Mechanism Investigation On The Wake-induced Vibration Of The Hangers Of Suspension Bridges Based On Vibration Measurement Of Sectional Models

As the span of a suspension bridge continues to increase,the length of the hanger is getting longer.Because of the low frequency,low damping,and light weight,suspension bridge hangers can easily undergo significant vibration under the effects of wind loads,vehicle loads,etc.This will shorten the fatigue life of the hangers,thereby affecting the safety and durability of the entire bridge.According to available data,there have been significant wind-induced vibrations of cable structures on several suspension bridges at home and abroad,including the Great Belt East Bridge in Denmark,the Akashi Kaikyo Bridge in Japan and the Xihoumen Bridge in China.There are many causes of wind-induced vibration of cables in suspension bridges.Through wind tunnel tests and theoretical analysis methods,the wake-induced vibration mechanism between cable strands of suspension hangers was studied.The main research content is as follows:(1)A smooth-rigid segment model(simulated parallel steel wire hanger)with double strands was made,and a two-dimensional segment model vibrating wind tunnel test was conducted for the suspension bridge hangers with multiple working conditions.The wake-induced vibration range of wake cables was obtained.On this basis,the law of motion response of the downstream cable strand was measured,and the influence of wind speed and structural damping ratio o n the wind-induced vibration of downstream strands was studied.The results show that in the spatial range of X?5.25 and Y?1.5,the downstream cable-strand can generate large wake-induced vibrations.The vibration modes include two types: linear motion with one degree of freedom and elliptical motion with two degrees of freedom.The frequency of motion is slightly greater than and less than the structural natural frequency,respectively.Wind speed has a significant effect on the movement law of the downstream cable strands;the increase in damping ratio can increase t he starting wind speed,but has little effect on the magnitude of the amplitude.(2)A rough-rigid section model(simulated wire rope hanger)with double strands was produced,the vibration measurement wind tunnel of two-dimensional segment model was conducted for the suspension bridge cable in multiple conditions.In order to compare the test results,the vibration measurement wind tunnel test of glossy cable strand under the same experimental conditions was performed.The wake-induced vibration range of downstream strands was obtained.The law of motion response of the cable strands was measured,and the parameter analysis of wind-induced vibration of wake strands was done.The results show that the space range of large wake-induced vibration generated by rough cable strands is smaller than that of smooth cable strands.There are only two degrees of freedom elliptical vibration in a rough cable strand.Its stable motion frequency is less than the natural frequency of the structure,and there is a significant aerodynamic negative stiffness effect.The influence of wind speed and structural damping ratio on the rough strands is similar to that of smooth strands.(3)Based on the quasi-steady theory,the motion response law obtained by numerical simulation is compared with the test,and then the mechanism of wake excitation is studied from the perspective of energy.The results show that the theoretical model based on quasi-steady theory can obtain the elliptical motion response,which is in good agreement with the experimental results.In one exercise cycle,the work done by the aerodynamic stiffness force is positive.The work done by the aerodynamic damping force is negative,which indicates that the downstream cable strand elliptical motion is driven by the negative aerodynamic stiffness force,which is consistent with the frequency domain characteristics of the downstream strand in the wind tunnel test.