Shaking a 275-ton building
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.
Below is an image of the seven-story building that was used to record the pseudo-earthquake (Credit: SDSC).
With all this data that was recorded during the earthquake simulations, SDSC visualization experts have created movies showing how a sensor-equipped building gave them a powerful tool to explore structure performance from different perspectives in full-scale earthquake shake table experiments. (Credit: Amit Chourasia, SDSC Visualization Services). And here is a link to a larger version of this picture.
This project has been conducted at the SDSC's Englekirk Structural Engineering Center. The interdisciplinary team used the world's first outdoor Large High Performance (LHP) shake table developed for the Network for Earthquake Engineering Simulation (NEES) project. This UCSD LHP Outdoor Shake Table is located at the Field Station at Camp Elliott, a site located 15km away from the main UCSD campus.
"By recreating the shake table experiment in movies in a virtual environment based on the observed data, this lets engineers explore all the way from viewing the 'big picture' of the entire building from a 360-degree viewpoint to zooming in close to see what happened to a specific support," said SDSC visualization scientist Amit Chourasia. "Integrating these disparate data elements into a visual model can lead to critical new insights."
But don't believe it was easy to produce these movies...
"When we tried to composite the actual video footage, we found that the instruments had sampled the data at 50 Hz but the video was recorded at 29.97 Hz.," Chourasia explained. "And there wasn't any timing synchronization between the building sensors and camera." This posed a serious hurdle for compositing. "After viewing the video footage, we noticed that the recording also contained audio data, because the moving building and shake table make noise, and this proved to be the key." By "listening to the building" and analyzing the audio and sensor signals, the researchers were able to synchronize the video and instrument data for the visualization.
For more information, this research project has been described in ACM Crossroads, , the student journal of the Association for Computing Machinery, in a special issue focused on computer graphics (Issue 13.3, Spring 2007). Here is a link to this article, "Digital Re-creation of a Seven-Story Building Shake during an Earthquake." You'll find more images and animations related to this project on this page provided by the Visualization Services of SDSC, including the top image of this post. But be warned: some of the videos are quite large -- from 2 to 50 MB).
Sources: University of California at San Diego news release, via EurekAlert!, April 11, 2007; and various websites
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