The Algorithm Study Of Modal Parameter Identification Based On Time-domain Algorithm And Damage Diagnosis In Bridges

The significance of structural healthy monitoring (SHM) of bridges has been paid more attention since the complxicity of bridges became the trend. The kernel of SHM of bridges goes to modal parameter identification of bridges, finite element model updating of bridges based on measured modal parameters, damge diagnosis of bridges. This study focused on couples of topics of the inverse dynamic analysis of bridges,(i) This study did some research on the application of modal parameter identification based on time-domain algorithm in practical bridges, and a practical arch bridge is taken as an example for verifying the effectiveness of ERA method and SSI method. The results showed that these two algorithms have strong ability to resist the influence of noise and it is promising for these two methods to solve the issues of identifying the modal parameters of practical bridges.(ii) To consider the effect of varying temperature on dynamic properties of bridge structures, a modal test for a arch bridge was carried out for about three months. Firstly, a long-term modal test is conducted, and the first six modes (frequencies, damping ratio and modal shapes) under different temperature are identified by modal parameter identification. Secondly, the comparison between the analytical dynamic properties and measured results are analyzed, and the changing regularity of this structure under varying temperature is summarized. The results show that the frequencies of this structure increase as the ambient temperature decrease, and that the damping ration and modal shapes are not sensitive with the ambient temperature. Finally, the relationship model between the environmental temperature and frequencies of this bridge model is obtained by regression analysis. The confidence interval of undamaged structure is obtained, and then this confidence interval is applied to assess the condition of this bridge.(iii) The minimum variance method based on sensitivity is employed to update the finite element model of a arch bridge. During the course of model updating some related aspects are also calculated including extracting the real mode shape, freedom expansion, model reduction, calculating sensitivities, choosing parameters for model updating. At last, the differences between measured and analytical modal parametes are reduced.(iv) With the development of sensor, signal acquiring and processing technologies, a larger number of vibration-based finite element model updating methods have been proposed for civil engineering structures. However, there are difficulties in applying these methods to real structures in operating environments. After a brief introduction to the vibration-based model updating methods developed over the last20years and their applications, this paper presents an analysis of the primary challenges in applying these model updating methods, and it concludes with a discussion of critical issues for future research in the area of vibration-based model updating methods.(v) A method combining the damge index and ANN (artificial neuro network) was proposed account on the damage detection of continous girder bridges. Firstly, the coefficients of AR model were obtained by time series analysis, which deemed as damage index. Secondly, the network considering many types damage was trained by using the damage index, and then this trained network could be applied to detect the damage of continous girder bridges. Finally, the effectiveness of proposed method was verified by using a numerical continous girder bridge.