Wind-tunnel tests of a large-scale sectional model with synchronous measurements of force and vibration responses were carried out to investigate the nonlinear behaviors of vertical vortex-induced forces （VIFs） on t...Wind-tunnel tests of a large-scale sectional model with synchronous measurements of force and vibration responses were carried out to investigate the nonlinear behaviors of vertical vortex-induced forces （VIFs） on three typical box decks （i.e., fully closed box, centrally slotted box, and semi-closed box）. The mechanisms of the onset, development, and self-limiting phenomenon of the vertical vortex-induced vibration （VlV） were also explored by analyzing the energy evolution of different vertical VIF components and their contributions to the vertical VIV responses. The results show that the nonlinear components of the vertical VIF often differ from deck to deck; the most important components of the vertical VIF, governing the stable amplitudes of the vertical VIV responses, are the linear and cubic components of velocity contained in the self-excited aerodynamic damping forces. The former provides a constant negative damping ratio to the vibration system and is thus the essential power driving the development of the VIV amplitude, while the latter provides a positive damping ratio proportional to the square of the vibration velocity and is actually the inherent factor making the VIV amplitude self-limiting. On these bases, a universal simplified nonlinear mathematical model of the vertical VIF on box decks of bridges is presented and verified in this paper; it can be used to predict the stable amplitudes of the vertical VIV of long-span bridges with satisfactory accuracy.展开更多
Stay cables in cable-stayed bridges are prone to large amplitude oscillations under external excitations.The vibration of the cables is predominantly measured by using accelerometers to measure the acceleration.The dy...Stay cables in cable-stayed bridges are prone to large amplitude oscillations under external excitations.The vibration of the cables is predominantly measured by using accelerometers to measure the acceleration.The dynamic displacement is then usually obtained indirectly from the double integration of the acceleration data.This paper reports an experimental method of measuring the displacement of stayed cables using a digital video camera.With the newly developed videogrammetric technique,the video clips are transferred into image frames,from which the shape and location of the target are identified.The displacement time history is then captured.The technique is applied to a cable-stayed bridge to measure the dynamic displacement of stay cables.The displacement is compared with the acceleration data in the frequency and time domains.The results show that the displacement measured by the digital video camera is comparable to the counterparts integrated from the acceleration data.The vibration frequencies identified from the acceleration are finally used to estimate the tension forces of the cables.The results show that the tension forces have insignificant changes after one year’s operation.展开更多
基金The work described in this paper was jointly supported by the National Natural Science Foundation of China （51478360, 51323013, and 50978204）.
文摘Wind-tunnel tests of a large-scale sectional model with synchronous measurements of force and vibration responses were carried out to investigate the nonlinear behaviors of vertical vortex-induced forces （VIFs） on three typical box decks （i.e., fully closed box, centrally slotted box, and semi-closed box）. The mechanisms of the onset, development, and self-limiting phenomenon of the vertical vortex-induced vibration （VlV） were also explored by analyzing the energy evolution of different vertical VIF components and their contributions to the vertical VIV responses. The results show that the nonlinear components of the vertical VIF often differ from deck to deck; the most important components of the vertical VIF, governing the stable amplitudes of the vertical VIV responses, are the linear and cubic components of velocity contained in the self-excited aerodynamic damping forces. The former provides a constant negative damping ratio to the vibration system and is thus the essential power driving the development of the VIV amplitude, while the latter provides a positive damping ratio proportional to the square of the vibration velocity and is actually the inherent factor making the VIV amplitude self-limiting. On these bases, a universal simplified nonlinear mathematical model of the vertical VIF on box decks of bridges is presented and verified in this paper; it can be used to predict the stable amplitudes of the vertical VIV of long-span bridges with satisfactory accuracy.
基金Supported by the Research Grants Council of the Hong Kong Special Administrative Region of China(No.PolyU 5298/11E)the Hong Kong Polytechnic University(No.A-PD0H).
文摘Stay cables in cable-stayed bridges are prone to large amplitude oscillations under external excitations.The vibration of the cables is predominantly measured by using accelerometers to measure the acceleration.The dynamic displacement is then usually obtained indirectly from the double integration of the acceleration data.This paper reports an experimental method of measuring the displacement of stayed cables using a digital video camera.With the newly developed videogrammetric technique,the video clips are transferred into image frames,from which the shape and location of the target are identified.The displacement time history is then captured.The technique is applied to a cable-stayed bridge to measure the dynamic displacement of stay cables.The displacement is compared with the acceleration data in the frequency and time domains.The results show that the displacement measured by the digital video camera is comparable to the counterparts integrated from the acceleration data.The vibration frequencies identified from the acceleration are finally used to estimate the tension forces of the cables.The results show that the tension forces have insignificant changes after one year’s operation.
