Large Span Cable - Bridge Coupled Vibration Analysis And Experiment

Several cable-stayed bridges all over the world ever suffered the stay cable oscillations conjugated with simultaneous vibrations of the deck, which have a significant effect on the service life of cables and safe operation of bridges. Compared with the vibration mechanism of a single cable subjected to direct excitation, the dynamic mechanism of cable-deck interaction is more complicated. Hence, little research regarding cable-deck interaction can be found. Under these circumstances, it is the purpose of the current thesis to analyze and identify experimentally the cable-deck interaction in large span cable-stayed bridges. This research is valuable in terms of theoretical analysis and engineering application. The main research outcomes are presented as following:The analytical model of cable-deck interaction in large span cable-stayed bridges is simplified to be a simple model that a hanging cable is subjected to the harmonic oscillation of its supports, corresponding to harmonic movement of the deck. Nonlinear equations of motion are formulated for this simple model by means of the Hamiltonian principle. Base on the numeric example of the C14 stay cable of Zhanjiang Bay Bridge solved by Runge-Kutta method, a couple of factors effecting stay cable parameter vibration are studied.The further work bases on the Zhanjiang Bay Bridge, a cable-stayed bridge with a main span of 480m. Two types of numerical models are developed, which are designated as OECS and MECS. The OECS is a finite element model of the Zhanjiang Bay Bridge that idealizes each stay as a single truss element. By contrast, the MECS idealizes each stay cable as a series of truss elements. By comparing the dynamic parameters obtained on the basis of the OECS and MECS models, how the mechanical characteristics influence the occurrence of cable-structure interaction is investigated. The cable-deck interaction of Zhanjiang Bay Bridge is also investigated by means of numerical finite element modeling. The bridge response to two sinusoidal point loads, the frequencies of which are set to that of the 2nd and 3rd vertical mode of the global modes respectively, and random excitation is numerically evaluated. The numerical results show the existence of dynamic interaction between the stay cables and the deck. What's more, a peak factor is proposed to evaluate different levels of cable-deck interaction.The ambient vibration on-site measurements of Zhanjiang Bay Bridge are developed with the purpose of identifying the bridge frequencies and also the frequencies of cables. Various dynamic interactions between cables and deck are deeply discussed based on the frequencies indentified. Furthermore, additional on-site test campaigns are developed to investigate the dynamic interaction between the cables, which are revealed to be extremely prone to cable-deck interaction, and deck. It is possible to confirm the occurrence of the cable-deck interaction in Zhanjiang Bay Bridge by comparing the peak factor of several adjacent cables as well as the peaks of auto-power spectra of the acceleration time histories, which further evidences the existence of the phenomenon of cable-deck interaction in large span cable-stayed bridge.