Why the Tacoma Narrows Bridge Collapsed

Following the collapse, the Washington state government 

- Tacoma Narrows Bridge. Failure of the Bridge. A Reprint of Original Reports.

The Tacoma Narrows Suspension Bridge collapsed on November 7, 1940. Immediately after this catastrophe several Boards of Engineers were appointed by the different agencies connected with the financing and construction of the bridge to report on the causes of failure, amount of damage, and cost of dismantling and rebuilding. These Boards made their reports to the agencies by which they were retained. The Advisory Board on the Investigation of Suspension Bridges obtained additional copies of these reports and arranged to supply technical libraries with assembled and corrected copies.


- The FWA ("Carmody") Investigation Board.

The State of Washington and the United States government both appointed boards of experts to investigate the collapse of the Narrows Bridge. The insurance companies established a "Narrows Bridge Loss Committee."

The Federal Works Administration appointed a 3-member panel of top-ranking engineers: Othmar Amman, Dr. Theodore Von Karmen, and Glen B. Woodruff. Their report to the Administrator of the FWA, John Carmody, became known as the "Carmody Board" report.

In March 1941 the Carmody Board announced its findings. Three key points stood out: (1) The principal cause of the Narrows Bridge's failure was its "flexibility;" (2) the solid plate girder and deck acted like an airfoil, creating "drag" and "lift;" and (3) aerodynamic forces were little understood and engineers needed to test all suspension bridge designs thoroughly using models in a wind tunnel.

The Board refused to blame any one person. The entire engineering profession was responsible, said the experts.


- Twin Views of the Tacoma Narrows Bridge Collapse.

After the various studies of the collapse, a new suspension bridge was constructed at the same location . The new bridge is four lanes wide and has open grid sides instead of solid I-beams . It was opened on October 14, 1950, and has not displayed any of the interesting oscillatory properties of the first bridge