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Originally Posted by throwittoblythe

It will be interesting to see what the final cause of failure was. They said on CNN they have a structural engineering team assessing the situation now, but they are mainly trying to determine if it's safe to send rescue workers back onto the bridge.

They interviewed a Civil Engineering professor from U of Minn. that had experience with this bridge and he made a very good point. The bridge did not fail in just one spot, the whole thing came down at once. To me, that points to a failure in design. There was one other bridge in Ohio that did this and it was a very poor design. One of the upper cable supports snapped and caused a chain reaction which made the entire thing come down in like 10 seconds.

Also, you have to keep in mind that this bridge was designed and built some 40 years ago. So, they designed for what they felt was necessary. How many cars drove over that bridge on average right when it opened is probably far less than what drove over in the passed few years. We use safety factors in civil design which are supposed to account for these things like increased load, partial failure, things like that. For example, we increase car loading by 60%. So, if you estimated 100 cars on the bridge at the maximum load, you would design the members to hold 160 cars. However, you can't design for everything and you can't predict the loads on a bridge some 40 years into the future.

This brings to light the fact that in the US our infrastructure is deteriorating at a much greater rate that we can build it. Cities are growing way too fast to keep roads/bridges/buildings up to standards so that they can be used safely. There simply isn't enough money or time to fix all the problems within the infrastructure at the same pace as is necessary. Look at how big of a headache I-235 has been in Des Moines; it took over 6 years to get that project completed (and it's still not completely done) and it will be over capacity in probably less than 10 years.

No matter how you spin it, this is tragic. Hopefully it wasn't some mundane error which could have easily been prevented which caused the collapsed. Whatever the reason, there will be no excuse.

I don't think they could have underestimated the weight of cars on it. Worst case, they would assume bumper to bumper trafic and then add a significant safety factor. I don't know that bumper to bumper trafic could weigh much more now than it did 40 years ago.