DIC-Based Operational Modal Analysis Of Bridge Structures

It is of great significance to obtain structural dynamic characteristics through modal analysis for health monitoring of bridges.The traditional modal method is to arrange sensors on the surface of the structure to measure the vibration signal,and adopt the EMA(Experimental Modal Analysis)theory to obtain the frequencies,damping ratios and mode shapes of the bridge structure.There are often two main problems during this kind of experiment.Firstly,the sensors cannot be placed on every node of the structure,it may lead to incomplete mode data.Secondly,the excitation cost is high.It may affect the structure routine operation,and even cause structure damage.In this paper,DIC technology and OMA theory are combined as a new method of bridge modal analysis to solve the above problems.As a new optical measurement technology,DIC is validated to be effective when applied to acquire vibration signals.The following experiments are set up to evaluate the performance of DIC.Firstly,the measurement results,including the shape characteristics and analysis results of the signal,of the sensor and DIC measurements are compared.The comparisons showed good practicability and accuracy of DIC technology.Then,the effects of shooting distance and vibration amplitude are discussed.Vibration measurement is carried out under different shooting distance and amplitude conditions.There is some interference in the signal results measured by DIC under far shooting distance or small amplitude,and some ideas and results are given.OMA is often used in the structural vibration analysis under ambient excitation.In this paper,several common OMA theories and their effects are studied.Firstly,the modal information of the experimental model is analyzed from the FRF.Then,some other methods like PSD,RT,RDT,NEx T,ERA and ARMA are derived and applied to process the same data.It's found that the modal results obtained by different methods are highly consistent,which validates the reliability of the analysis results.The results in this paper are helpful to promote the application of dynamic characteristics identification method in structural damage detection.With the practical problems fully considered,DIC-based OMA method is proved to be a good way to deal with modal analysis for bridge structures.Furthermore,some problems in DIC measurement results are found,and the solutions are put forward.Various analysis results by different OMA theories are compared,which is helpful to provide more research materials for structural analysis.