Huntsville University Drive Bridge Vibration

This bridge, near the University of Alabama in Huntsville, was built so that pedestrians and cyclists could safety cross over the road. The support structures on either end have both stairs and gentle ramps.

The bridge’s fundamental frequency is 2.2 Hz with 0.16% damping. The damping is very low. These values were determined via experiment in  Bridge vibration report.

The triaxial accelerometer & data logger was a Slam Stick provided by Mide.

The Matlab scripts for the accelerometer data post-processing are included in the GUI package at: Vibrationdata Matlab Signal Analysis Package

See also: London Millennium Bridge Vibration

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Here is another Huntsville-themed paper: Huntsville Hospital Tram Vibration

– Tom Irvine

Tacoma Narrows Bridge

Tacoma Narrows Bridge Torsional Oscillation

The original Tacoma Narrows Bridge was opened to traffic on July 1, 1940. It was located in Washington State, near Puget Sound.

Strong winds caused the bridge to collapse on November 7, 1940. Initially, 35 mile per hour winds excited the bridge’s transverse vibration mode, with an amplitude of 1.5 feet. This motion lasted 3 hours.

The wind then increased to 42 miles per hour. In addition, a support cable at mid-span snapped, resulting in an unbalanced loading condition. The bridge response thus changed to a 0.2 Hz torsional vibration mode, with an amplitude up to 28 feet. The bridge collapsed as a result.

Here is a paper that gives an explanation of the failure in terms of aerodynamic self-excitation: Tacoma Narrows Bridge Failure

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Here is a brief video clip that shows both the bending and torsional motion: video

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See also:

Volgograd Bridge Oscillation

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– Tom Irvine