Since people are still asking about how the bridge was loaded let's go through that one last time or read all of my blog Aug 02,2007 "Bridge a Bad Sign of Modern Reporting" on Dailykos. The short version is there are eight lanes on the bridge. The TWO Outside Westbound lanes(South into the city) were in use by the public; the two Inside Westbound lanes were loaded with heavy machinery, tools and workers. The TWO Inside Eastbound (North) lanes had Eastbound public traffic going out East(North). The Two Outside Eastbound (North) lanes were empty. I think the heavy off-center loading let a cracked frame member close to the East footing on the South set of footings on the West bank go into tension that it couldn't take and it failed. I think the bridge fell, starting close to the West bank of the Mississippi going out in both directions.
The lesson that should be learned from the Minneapolis bridge, see my blog Aug 04, 2007 "Minneapolis bridge Lessons to Learn" Dailykos, is that one of these old style bridges should not be in use by the public when it is being repaired.
I have no doubt that MNDOT looked at the bridge time and time again and thought the frame members could take the COMPRESSION that they saw. I also have no doubt that they never thought any of the members would be in the massive TENSION from this type of off-center load on the old frames. What failed first we may never know.
I do know new Federal Regulations should mandate all repairs on these old style bridge designs should be done with the bridge OUT of service and ALL public traffic re-routed.
Plan ahead and re-route the traffic before the job starts or we will run a high risk of paying a terrible price in lives and money. If the Feds don't make a rule change about the public safety of a bridge under repair while in use, I think we should take the example of money over safety to the local and State level and demand we have local rules about bridge repair and extremely tough rules about these types of bridges.
In my mind there is no way any engineer could look at one of these old bridges and foresee the crazy loading this bridge took while the deck was being tugged and cut on on the Two inside West lanes and traffic was moving on the two cantilever far West lanes.
If a local bridge in my area of travel is being repaired I know I'll find another route.