1. Practical use of FRF in system identification -------under ambient excitation Presenter: Yuting OUYANG Mentor: Weixing SHI Department: RISEDR

2. Outlines Introduction Basic Theory Pre-analysis Numerical & Experimental example

3. Introduction Identification method: Time domain; Frequency domain One efficient and effective way is PSD in identifying linear system Aim: Establishing an integral module of FRF in SVSA(Shock and Vibration Signal Analysis system) for practical use of system identification under ambient vibration in future. System Signal LinearNonlinear StationaryIII NonstationaryIIIIV

4. Basic Theory A linear system, with proportional damping assumption, FRF and its inverse Fourier transformation are as follows: Linear system: Superposition principle; Stationary: Global time-frequency transformation (ambient excitation) Worden, K., Tomlinson, G.R. Nonlinearity in Structural Dynamics: Detection, Identification and Modeling[M].

5. Pre-analysis Ambient excitation; (white noise, stationary color noise) Window type; (Rectangular, Triangular, Hamming, Hann, Blackman) Resolution; Measurement Noise; Shan J, Shi W, Wang J. Regional study on structural dynamic property of buildings in China[J].

6. a) According to former theory of FRF, its easy to obtain the amplitude and phase figure. Numerical analysis

7. b) According to the former results of FRF, it is easy to get the modal shape and damping ration. Numerical analysis

8. a) Take Four-Story Reinforced Concrete and Post-Tensioned E-Defense Building Tests as an experimental example; (Case: Kobe 25%) Experimental analysis

9. Floor Frequency(Hz)Sin(Phase) 1st2nd1st2nd 1 2.12408.3496 -0.74730.2834 2 -0.82920.2566 3 -0.84180.5223 4 -0.8501-0.2961 Std(|X|)000.0473 0.1229 b) Considering structure with a uniform distribution of stiffness; Experimental analysis

10. c) Considering uncertainties;

11. FRF Module (Platform: Visual Studio 2010; Language: VB)

12. Thanks