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Shvoong Home>Science>Engineering>Tacoma Narrows Bridge(Fluid Mechanics) Summary

# Tacoma Narrows Bridge(Fluid Mechanics)

Article Summary   by:EngrYasirNawaz     Original Author: Yasir Nawaz

You have heard of the collapse of the Tacoma Narrows Bridge but some of you donot know
the reason behide it,for general people i would say that it is due to resonance and for fluid mechacnics i will say that it is due to avoidance of the principal of fluid mechanics .Now that i told the reason i must explain it to general people because the mechanical engineer knows how it collapse but i will not ignore them completely because they are more interested in it so i will explain to them what to care about when building a Bridge .
Resonce occur when a system is excited by the continued application of external force at the natural frequency (Every body have certain frequency including humans but the frequency of human body is very very very small so in practical life we dont experiance it.)so with the application of external forces at the natural frequency ,which is the frequency at which the system would vibrate if deflected once and then alllowed to move freely ,the amplitudes of the oscillation(you can think oscillation as the up and down motion of something through neutral postion) willl build up and it will destroy the structure due to high amplitude(high up and down) oscillation.
The collapse of the Tacoma Narrows suspension bridge at Puget Sound, Washington, in 1940, for example, was caused by wind-excited vibrations at the natural frequency of the structure due to which the bridge started high up and own motion and the structure was not able to hold this high up and down motion and hence collapsed.
On the other hand, vibrations that are not at the natural frequency(the integer multiples of the natural frequency), tend to die out rapidly. A violin string, for example, is excited over a wide range of frequencies by the drawn bow. Only the basic frequency of the actual note heard , which have a smaller amplitude, however, will persist at an audible level. For mechanical engineers i will say that Resonance of a structure is usually avoided by changing its stiffness or its mass. Increasing the stiffness increases the natural frequency, and increasing the mass decreases the frequency
Resonance can also occur in mechanical, structural, and acoustical systems.
Published: March 01, 2008
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