Study On Wind-induced And Human Induced Vibration Response And TDM Scheme Of Pedestrian Bridge

With the development of urbanization and tourist attractions in China,the construction of pedestrian bridge represented by glass deck is in the ascendant,and it has the characteristics of "small stiffness,light weight and low damping",and the structure shape is more peculiar.In this paper,two typical cable-supported pedestrian bridges are taken as the object of study.Through wind tunnel test and finite element analysis,the wind-induced and human induced vibration responses of them are studied,and the parameter design and optimization scheme of commonly used tuned mass damper(TMD)are studied.The main work and achievements are as follows:(1)Through the wind tunnel test of aeroelastic model or segmental model,it is found that the flutter stability of the single cantilever cable-stayed footbridge with slotted variable cross-section is excellent,but the vortex performance is particularly poor.The critical wind speed of flutter is more than 104.4m/s under 9 kinds of working conditions,and vortex induced resonance of first-order vertical bending,first-order torsion and second-order vertical bending occurs under 5 kinds of working conditions.The scheme of ventilation railing can eliminate the vortex vibration of each stage.The problem of flutter and vortex(vertical bending and torsion)exists in the pedestrian suspension bridge with longitudinal and transverse steel frame and glass deck.When a 30 cm thick nozzle is installed,the critical flutter wind speed can be increased above the flutter test wind speed,but vortex induced resonance can not be eliminated.(2)Based on the German bridge design guidelines and finite element analysis,it can be seen that the acceleration response of human induced vibration at each point of the single cantilever cable-stayed bridge girder is positively correlated with the vibration mode displacement.With the change of time,the acceleration has the rule of "first increasing,then decreasing,then stabilizing".With the increase of population density,the number of equivalent simultaneous passengers increases nonlinearly,and the acceleration is proportional to it.The gathering of tourists at the end is beneficial to their vibration performance.The wind resistant cables arranged symmetrically on the pedestrian suspension bridge can reduce the transfinite mode of vertical and lateral acceleration and increase the critical number of lateral instability.With the increase of horizontal tension,the number of lateral and vertical transfinite modes is almost the same,and the critical number of lateral instability will increase linearly,but the response of the second-order vertical foot load will gradually become prominent.Asymmetric layout can still improve the vertical pedestrian comfort,but it will lead to the coupling of side bending and vertical bending vibration,reducing the lateral comfort of the pedestrian bridge.(3)According to the finite element analysis or wind tunnel test,for the secondorder vertical bending human induced vibration of single cantilever cable-stayed bridge,the damping ratio of the second-order vertical bending TMD is 77.03%,while the damping ratio of the third-order and second-order vertical bending TMD is only increased by 0.26%.The damping ratio of TMD will be reduced by about 30% near the mode stagnation point.After the arrangement of STMD,the first-order vertical bending,the first-order torsion and the second-order vertical bending vortex vibration damping efficiency reached 46%,47% and 77% respectively.The wind speed locking interval of vortex vibration remained unchanged,and the wind speed corresponding to the maximum amplitude decreased.(4)Combined with the single degree of freedom resonance theory,it can be found that STMD will consider one thing and lose the other when controlling the human induced vibration of pedestrian suspension bridge with dense sensitive frequency.According to the average modal mass and the out of limit modal frequency range(1.5～2.1hz),the mass ratio and damping ratio are taken as 0.01 and 0.061 respectively.A set of MTMD system can be designed to reduce the peak acceleration of all modes below the comfort limit.When the frequency range of MTMD is shifted to the right by 0.1Hz,there is no obvious change in the damping effect.If the mass ratio is halved,the frequency spacing is halved,and the number of TMD is doubled,the damping efficiency will be higher.