http://www.nytimes.com/2008/01/15/washington/15bridge.html?_r=1&ref=us&oref=slogin
Investigators said Monday that the Interstate 35W bridge in Minneapolis, which collapsed into the Mississippi River on Aug. 1, killing 13, came down because of a flaw in its design.

The designers had specified a metal plate that was too thin to serve as a junction of several girders, investigators say.

The bridge was designed in the 1960s and lasted 40 years. But like most other bridges, it gradually gained weight during that period, as workers installed concrete structures to separate eastbound and westbound lanes and made other changes, adding strain to the weak spot. At the time of the collapse, crews had brought tons of equipment and material onto the deck for a repair job.

The National Transportation Safety Board has scheduled a news conference for Tuesday to discuss its investigation.