Experimental Modal Analysis Of Cable-stayed Arch Bridge Model And Research On The Influences Of Cable On Modal Parameters

Cable-stayed arch bridge is a new type of composite bridge which has taken advantage of both cable-stayed bridge and arch bridge. Its integral structure mechanical performance and especially dynamic performance appear more complicated. However, dynamic behavior, which is the foundation to carry out the analysis of structure vibration response, seismic resistant, stability of wind resistant, is the important aspect of bridge dynamic mechanical problem. In order to validate the theory in such a complicated structure, only the theory research is insufficient and the experiment research is also extremely necessary. And further more, the modal parameters identified in the system are available to recognize and predict the damage in the structure and provide the basis for the optimum design of structure dynamic characteristics. Under the above background, this paper conducts the experiment mode analysis of cable-stayed arch bridge, and main accomplishments are listed as follows:(1)The dynamic similarity criterion of Xiangtan Xiangjiang river has been analyzed by similarity theory; Similarity ratio of each modal parameters has been obtained by modal analysis theory; In addition, similarity relationship of real model which approximately satisfies dynamic similarity has been further investigated, and the similarity ratios of each ideal parameter to actual modal parameter have been gained. Finally, three kinds of models: real bridge, ideal model and theory model are established in finite element analysis software ANSYS. Their modal parameters and similarity ratios have been calculated and obtained, which validates above-mentioned relationships of mode parameters and similarity ratios.(2)According to the procedure of experiment modal analysis, choosing appropriate excitation mode and the sensor and adjusting the system, the paper obtains time signals of every test points using the sampling technique of modal separation excitation and time base variation. And then the paper employs estimation of transfer function in the frequency-domain signals which are converted from FFT. Finally, the paper fits modal parameters of system through the frequency-domain method.(3)Impulse response function is obtained through the IFFT transformation of the transfer function. And then the modal parameter is calculated through characteristic Economy Realization Arithmetic of time base method (ERA), which is compared with the modal frequency obtained from the method of frequency domain. The MAC is used to validate vibration mode of model.(4)Experimental modal analysis of 8 working conditions is conducted: the tension of the cables is changed in order to study the effect of the variation of the cable's tension on the structure mode parameter; The number of the cables is gradually reduced to zero, so as to study the effect of the existence and density of cable on the mode parameters. In addition, according to the effect of the cable on the mode parameters, some suggestions are proposed.