The Collapse of
You've probably seen the movies. The bridge begins to wobble from side to side.
The oscillations get larger and larger. Leonard Coatsworth leaves his car with his
dog Tubby inside and crawls on his hand and knees off the bridge to safety. Sud-
denly, the bridge collapses. The date is November 7, 1940, only four months after
its grand opening. The collapse came as no surprise because the Tacoma Narrows
Bridge,* or "Galloping Gertie," as it was fondly called by local residents, was
notorious--even before it opened for traffic--for a swaying and vertical undulat-
ing motion of its roadway caused by the peculiar wind currents that pass through
the narrows. See Figure 1.
After working through the problems in Chapter 5, you might suspect that reso-
nance was the culprit. Somehow the forcing of the wind and the natural frequency
of the suspension cables coincide, and thus the amplitude of the forced system (in
this case the bridge) grew without bound, eventually causing the bridge to fall. But
recent work by Lazer and McKenna suggests that the phenomenon that caused the
bridge to fail was more complex than resonance.
Most of the models presented in
their work are beyond the scope of this project. The Still Curious? section at the