The Big Dig |
Engineers have taken us out of the caves and up to the skies, linked us with far away shores, and connected us to distant lands. And along the way they’ve also made some pretty huge mistakes. Stephen G. Banzaert, an instructor at MIT’s Edgerton Center, teaches a course called “Spectacular Failures in Engineering and Other Experiments.” ThePhoenix.com checked in with Banzaert to see if the recent Big Dig disaster qualifies as a spectacular failure, and to find out his speculations on what, exactly, went wrong. What follows is an edited transcript of the e-mail conversation.Would you consider including the Big Dig on your syllabus this fall?
Given how long I've now spent on the phone talking about the Big Dig, I think it's almost a certainty that it will be on the syllabus this Fall, although it may yet be too soon to draw any real conclusions from it.
What are the "Spectacular Failures" that you teach in your class?
We range from the Boston molasses flood, to an explosion of a gun on the USS Princeton, to both shuttle disasters, the THERAC-25, and the Bhopal chemical disaster. We focus primarily on disasters that present lessons to engineers and organizations on how to do better in the future.
What took you to teach your students the bad example?
My class is geared towards freshmen as an introductory course in the history and causes of engineering failures. Last year I had 20 students. It's a new version of a class I took as a freshman at MIT (class of '98), which had left the catalog a few years before I returned as an instructor. I started teaching it because I think engineers in general benefit from learning this history, and perhaps more importantly from learning how to recognize the environments that allowed some of the "classic" failures to happen. As I mention in the description of my class, it's a humbling proposition to think that most failures are caused by motivated, qualified, highly trained people who are doing their best and think they are succeeding. It's hard to see your own blind spots — hence, for example, the need for external review.
Can you shed some light on what went wrong with the Big Dig tunnel’s ceiling?
I have no idea what went wrong. Anyone who has direct engineering knowledge of those ceilings is, for now, not talking. Until we really understand the mechanism, there's no telling what happened.
The first bit of information that came from Big Dig authorities was that a hanger bolt failed and that caused the ceiling to fall. The question of the (early) hour was: Did the failure of one hanger bolt actually cause this collapse, or was there a larger network of failures (such as many weakened hangers, with one actually failing and precipitating the collapse)?
Typically, designs of this nature come with substantial redundancy such that the failure of a single member can't cause a collapse like what we saw. (For example, your car doesn't lose a wheel if a single nut comes unscrewed. You would either need several nuts coming off, or all of the nuts to be weaker than specified, in order to be able to rip a wheel off.) There's no telling what the actual scenario here is until some skilled structural engineers spend time poring over the blueprints.
