Thursday, August 02, 2007
Minnesota I-35W Bridge Collapse 8/1/2007
"Officials say collapse had nothing to do with terrorism..." CNN
This message accompanied the very first reports of the disaster, reports so early they were filed by 'I-Report' as CNN terms them, or eyewitness video logs. How could "officials" arrive at this conclusion so rapidly? A growing number of the on-the-scene-as-it-happened ear-witnesses described "an explosion", or "big bang" or "very deep sound" that "was felt". Also, many eye-witness reports of a "plume of dust" or "geyser-like" spout of dust were given. The height estimates of the plume by individuals either at the scene to up to 1/4 miles away on a foot bridge that parallels I-35W ranged from 100 to 200 feet in the air. A structural engineer who was on the scene stated that he would expect that "a failure of all of the load-bearing elements across the full width of the span would be required" to result in the collapse of the bridge within 4 to 5 seconds, as was reported by people on the scene.
Okay, so here is another interesting fact. As the NTSB director on the scene was outlining their efforts, he mentioned that a computer simulation program had been made available to his department that had been written as part of a doctoral dissertation by a University of Minnesota graduate student. What was the program? A computer model of the I-35W bridge, that was able to demonstrate failure modes that the bridge would exhibit, based on specific element failure or failures. He described that laser transits would be used to take the exact measurements of the post-failure scene, then reverse-engineer via the program to identify which component or component failures would yield the scene left by the real life disaster. This should be very interesting.
"We don't know what caused this but ...a bridge in the middle of America should not just fall into a river."
-- D-MN Senator Amy Klobuchar
So why then would officials want America to believe no "terrorism" was involved, before any expert analysis had been started? Any ideas?
I have some. One thing I encourage you to read if you want background on what may have happened here: University of Minnesota Department of Civil Engineering Report MN/RC - 2001-10, March 2001. You can get a copy here. While this report indicates the bridge was not in trouble at the time, it illustrates the nature of the problem domain in this type of analysis.
To see an analysis of the bridge structure look here.