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Technical Briefs

Application of Modal Identification Methods to Spatial Structure Using Field Measurement Data

[+] Author and Article Information
Wei Liu

Department of Astronautic Science and Mechanics, Harbin Institute of Technology, Harbin 150001, Chinaliuweiliuwei2005@gmail.com and liuweiliuwei2003@hit.edu.cn

Wei-cheng Gao

Department of Astronautic Science and Mechanics, Harbin Institute of Technology, Harbin 150001, Chinagaoweicheng@sina.com

Yi Sun

Department of Astronautic Science and Mechanics, Harbin Institute of Technology, Harbin 150001, Chinasunyi@hit.edu.cn

J. Vib. Acoust 131(3), 034503 (Apr 22, 2009) (10 pages) doi:10.1115/1.3085881 History: Received January 23, 2008; Revised December 10, 2008; Published April 22, 2009

Modal identification with output-only measurements plays a key role in vibration-based damage detection, model updating, and structural health monitoring in civil engineering. This paper addresses the application of modal identification method to a triangle steel tube truss natatorium using the field measurement data. To obtain dynamic characteristics of the spatial structure, four different output-only system identification methods are employed. They are natural excitation technique–eigensystem realization algorithm, data-driven stochastic subspace identification method, frequency-domain decomposition/frequency-spatial domain decomposition method, and half spectra/rational fractional orthogonal polynomial method. First an analytical modal analysis was performed on the three-dimensional finite element model according to the factual layout design to obtain the calculated frequencies and mode shapes. Then the whole procedure of the field vibration tests on the natatorium was presented. Finally, practical issues and efficiency of the four output-only modal identification techniques are investigated, and compared with the results from a finite element model. The system identification results demonstrate that both methods can provide reliable information on dynamic characteristics of the spatial structure. The frequency-domain methods, however, can quickly identify the modal parameters, but the leakage error introduced by power-spectral density estimation is existent due to the limited length of data. And the time-domain methods can avoid the leakage error, but the computational modes and the computational cost are the main two drawbacks in application. The conclusion is that several system identification methods should be consulted to ensure the accuracy of the estimated modal parameters.

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Structural layout plan of the natatorium (units: mm)

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Figure 2

View of the natatorium

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Figure 3

Finite element model of the whole structure

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Figure 4

Mode shapes of the whole structure calculated by FEM

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Figure 5

Sensors in field vibration test

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Figure 6

Frequency-domain analysis of some typical time-domain signals

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Figure 7

Stability diagram obtained by the NExT-ERA algorithm

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Figure 8

Stability diagram obtained by the SSI-DATA algorithm

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Figure 9

Six natural frequencies identified by the FDD algorithm

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Figure 10

The fitted results obtained by the RFOP algorithm

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Figure 11

Identified mode shapes by the NExT-ERA algorithm

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Figure 12

Identified mode shapes by the SSI-DATA algorithm

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Figure 13

Identified mode shapes by the FDD/FSDD algorithm

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Figure 14

Identified mode shapes by the RFOP algorithm

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