Structural Modal Parameter Identification from Forced Vibration with Analytical Mode Decomposition

In this paper, a recently developed analytical mode decomposition method is proposed for modal parameters identification of structures subjected to impulsive, harmonic, and ambient excitations. The decomposed modal response for a structure subjected to an impulsive load is free vibration, thus, the instantaneous amplitude and phase angle of each decomposed modal response can be directly used to identify the modal parameters by using the least-squares fit procedure. For a structure subjected to a harmonic load, the transient response is first extracted from the measured response. Then, the extracted transient response can be decomposed into modal responses and the modal parameters can be evaluated. The proposed method in combination with the conventional random decrement technique is proposed for modal parameter identification for structures under ambient vibration. The random decrement technique is used to extract the free vibration information from which modal parameters are evaluated. A 3 degree-of-freedom mechanical system with closely-spaced modes subjected to impulsive, harmonic, and ambient loads is simulated as a numerical example. The new method is then validated with shake table testing of a 3-story building frame subjected to white noise and earthquake excitations. Both experiments and simulations showed high accuracy and effectiveness of the new method for structural modal parameters identification.