Civil Engineering/stuctures modes

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Question
Dear Sir,

     As I understand(please correct me If I am wrong) natural frequency of a structure is the frequency at which it starts vibrating, when disturbed, and the corresponding shapes of its vibration are called modes,
Now in practical in order to get the natural frequency of a structure it should be disturbed, what is the reference of this disturbing force taken as,
Now modes are the shapes/ pattern in which the structure responds to the disturbance. What is the meaning of first mode, second mode, third mode, are they,  the successive response patterns of the structure to the same single disturbing force.

Example:  when I disturbe a object(say a starched thread or a hand held scale) its first distinguishing shape of vibration(i.e First mode), then as it decay, its second most distinguishing pattern of vibration as second mode and so on.

Regards.

Answer
Dear Faisal

Please take a look at these sites and let me know wether you had been satisfied or not.\\

http://www.uvm.edu/~mmsander/music/modes-intro.pdf

http://www.physicsforums.com/showthread.php?t=276017


Please feel free to ask me further in the case of any question.

Regards
BEH

Civil Engineering

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