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Title: Tragedy in the Twin Cities Post by ReeBop on Aug 2nd, 2007, 11:47pm Everyone has probably heard of the horrible tragedy of the Interstate 35W bridge collapse in Minneapolis. So far, engineers seem puzzled by the event. Adding to the mystery is that several lanes of traffic were shut down due to a repaving project and that the bridge passed inspection in 2006. Some things come to mind from news reports that I have heard. 1. A liquid deicing system was installed on the bridge a few years ago to aid in keeping ice off the roadway. Aren't these liquids caustic over time? I remember bridges on I-94 in Michigan with horrible rust damage from the use of road salt in the winter. Road salt also can get into the concrete and make the rebar rust away as well. I do remember being told that the liquid stuff being more effective can be even harder on metal objects. 2. There is a train track that runs underneath where the bridge first collapsed. A train was running on that track at a slow rate of speed and several coal cars were crushed in the collapse. Could any vibration from the train moving beneath could cause a harmonic effect on the older metal supports of the bridge? Those are questions that came to mind as I watched the aftermath this morning. Another tidbit of information released is that the bridge was in line for replacement in 2020. Did the inspectors miss something or did several elements combine themselves to create this tragic affair? UPDATE: It has been revealed that this bridge was cited for metal fatigue issues as far back as 2001. The bridge was rated at a "4" on a scale of 1 to 9 which from the CNN report means "advanced section loss, deterioration." Instead of costly metal repairs at that time, a yearly inspection schedule was chosen to review the fatigue was implemented. [smiley=detective.gif] |
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