Tacoma Bridge

Theory and Knowledge

Gadabout viewed this video while attending Michigan State University during an undergraduate course in Vibration Theory (Gadabout is a scientist). As you can see from the video, structures made by man are susceptible to failure. In this case, vibrational effects from natural winds set the stage for the natural harmonic of the bridge to become unstable, traverse the entire length of the center span resulting in failure. I remember being fascinated by this film clip as a young college student.

It has been a very long time since I have studied engineering, so I’ll pass on trying to go much farther into detail and embarrass myself, but I would like to take this opportunity to point out that much of what we create is based on Theory. There is a big difference between theory and knowledge. Theory, data and knowledge are framed in many different references, colors and varying shades of understanding.

Engineers, scientists, doctors and various other creators design, build and observe their outputs. The output in Tacoma was a bridge. The outcome of the design was failure in the form of an unforeseen harmonic vibration. This sent the engineers back to the books and their calculations to eliminate future design flaws. Many years ago, doctors used the practice of bleeding patients to cure illnesses. The benefits of bleeding were based upon a theory; and a silly theory by today’s standards.

Theories cannot be proven wrong, because they are not facts. Take the leap of faith, folks. Theories are simply replaced by other theories. Remember, gravity is a just a theory!

Global Warming is a theory. Fact (knowledge) is that the planet has shown a warming trend during the past century. Theories as to why the planet is warming vary.

Evolution is a theory. The existence of God is a theory. The “Big Bang” is a theory.

What happened to the bridge in Minneapolis will be determined using vibration theory, modeling and simulation, and a host of other investigative techniques. I find it rather alarming that the story in Minnesota is framed in a political and broad descriptive data viewpoint. Political, since it has been linked to the President’s “failures” with Katrina. Descriptive data, since we all are told that 70,000 other bridges across the nation are in the “same condition” as the collapsed bridge. We are told to be scared.

My theory is that the said bridge collapsed due to a combination of initial design flaws, age, minor structural failures, winds, temperature, loading patterns and the “fact” that repairs were underway. Most likely a sudden vibrational event occurred when many factors came together at a single point in time. Tragic, but we should be thankful that more did not die that day. I am surprised that the Press has not shown the film clip of the Tacoma Narrows Bridge. It’s my theory that Tacoma is a forgotten event. Gadabout Jack hasn't forgotten, especially since he has driven over the replacement bridge many times.