Mode shape identification based on monophotogrammetry and relative displacements of partial structures under ambient excitation

Traditional mode shape identification methods are based mostly on acceleration responses, and many hardware devices must be installed. On the basis of monophotogrammetry, the dynamic displacement responses can be measured, which is more economical and efficient. However, because of the localization of photogrammetry, accurate measurements of absolute displacements are difficult, and the relative dynamic displacements of partial structures are a better choice. The partial structures represent a part of the structure, such as two floors of a building or the segment of a beam structure. Hence, a new mode shape identification method based on monophotogrammetry and the relative dynamic displacements of partial structures is proposed in this paper. First, the partial structure is defined, and the selection requirements for partial structures are introduced. Moreover, the relative displacements for each partial structure are defined. Second, a relative displacement measurement method for each partial structure is proposed using monophotogrammetry. Then, the power spectral density matrix can be reconstructed using Fourier spectra of these relative displacements, and the modal shapes can be extracted using singular value decomposition. Finally, the proposed method is verified using a laboratory plane frame under white noise excitation. The results show that the proposed method can effectively extract the mode shapes using monophotogrammetry and the relative displacements of partial structures.