Study On Wind-induced Vibration Characteristics Of Two Classes Of Bridge Components With Large Slenderness Ratio

The wind-induced vibration characteristics of two classes of structural elements with large slenderness ratio that are frequently used in the bridge are studied in this paper. The first of them is H-shaped and rectangular section members that are often applied in the long span arch bridge and truss bridge. The suspenders of arch bridge with these two sections subject to large wind attack angle are chosen to study the wind-induced vibration characteristics. The other kind is cable with circular section that is commonly used in the suspension bridge and cable stayed bridge. The aerodynamic interference mechanism between the upstream and downstream main cables without suspenders is investigated. Some main contributions in this paper are as follows:1. The torsional flutter theory of vertical H-shaped member for the large wind attack angle is developed based on the theoretical research and wind tunnel tests. It is proved that the observed wind-induced vibration of suspenders in one long span arch bridge is torsional flutter rather than vortex-excited resonance. The slots of web can't increase the flutter critical wind speed, but it is helpful to improve the characteristics of galloping and vortex-induced vibration by modest slot ratio. The wind-induced vibration characteristics of suspender with different height-width ratios, web and flange plate slot ratios are evaluated by 16 groups of orthogonal tests. The variance analysis theory is used to illustrate the effects of the three parameters in the flutter, galloping and vortex-induced vibration of suspender. Reasonable change of section can effectively enhance the onset wind velocity of flutter, galloping and vortex-induced vibration, and decrease the lock-in wind speed range of vortex-induced vibration as well as the amplitude of vortex-induced vibration.2. Wind tunnel tests has shown that suspenders with rectangular section have excellent stability of torsional flutter; but facing some other problems such as lower critical wind speed of galloping, rather larger amplitude and lock-in wind speed range of vortex-induced vibration. Therefore, covering the inner-surface of suspender with extra damping layer is presented to control wind-induced vibration. The model test is used to verify the feasibility of this control strategy. Furthermore, the damping characteristics of suspender with damping layer are evaluated by numerical simulation. 3. The forced vibration equipment with three degrees of freedom is applied to solve the distortion problem of vertical motion in free elastic suspension method, and the flutter derivatives of H-shaped and rectangular sections under large attack angle are accurately identified from the forced vibration testing data. The comparative study shows that the distortion of vertical motion will lead to the identification error of flutter derivatives, and the error increases with the angle of attack. Therefore, the forced vibration method of identifying flutter derivatives with large attack angle is confirmed to have excellent performance. The aerodynamic forces of section model are measured by the force balance of forced vibration equipment, which is further used to estimate the Strouhal number of H-shaped and rectangular sections, and the measurements of steady aerodynamic force coefficient continuously varying with attack angles are realized. All these work have extended the application field of force vibration method.4. The wind resistant design formulas of commonly used H-shaped and rectangular structural elements with large slenderness ratio are derived to define the upper limit of the practical length of these elements. Meanwhile, some suggestions of wind resistant design are given.5. The aerodynamic interference between two parallel main cables is studied by combining aeroelastic model tests with computational fluid dynamics (CFD) technology. Wind tunnel tests have shown that wake galloping with stronger out-plane than in-plane vibration can be seen in the downstream main cable, and the distance between the upstream and downstream main cables, wind yaw angle, wind attack angle as well as natural frequency of cable have a great influence on the critical wind velocity of wake galloping. CFD simulations have indicated that Reynolds number doesn't have effect on the trend of changes in across-wind force, and moreover, the critical wind speed of wake galloping of prototype and model with corresponding Reynolds number is a little bit higher than that in the model tests.