This belongs under Civil/Structural, but is a Mechanical Engineering issue as well. Potential Flaw Seen in Design of Fallen Bridge, NYTimes, Aug 9 http://www.nytimes.com/2007/08/09/us/09bridge.html The use of Gussets is standard in steel bridges. They form the joints shared by various members. The objective is to design them so that stress is well below a critical failure stress, but the entire bridge system also needs to be designed to distribute the load so as to prevent stress concentrations that would lead to failure. That apparently may not be the case. It would seem necessary at this time to re-evaluate all such bridges (truss) in order to identify those which might be in danger of failing. We now have software and hardware not available in the 1960's or 70's, which can do a very good job of identifying potential problems.