Experimental Study On Vortex Vibration Performance Of Fabricated Box-Section Crosswalk

In recent years,with the adoption of high-strength materials and cable carrying systems,the design of the footbridge tends to be soft and soft,resulting in a decrease in the natural vibration frequency of the structure,resulting in an increase in the sensitivity of the structural response to natural wind.Compared with other forms of wind-induced vibration,the bridge is more prone to vortex vibration under the action of the wind.Although it does not cause catastrophic damage,its frequency and frequency are high,which will cause the local components of the bridge to be larger,and the alternating stress causes the fatigue damage problem.At the same time,excessive eddy vibration amplitude will also bring uncomfortable feelings to pedestrians.Based on the above two reasons,based on the typical main beam section of the footbridge and several types of pedestrian bridge structures,the segmental model wind tunnel test is used to systematically study the vortex vibration characteristics and pedestrian comfort evaluation of the footbridge.The main contents and conclusions are as follows:(1)The vortex-induced resonance characteristics of six kinds of footbridge segment models are obtained by wind tunnel test.The test results show that the amplitude of the vortex vibration of the R1 main beam with the pick arm at the negative angle of attack is greater than that at the positive angle of attack.The vortex amplitude increases with the increase of the width-to-height ratio of the main beam,but the vortex wind speed interval does not change much with the increase of the main beam width;The vortex-vibration amplitude of the closed stream-like box girder R2 main beam is larger at the Angle of attack,and decreases with the increase of the girder width-to-height ratio.However,the vortex-vibration wind speed range does not change much with the increase of girder width.(2)Based on different vortex force models,the conversion relationship between the vortex amplitude of the segment model and the vortex amplitude of the real bridge is studied.Considering the damping correction,the amplitude obtained by the wind tunnel test is converted to the real bridge.The results show that the vortex amplitude of different pedestrian bridge design schemes meets the specification requirements at 20m/s wind speed.(3)Comparing the differences of comfort indicators in the design rules of footbridges in different countries,combined with the data of vortex-induced resonance wind tunnel tests,the comfort of different pedestrian bridge design schemes was evaluated.The results show that,except for the poor comfort of individual solutions,most of the footbridge design schemes are very comfortable.The research results of the thesis also provide a necessary reference for the wind-resistant design of the long-span footbridge.