The investigation has started on the Big Dig tunnel collapse that killed a woman and here’s the start of a Boston Globe story titled “Workmanship and design of tunnel are called into question - Problems with bolts, glue found in other tunnel in '98”:
Investigators unraveling how concrete ceiling panels cascaded onto a car in one of the Big Dig tunnels should focus on some basic, troubling questions about the way the tunnel ceiling was built, civil engineers and highway construction specialists said yesterday.A threaded rod failed and a suspended load was shifted to other supports, which could not carry the extra weight, leading to failure. This sounds to me to be exactly the critical design flaw that lead to the structural failure of the Hyatt Regency walkway in 1981.
Officials from the Massachusetts Turnpike Authority suspect that the accident that killed Milena Del Valle began with the failure of a single steel hanger that helped hold up the concrete ceiling, setting off a chain reaction that caused other hangers to fail and send 12 tons of concrete to the highway surface as Del Valle's husband drove underneath.
From Answers.com:
The two walkways were suspended from a set of steel tie rods, with the second floor walkway hanging directly underneath the fourth floor walkway. The walkway platform is supported on 3 cross-beams suspended by steel rods with nuts. The cross-beams are box beams built-up with C-channels welded toe-to-toe. The original design by Jack D. Gillum and Associates called for three pairs of rods running from the second floor all the way to the ceiling. Investigators eventually determined that this design only supported 60 percent of the minimum load required by Kansas City building codes.The Big Dig has become a kind of slow-motion disaster where every three months another incident occurs, followed by a line of Boston officials waving their hands and insisting everything is safe.
3 comments:
As I was quickly scanning this page, my eye was caught by the diagram which I recognised from the Regency walkway failure. I was doing structural design when it happened. That was not a threaded rod failure, but a beam failure caused by the difficulty of doing what the designer wanted with threaded rod. In order to avoid running a nut up two stories of thread, they put a concentrated load into the area between where the rods passed thru the beam. The same failure would have occurred had they used unthreaded rods with welded collars installed in the same configuration.
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