January 16, 2007 - NTSB Safety Recommendation
Yesterday the National Transporation Safety Board released a safety recommendation that addressed a design issue related to the August 1, 2007 I-35W bridge collapse.
The Safety Board is concerned that, for at least this bridge, there was a breakdown in the design review procedures that allowed a serious design error to be incorporated into the construction of the I-35W bridge. The bridge was designed with gusset plates that were undersized, and the design firm did not detect the design error when the plans were created. Because of this design error, the riveted gusset plates became the weakest member of this fracture-critical bridge, whereas normally gusset plates are expected to be stronger than the beams they connect. Further, there are few, if any, recalculations after the design stage that would detect design errors in gusset plates. Finally, other programs to ensure the safety of our Nation's bridges, such as the methods used in calculating load ratings and the inspections conducted through the NBIS program, are not designed or expected to uncover original mistakes in gusset plate designs or calculations. (from the Safety Recommendation Letter)
Additional resouces are available on the Government Publications Library I-35W Bridge Collapse site.
The final report regarding the bridge collapse is projected to be done by year end.