Bridge Collapse Center of Attention

Although Britney Spears and Lindsay Lohan both came close when they had their recent brush with the law, we haven't seen any single news event take over the picture box of Yahoo News' popular page since Knut the Polar Bear.

Unlike the celebration of "cuteness" that is Knut, this attention is derived from calamity.

The I-35W Mississippi River bridge shares the same mile of the Mississippi as two of Minneapolis' other spectacular catastrophes: the explosion of the Washburn "A" Mill in 1878 and the collapse of the tunnel under Hennepin Island in 1869, which nearly destroyed St. Anthony Falls.

The I-35W bridge was notable for not having any piers in the water. Instead, the main support piers were located on the banks of the river, and were built of tubular-shaped concrete pillars. The main bridge deck was supported by a single 458 foot long steel arch over a 390 foot wide navigation channel. Two sets of locks and dams just upriver of the bridge were constructed a few years earlier to allow passage past Saint Anthony Falls. The bridge was one of the widest bridges in the Twin Cities area and provided an important link for Interstate 35W traffic.

On Wednesday, August 1, 2007, the bridge failed catastrophically at 6:05 p.m. CDT (2305 GMT) during the evening rush hour, causing 50 or more vehicles, their occupants, and several construction workers to fall into the river or to its banks. Several vehicles caught fire among the debris, including a semi-truck, forcing fire crews to route hoses from several blocks away in an attempt to put out the flames. In addition, a portion of the bridge fell onto a freight train parked beneath the structure. No one was on the train and the line carries no passenger trains.

Road construction on the bridge had been ongoing for several weeks prior to the collapse. Shortly before the incident, the Minnesota Department of Transportation announced that it would reduce the bridge to one lane in each direction during the late evenings of July 31 and August 1.

Over 60 people were reported injured in the collapse, many of them severely, and initial reports indicated at least nine deaths, although that number has officially been reduced to four confirmed. Drivers were stranded on parts of the collapsed bridge that were not submerged. 60 children, aged four to 14, were riding a school bus that was on the bridge at the time of the collapse, returning from a field trip. The bus made it most of the way across the bridge before the roadway collapsed underneath the vehicle. Reports indicate that all passengers on the bus escaped safely.

At this time, the cause of the collapse remains unknown. A 2001 Mn/DOT report indicated weakness at the joints of the steel that held the concrete deck above the river, due to "unanticipated out of plane distortion" of the steel girders. The report also noted a concern about lack of redundancy in the main truss system. Being a non-redundant structure, the bridge had a greater risk of collapse in the event of any single structural failure. In 2005, the bridge had been characterized as "structurally deficient" and in possible need of replacement. This was reportedly reflected by its rating in the US Department of Transportation's National Bridge Inventory database.

BTW -- If you have yet to use Wikipedia for breaking news coverage, you are denying yourself an amazingly helpful resource in making heads or tales of conflicting news reports.