Reply #21: thanks - but I should repeat my disclaimer

[frogcycle]

I am mostly guessing from sketchy incomplete data.

I have heard that there were comments in the more-recent reports about a lack of redundancy in the design. If that is true, then the problem goes back to 1967, and somebody is a flaming idiot.

A fundamental in designing something like this is to look at failure modes. You design it not to fail, but then ask "what if?" You have secondary and tertiary plans - whether its a structural design, or a system design. For those components that are "single point of failure" you have a strategy to shut down, or abort the mission, whatever, withouf catastrophic failure.

Katrina would be an example of NOT doing that. You build levees, install pumps, etc, and theoretically have a fail-safe design, then you say "but what if the storm is THIS big and the levees are breached?" that's why submarines have watertight compartments, and why NOLA should too (see my plan on that topic: http://www.dbc3.com/NOLAPlan). But I digress.

At some point you have to make a trade-off. NASA says "ok, we have done everything we can, tried to anticipate every eventuality, have backup systems, backup plans, and backups for the backups. We still expect to lose a shuttle every x number of launches."

For space flight you have to do that. For NOLA, lacking a complete rethinking and redesign (again, see my website), you also have to do that. For the Space Station they have escape modules. For the shuttle, they know they'll lose the crew. For something like this bridge, you really don't have to do that. A proper inspection and honest appraisal of its condition, should, in my opinion, have found it to be on the verge of disaster. Or the inputs were so unexpected, so out of spec, that it is a freak incident. In which case it should have had sufficient redundancy that if, say, one major support beam broke loose from the ground support at one end, then that portion of roadway would have failed, there would have been a minor disaster, but the span would have stayed up = like an airliner flying on one engine with two out of commission. It would have had to be condemned, to be sure, but the whole damned thing would not have dropped like a rock. Either grossly risky design, or gross lack of inspection, or gross bad judgement on the data.

I expect all three, with the latter being driven by some twenty-something Liberty University grad.