Nonlinear Static Analysis Of The Cables And Research Of The Rain-wind-induced Vibration In Cable-stayed Bridge

As a kind of flexible composite structure system, Cable-stayed bridge shows itsremarkable advantages in many aspects, which had been built widely all over the world. Withits own tension, the cable, as one of the most important bearing component structure,coordinated the whole structural system perfectly, so that it is always in a state of stableequilibrium. Therefore, analysis of the status of the cable is very important to study themechanical properties of the whole structural system.Because of its flexible characteristics, in the dead weight and under the action of axialforce, the space form of the cable assumes a catenary line. As well as the increasing of thespan in modern cable-stayed bridge, the length of the cable increase gradually. It is bound toamplify the flexibility, and make all kinds of nonlinear factors more significantly. At the sametime, considering its lighter weight and low structural damping, the cable itself could vibrateeasily under stimulus of external factors. In all kinds of cable vibrations rain-wind-inducedvibration is undoubtedly the severest one. Taking xiangshan-harbor highway bridge as theengineering background, in this paper, we’ll research the cable’s problems including staticconfiguration, nonlinear mechanical characteristics and the rain-wind-induced vibrationin-depth.1. Summarize various analytical expressions of the cable’s static configuration, included theparabola and the catenary theory. Conclude the computational formula of the unstressed cablelength, then verify all these formulas above through the case of the xiangshan-harbor highwaybridge. The precision of the solution with parabola theory is accurate enough to meet theneeds of the project, however, the error will increase rapidly along with the decrease of thecable’s tension.2. Study the causes of geometric nonlinear effect of the cable, such as "sag effect" and"large displacement effect", then analysis and expound the ideas and solutions to theseproblems with the theory of finite element. Establish the finite element model in space basedon the finite element program "ANSYS", and change different parameters to research themain factors which influence the nonlinear characteristic of the cables. From thesecalculations we can conclude that, to the same cable, the angle offsets could only make a linear change of the internal force, but the axial force was the essential factor which lead tothe nonlinear change of the internal force.3. Based on the quasi-steady assumption, the change of the cable’s posture in space isconsidered to establish the rigid segmental model of the inclined cable with rivulet on it, anddeduces the nonlinear vibration differential equation of the cable and the rivulet. Finally, usethe Runge-Kutta method to write the matlab program to solving the nonlinear system ofdifferential equations, then get the response of the cable’s vibration in wind and rain, andexplains the mechanism of its generation and development. The results indicated thatrain-wind-induced vibration of stay cables refers to a kind of violent oscillation phenomenonwhich is induced by surface rivulet’s influence on the aerodynamic shape of stay cables. Thisphenomenon existed with obvious feature of "speed limited" and "amplitude limited"; and it ishighly sensitive to the change of damping; So according to this characteristic, we could putforward the corresponding measures to restrain the vibration.