Question

ENG 303 4b.

The original Tacoma Narrows Bridge was the first suspension bridge built across the Puget Sound in Washington. The bridge was strong but relatively light, narrow, and as it turns out—(too) flexible. On the morning of November 7, 1940, in a 42 mph (68 kph) wind, the 2,800-foot (853-m) main bridge span went into a series of torsional oscillations (side-to-side and up-and-down motion) in which the amplitude (size of the motion) steadily increased. This movement tore several suspension cables and broke the main span, causing the bridge to collapse. The failure of the bridge was a shock to the engineering community. How could a structure weighing more than tens of thousands of tons topple in moderate wind? What factor(s) did the engineers of the Bridge fail to include in their engineering analysis?

Answer 1

RESONANCE :

The engineers failed include the resonane as factor in this case. Resonance is the phenomena in which the excitation frequency matched with natural frequency of the material or structure. If this happens the amplitude of oscillation will be at maximum which will result in collapse.Resonance is a phenomena that should be considered if anyone build something that oscillates or vibrates. Every structure or material will have its own natural frequency that should be identified. for eg glass will brake if sound wave that matches will its natural frequency passes through it.