Experimental Study On Nonlinear Vibration Modes Of Cable-stayed Bridges

Nonlinear vibration of cable-stayed bridges has always been a research hotspot in the field of bridge engineering.In order to reveal the mechanism of large-scale vibration of cable-stayed bridges,the refined model of cable-stayed bridges is tested in this paper.Firstly,the reliable modal parameters of cable-stayed bridges are obtained by modal analysis of cable-stayed bridges through experiments and two kinds of finite element models.Then,a single harmonic load is applied near the mid-span of the cable-stayed bridge to study the non-linear vibration mode and mechanism of the cable,and the non-linear vibration characteristics of the cable are further explained by sweeping frequency test.Finally,the coupled vibration between two cables,as well as cable and beam,is studied by free vibration test and forced vibration test.The specific work of this paper includes the following aspects:(1)The modal analysis of cable-stayed bridge model is carried out.Firstly,the cable force of cable-stayed bridge model is measured.On this basis,considering the non-linear factors such as cable sag,two kinds of finite element models,OECS(One-Element Cable-Stay)and MECS(Multiple-Elements Cable-Stay),are established to carry out modal analysis of cable-stayed bridge.Then,the results are compared with the experimental modal analysis results,and reliable modal parameters are obtained.Finally,based on the results of MECS modal analysis,the nonlinear vibration of cable-stayed bridge is analyzed.(2)Simple harmonic excitation is applied near the mid-span of the main girder of the cable-stayed bridge model.The excitation frequency includes the first two in-plane vertical bending modal frequencies of the main girder and the basic frequency of the cable and etc.The results show that when the vertical excitation frequency is proportional to the frequency of cable or girder,the main resonance of girder,and forced and parametric vibration,superharmonic resonance,subharmonic resonance,principal resonance and multiple internal resonance of cable are observed.(3)The frequency sweeping test is performed on the cable-stayed bridge,and the frequency range is 4.3 Hz to 6.4 Hz.The research shows that due to the nonlinearity of the stay cable,the "soft spring" characteristics is observed,and the curves of sweep-up and sweep-down do not coincide completely;there are multiple peaks in the amplitude-frequency response curve of the stay cable,including the forced and parametric vibration caused by main resonance of main girder,main resonance and other coupled vibrations.At the same time,it is observed that the amplitude of the full-bridge vibration caused by is larger than the local vibration amplitude of the stay cable.Therefore,in the design of the cable-stayed bridge,it is necessary to give priority to avoid such full-bridge vibration.(4)The coupled vibration between the members of the cable-stayed bridge is studied by free vibration and forced vibration test.The test shows that there are two forms of coupled vibration,one is that the vibration frequencies of the two components interact with each other.The "beat" vibration can be observed and it is found tha t time history curves of two members are synchronous.The other is that the peaks and valleys of the time-history curves of the two components are interlaced,and there is obvious energy exchange between the two components.