Dissertation/Thesis Abstract

Experimental verification of flexural guided waves in concrete cylindrical piles
by Lynch, James J., Jr., Ph.D., Northwestern University, 2007, 473; 3284190
Abstract (Summary)

Two experimental methods have been developed to induce flexural waves in concrete piles for which a portion of the shaft is accessible, and the test results were compared to theoretical solutions of flexural guided wave propagation. The pile response is measured and the results are analyzed to compute the group velocity - frequency relationship or the phase velocity - frequency relationship. The experimentally-determined velocity - frequency values are compared to theoretical values of velocity for the flexural branches. Three prototype piles were evaluated nondestructively by both methods. One prototype pile was evaluated under traction-free and embedded conditions, and the other piles were evaluated under embedded conditions.

One of the test methods uses an impact on the side of the pile by a modal hammer to induce a low frequency flexural wave. The other test method uses a piezoelectric shaker mounted to the side of the pile to induce a high frequency wave. The pile response is measured with triaxial accelerometers mounted to the side of the pile. The piezoelectric shaker is computer-controlled to generate a force of specified amplitude, frequency, and duration.

The impact tests are analyzed to determine the phase velocity - frequency relationship, and to determine the group velocity and its frequency. The phase velocity is computed from the resonant frequencies identified on the acceleration spectrum of the recorded pile response. The group velocity is computed from the travel distance of the flexural wave and the return time between successive returns of the flexural wave. The frequency of the group is identified as the peak with the largest magnitude on the acceleration spectrum. The impact test generates waves that fall on the F(1,1) branch.

The controlled frequency results are analyzed to determine the group velocity and its frequency. One new prototype pile was tested under traction-free and embedded conditions and two existing prototype piles were tested under embedded conditions. The results were analyzed in the time domain and the frequency domain because the waves are dispersive. The analysis of the test results indicate that modes were excited on the F(1,1), F(1,2), F(1,3), and F(1,5) branches.

Indexing (document details)
Advisor: Finno, Richard J.
Commitee: Dowding, Charles H., Krizek, Raymond J.
School: Northwestern University
Department: Civil and Environmental Engineering
School Location: United States -- Illinois
Source: DAI-B 68/11, Dissertation Abstracts International
Source Type: DISSERTATION
Subjects: Civil engineering
Keywords: Concrete cylindrical piles, Deep foundations, Flexural guided waves, Nondestructive testing, Wave propagation
Publication Number: 3284190
ISBN: 9780549294672
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