Page 290 - Thomson, William Tyrrell-Theory of Vibration with Applications-Taylor _ Francis (2010)

Sec. 9.4 Vibration of Suspension Bridges 277

Figure 9.4-1. Tacoma Narrows Bridge: Torsional oscillation. (Courtesy
Special Collections Division, University o f Washington Libraries. Photo by
F. B. Farquharson [Negative No. 4].)

been observed and recorded by Professor F. B. Farquharson of the University of
Washington.^
Since the collapse of the Tacoma Narrows Bridge, much controversy as to its
cause and behavior has taken place. Intensive research by Billan and Scanlan"*" has
pointed to the aerodynamic self-excitation behavior that was able to impart a net
negative damping to the system as in flutter, to account for the destructive
behavior of the bridge.
Although this disproves the simple resonance theory as the cause of the
bridge destruction, it is of interest here to examine some of the modes of vibration
of the bridge that have been observed. The examples here represent a greatly
simplified model^ for the purpose of illustrating the use of the material in this
chapter.

^F. B. Farquharson, Aerodynamic Stability of Suspension Bridges, University of Washington
Engineering Experiment Station Bulletin, No. 116, Part 1, (1950).
^K. Y. Billah, and R. H. Scanlan, “Resonance, Tacoma Narrows Bridge Failure, and Undergrad­
uate Physics Textbooks,” Amer. J. Physics, Vol. 59, No. 2, pp. 118-124 (Feb. 1991).
^W. T. Thomson, “Vibration Periods at Tacoma Narrows,” Engineering News Record, Vol. P477,
pp. 61-62 (March 27, 1941).