Stochastic Subspace Identification And Application Of Struetures Under Ambient Vibration

Civil engineering structure is an important part of national infrastructures that is directly related to people's daily life. It is required to understand their dynamic properties during the inspection, assessment and health monitoring of civil engineering structures. Structural modal parameters reflect the dynamic properties that can be obtained by either traditional or ambient vibration identification techniques. Dynamic testing of civil engineering structures under ambient vibration excitation has many advantages, such as no excitation equipment needed, no interruption of structural service conditions and less test time, which is more close to the real working conditions of civil engineering structures. As only output is measured and real input remains unknown in terms of ambient vibration testing, the modal parameter identification will therefore need to base itself on output-only data. The output-only modal parameter identification is different from the traditional one that is based on both input and output datas. The main work and conclusions include:(1) Ambient vibration experiment of a space frame model in this paper. Fistly, The stochastic subspace identification method in time domain is used for the modal identification, and the dynamic character of the model is analyzed by the Finite Element Model (FEM) obtain the model resonant frequencies and model shapes . Secondly the stochastic subspace identification method in time domain was used for the modal identification. We can gain the data of experiment using transducers, the data acquisition system and post treatment of the data. The finite element model is validated to match the testing natural frequencies and mode shapes of the model.(2) Considering all modal parameters of the structure, inherent frequency is the easiest one to be acquired and the highest precision. In the paper, we put forward a new damage detection method—moving mass method with repeated detections. The method makes measurement to the structure several times while using moving mass block in different locations, and only use frequency data according to each measurement to determine structure damage. The method improve structural identification precision. Meanwhile, structural moving mass detection method realizes the aim of determining structural damage model frequency only with structural low order model frequency, even the first order, and it also provides a simple method of practical detection for structure in one working state.(3) The flexibility matrix method for damage identification of frame structure is suggested in this paper. The first modal parameters obtained by dynamic measuring are needed only in this method. Vibratory residual vectors are used for damage of the frame structure, and according to the locations of damage the structure we can identified by the maximum value of flexibility matrix .It is indicated by a testing of frame model damage identification that only low-order modal parameters are needed to identify a structural damage effectively.