An Improved Random Decrement Algorithm with Time-Varying Threshold Level for Ambient Modal Identification

Conference paper
Part of the Lecture Notes in Electrical Engineering book series (LNEE, volume 293)


Modal Identification from response data only is studied for structural systems under nonstationary ambient vibration. The topic of this paper is the estimation of modal parameters from nonstationary ambient vibration data by applying the random decrement algorithm with time-varying threshold level. In the conventional Random Decrement Algorithm, the threshold level for evaluating randomdec signatures is defined as the standard deviation value of response data of the reference channel. However, the distortion of randomdec signatures may be induced by the error involved in the noise obtained from the original response data in practice. To improve the accuracy of identification, a modification of the sampling procedure in random decrement algorithm is proposed for modal-parameter identification from the nonstationary ambient response data. The time-varying threshold level is presented for the acquisition of more sample time history to perform averaging analysis, and defined as the temporal root-mean-square function of structural response, which can appropriately describe a wide variety of nonstationary behaviors in reality. Numerical simulations confirm the validity and robustness of the proposed modal-identification method from nonstationary ambient response data under noisy conditions.


Modal identification Nonstationary ambient vibration Random decrement algorithm Time-varying threshold level Temporal root-mean-square function 


  1. 1.
    Cole, H. A., Jr. (1971). “Method and apparatus for measuring the damping characteristics of a structure.” United States Patent No. 3, 620, 069, Google Scholar
  2. 2.
    Lin, C. S., & Chiang D. Y. (2013). Modal identification from nonstationary ambient response data using extended random decrement algorithm. Computers & Structures, 119, 104–114.Google Scholar
  3. 3.
    Ibrahim, S. R., & Mikulcik, E. C. (1977). A method for the direct identification of vibration parameters from free response. Shock and Vibration Bulletin, 47(4), 183–198.Google Scholar
  4. 4.
    Chiang, D. Y., & Lin, C. S. (2008). Identification of modal parameters from nonstationary ambient vibration data using correlation technique. AIAA Journal, 46(11), 2752–2759.CrossRefGoogle Scholar
  5. 5.
    Shinozuka, M., & Jan, C.-M. (1972). Digital simulation of random processes and its applications. Journal of Sound and Vibration, 25(1), 111–128.CrossRefGoogle Scholar
  6. 6.
    Newmark, N. M. (1959). A method of computation for structural dynamics. Journal of Engineering Mechanics, ASCE, 85(EM3), 67–94.Google Scholar

Copyright information

© Springer International Publishing Switzerland 2014

Authors and Affiliations

  • Chang-Sheng Lin
    • 1
  • Tse-Chuan Tseng
    • 1
  • Din-Goa Huang
    • 1
  1. 1.Precision Mechanical Engineering Group, Instrumentation Development DivisionNational Synchrotron Radiation Research CenterHsinchuTaiwan, Republic of China

Personalised recommendations