Dynamic Characteristics And Wind Environment Analysis Of Pedestrian Suspension Bridge In Mountain Area

In this paper,a pedestrian suspension bridge in a mountainous area is taken as the engineering background.The spatial structure model is established by using the finite element software Midas/Civil 2015.The difference of mass matrix model in the analysis of the natural vibration characteristics of the structure is compared.The dynamic characteristics are calculated by using the consistent mass matrix model.The influence of the stiffness change of the main cable,suspension bar and bridge tower on the natural vibration characteristics of the pedestrian suspension bridge is analyzed.The wind field at the bridge site in the mountain area was measured.The wind speed,wind direction,wind scale and the measured fluctuating wind characteristics are analyzed.Through the comparison and analysis of different working conditions,the influence of the cross-sling system and central buckle on the wind resistance stability of the structure is studied.The structure optimization scheme is put forward.The vertical cross cables,horizontal cross cables and single-gang rigid central buckle are combined into the optimization scheme.The dynamic characteristics of the optimized scheme after adopting wind resistance measures are analyzed.The specific research results obtained include :(1)Choosing different mass matrix modes will cause difference in the analysis of the natural vibration characteristics of suspension bridge.In the analysis of dynamic characteristics of flexible pedestrian suspension bridge,it is suggested that the extraction of low order modal can be done by lumped mass matrix model and consistent mass matrix model.The consistent mass matrix model is needed for the extraction of higher-order modes.(2)The first order natural vibration frequency of the suspension bridge is lower and its structural flexibility is larger.The symmetrical bend frequency ratio is lower,the torsional stiffness is weaker,and the stability of wind resistance is poorer.The change of stiffness of the main cable has little effect on the fundamental frequency of lateral and vertical bending of the bridge,but has a relatively greater influence on the fundamental frequency of the bridge’s torsion.The change of stiffness of the sling and cable tower have little effect on the fundamental frequency of lateral bending,vertical bending and torsional of the bridge.(3)The change range of wind speed and wind direction at the bridge site of mountain area is large,the gust is frequent and strong,and the wind environment is obvious in the mountain area.The spring and autumn season have more windy days and the spring wind speed is slightly higher than the autumn wind speed.The night and afternoon are the windy periods.The maximum daily wind speed of the measured period is 13.4 m/s.It will have a certain influence on the bridge,and the corresponding measures of wind resistance should be taken.The measured maximum dispersion range of turbulence intensity in the downwind and crosswind directions in the spring strong wind period is in accordance with ±33% specified in the Code.Most of the measured peaks of the fluctuating wind power spectrum appear in the low frequency stage,and the high frequency band gradually attenuates,the degree of attenuation varies greatly.(4)The setting of the cross sling system and the central buckle are beneficial to the wind resistance of the structure.The settings are different,the effects are not the same.In the five cross sling schemes,the vertical cross cable and the 20 pairs of horizontal cross cables are better for improving the wind resistance of the structure.In the six central buckle schemes,the single joint rigid central buckle is better to improve the wind resistance of the structure.After taking structural measures,the dynamic characteristics and wind resistance stability of the optimized scheme are better than the original scheme.