibrator_(mechanical) [wikipedia.org]

Here's a good example of one at UCLA: http://nees.ucla.edu/eccentric_mass.htm [ucla.edu].

Another interesting way to do structural testing is called snapback testing. A lot like when you played tug-of-war with your friend, but you let go of the rope. So you attach cabling to a structure and force it to be bent by pulling really hard on it. The coupling mechanism allows for rapid de-coupling of the force being applied (i.e., it lets go). The structure snaps back to its original position, and in so doing you can analyze its dynamic behavior under roughly controlled conditions.

Shaking Building Not New

[goombah99]

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.