Modal Parameter Identification Of Girder Bridge Based On Stochastic Subspace Algorithm

Modal parameter identification based on Stochastic Subspace Identification (SSI for short) algorithm is one of the Modal parameter identification methods under the ambient excitation. Having theory reliability and engineering applied feasibility, the SSI method to identify large structure modal parameter is widely used in engineering for it can identify structure modal parameter in time domain only requiring output singnals and without needing artificial excitation. It is an important research aspect of the Modal parameter identification.First of all, the general research aspect and development trend of the modal paremeter identification is reviewed according to the conception of the modal parameter identification. The theoretical development of model parameter identification for bridge engineering is summarized, and the research meanings of damage identification based on it are also presented. And then the theoretical development and basic theory of modal parameter identification based on the ambient vibration are introduced. The conventional used methods in parameter identification based on the ambient excitation and the calculations of the eigenvalue and eigenvector of vibration system are introduced in detail. The basic theory of Stochastic Subspace Identification is introduced in Chapter 3. Stochastic Subspace Identification is a novel time domain identification method, which only uses ambient vibration response data to identify the system model by linear algebraic manipulations such as QR-factorization and Singular Value Decomposition (SVD) . The identification steps of Covariance-driven Stochastic Subspace Identification and Data-driven Stochastic Subspace Identification are introuduced in detail, Reference-based Stochastic Subspace Identification is mentioned, and the difference and relation of them is also presented.Subsequently, numerical verifications about Stochastic Subspace Identification algorithm are carried out. Taking a continuous girder bridge and a simple girder bridge as the examples, identification algorithm program based on MATLAB is carried out, making use of ANSYS to obtain modal information of the FE models and meanwhile add testing noise into consideration. This identification algorithm program also testifies feasibility, availability and applicability according to algorithms of the Stochastic Subspace Identification. The key of the Stochastic Subspace Identification algorithm are the dimensions of Hankel matrix and the ordering of the system. This paper uses Covariance-driven Stochastic Subspace Identification algorithm to identify girder bridge structure considering the effection on the identified result of system ordering.Finally, the main conclusions of this work and the questions that should be further discussed are figured out.