SD-Lecture03-Measuring-Vibrations

SD-Lecture03-Measuring-Vibrations - Soil Dynamics Lecture...

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Unformatted text preview: Soil Dynamics Lecture 03 Measuring Vibrations Luis A. Prieto-Portar, August 2006. A rotating mass type of excitation. Some machines have intentionally designed eccentric weights that shake their frames in a forceful manner. For example, steel sheet-piling vibrating machines use this principle, along with the application of water pressure, in order to create a liquification condition in the soil and thereby easily place these sheet-piles to great depths. A simple diagram of this type is shown below. A rotating mass excitation of a foundation-soil system. ( ) ( ) ( ) ( ) 2 2 2 2 2 1 2 2 2 2 2 2 2 1 2 1 4 e n n n n n The differential equation of motion is, mz cz kz Q sin t where Q m e U The solution maybe of the form , z Z cos( t ) where , / (U / m )( / ) Z and tan D / / D / The normalized plot of Z + + = = = = + = = + ( ) 2 2 1 2 2 1 n m n m resonant resonant /(U / m ) vs / is shown on the next slide. The angular resonant frequency f is, f f D The amplitude at the damped resonant frequency Z is, U / m Z D D = = A vibratory machine is commencing to place the steel casing of a drilled shaft. Notice the two counter- rotating masses on its lower part of the vibrating machine. Vibratory hammer driving a timber pile. Note the opposite rotating shafts on the driver. A vibro-flotation machine. This device is used to liquefy granular soils and thereby densify a column of this soil. It is used for soil improvement....
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This note was uploaded on 08/29/2011 for the course CEG 5905 taught by Professor Staff during the Summer '10 term at FIU.

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SD-Lecture03-Measuring-Vibrations - Soil Dynamics Lecture...

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