Influence Of Mass And Damping Parameters And Turbulence On Galloping And Vortex-induced Vibration Of H-shape Hanger

In the past ten years,the construction of long-span steel arch bridges in China has developed rapidly.Hshape hangers have been widely used in the construction of arch bridges due to factors such as ease of manufacture and construction.However,the H-shape hanger has the characteristics of large slenderness ratio,blunt section and small damping.It is often extremely poor in aerodynamic stability,and it is easy to generate vortex-induced vibration and galloping under the action of wind,which results in fatigue damage or even short-term damage of components,affects the service life of bridges and even endangers the safety of the whole bridge.In this paper,the following research is carried out on the common H-shape hanger structure in bridges:(1)In order to study the influence of structural damping ratio change on the cross-wind galloping and vortex-induced vibration of H-shape hanger,a new type of damper is designed based on the principle of electromagnetic induction,which is convenient to continuously adjust the structural damping ratio of Hshaped hanger without introducing additional stiffness and nonlinear effects,it is found that increasing the damping ratio can effectively suppress the hard galloping.But it has little effect on the soft galloping in little damping ratio range.Only when the damping ratio is increased to a certain extent can it be effectively suppressed.The vortex-induced vibration amplitude decreases exponentially with increasing damping ratio.(2)In order to study the influence of structural dimensionless mass on the cross-wind galloping and vortex-induced vibration of H-shape hangers,five sets of wind tunnel tests with different mass ratios were carried out.The study found that the mass ratio was increased within a small range.,the impact on the vibration is not large or the galloping wind speed displacement curve is shifted to a higher wind speed.Only when the mass ratio is increased to a certain extent can the vibration be effectively suppressed;increasing the mass ratio can reduce the vortex-induced vibration amplitude but also make the locked wind speed interval of vortex-induced vibration translate to a lower dimensionless wind speed.The galloping and vortexinduced vibration responses of H-shape hangers with different damping ratios and mass ratios are not the same.Therefore,it is not appropriate to describe the mass damping of H-shape hangers with only one Scruton Number in a certain range.(3)The turbulent wind field with different turbulence intensity and turbulent integral scale is simulated in the wind tunnel through the passive grid.The wind tunnel vibration test of the H-shaped hanger is carried out.The results show that the turbulent intensity decreases exponentially with the increase of test wind speed,while the turbulent integral scale increases in a power function way with the increase of test wind speed;the turbulent wind field can suppress galloping amplitude,increases the vortex-induced vibration amplitude and even excites the vortex-induced vibration that does not appear in the uniform flow.(4)By measuring the static three-component force coefficient of the H-shape hanger,the galloping force coefficient and the galloping critical wind speed are calculated according to the galloping quasi-steady theory.The study finds that galloping occurs at all angles of attack with negative galloping force coefficients in uniform flow field with small damping ratio,but galloping occurs at some angles of attack with positive galloping force coefficients too.When the damping ratio exceeds 0.3%,comparing with the experimental value,the galloping critical wind speed is also dangerous.Therefore,the theory of the galloping quasi-steady theory is not completely applicable to H-sections.(5)Through the pressure measurement test of the static flow state,the galloping state and the vortexinduced vibration state of the H-shape hanger,the average wind pressure coefficient and the pulsating wind pressure coefficient of each measuring point are calculated,and the data are processed by integration and FFT transformation.The aerodynamic lift time history and frequency spectrum of the model are obtained.The reason of wind vibration of the model is explained from a more microscopic aerodynamic perspective.