Signal Separation Method for Tower Mode Shape Measurement
Publication: Journal of Structural Engineering
Volume 115, Issue 3
Abstract
Vibration shapes of the fundamental modes of eight‐legged, K‐braced, offshore towers undergo significant changes when important braces are damaged. These changes, measurable at deck‐level, provide valuable clues for detecting damage. Because of the small difference between vibration frequencies of the two fundamental translational modes in these towers, the mode shapes are difficult to measure. A simple method is presented which solves this difficulty. The method uses transient acceleration response records that can be produced by different excitation procedures, and no knowledge of the input that causes the excitation is necessary. The finite Fourier transform of such records is examined, and its important properties are pointed out for low damping. Based on these properties, procedures are set forth by which mode shape data can be retrieved from closely spaced peaks in response spectra. The retrieval is done by separating these peaks from each other. Applications of the method in a numerical experiment, and in a physical experiment on a l/50th scale offshore platform model, are presented. Application of the method to full‐scale towers is discussed.
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Information & Authors
Information
Published In
Journal of Structural Engineering
Volume 115 • Issue 3 • March 1989
Pages: 707 - 723
Copyright
Copyright © 1989 ASCE.
History
Published online: Mar 1, 1989
Published in print: Mar 1989
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